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Quantum Mechanics
#67
Improv Eyes.

Quote:This is one of the implications of the well known but highly non-intuitive principle that looking at something changes it in the quantum realm.

Researchers achieve direct counterfactual quantum communication
May 5, 2017 by Christopher Packham report

[Image: 5763a9466fe23.jpg]
Credit: CC0 Public Domain
(Phys.org)—In the non-intuitive quantum domain, the phenomenon of counterfactuality is defined as the transfer of a quantum state from one site to another without any quantum or classical particle transmitted between them. Counterfactuality requires a quantum channel between sites, which means that there exists a tiny probability that a quantum particle will cross the channel—in that event, the run of the system is discarded and a new one begins. It works because of the wave-particle duality that is fundamental to particle physics: Particles can be described by wave function alone.


Well understood as a workable scheme by physicists, theoretical aspects of counterfactual communication have appeared in journals, but until recently, there have been no practical demonstrations of the phenomenon. Now, a collaborative of Chinese scientists has designed and experimentally tested a counterfactual communication system that successfully transferred a monochrome bitmap from one location to another using a nested version of the quantum Zeno effect. They have reported their results in the Proceedings of the National Academy of Sciences.
The quantum Zeno effect occurs when an unstable quantum system is subjected to a series of weak measurements. Unstable particles can never decay while they are being measured, and the system is effectively frozen with a very high probability. This is one of the implications of the well known but highly non-intuitive principle that looking at something changes it in the quantum realm.
Using this effect, the authors of the new study achieved direct communication between sites without carrier particle transmission. In the setup they designed, two single-photon detectors were placed in the output ports of the last of an array of beam splitters. According to the quantum Zeno effect, it's possible to predict which single-photon detector will "click" when photons are allowed to pass. The system's nested interferometers served to measure the state of the system, thereby preventing it from changing.
Alice transfers a single photon to the nested interferometer; it is detected by three single photon detectors, D0, D1 and Df. If D0 or D1 click, Alice concludes a logic result of one or zero. If Df clicks, the result is considered inconclusive, and is discarded in post-processing. After the communication of all bits, the researchers were able to reassemble the image—a monochrome bitmap of a Chinese knot. Black pixels were defined as logic 0, while white pixels were defined as logic 1.
The idea came from holography technology. The authors write, "In the 1940s, a new imaging technique—holography—was developed to record not only light intensity but also the phase of light. One may then pose the question: Can the phase of light itself be used for imaging? The answer is yes." In the experiment, the phase of light itself became the carrier of information, and the intensity of the light was irrelevant to the experiment.
The authors note that besides applications in quantum communication, the technique could be used for such activities as imaging ancient artifacts that would be damaged by directly shining light.
[Image: 1x1.gif] Explore further: A quantum effect allows infrared measurements to be performed by detecting visible light
More information: Direct counterfactual communication via quantum Zeno effect. PNAS 2017 ; published ahead of print April 25, 2017, DOI: 10.1073/pnas.1614560114
Abstract 
Intuition from our everyday lives gives rise to the belief that information exchanged between remote parties is carried by physical particles. Surprisingly, in a recent theoretical study [Salih H, Li ZH, Al-Amri M, Zubairy MS (2013) Phys Rev Lett 110:170502], quantum mechanics was found to allow for communication, even without the actual transmission of physical particles. From the viewpoint of communication, this mystery stems from a (nonintuitive) fundamental concept in quantum mechanics—wave-particle duality. All particles can be described fully by wave functions. To determine whether light appears in a channel, one refers to the amplitude of its wave function. However, in counterfactual communication, information is carried by the phase part of the wave function. Using a single-photon source, we experimentally demonstrate the counterfactual communication and successfully transfer a monochrome bitmap from one location to another by using a nested version of the quantum Zeno effect. 

Journal reference: Proceedings of the National Academy of Sciences


Read more at: https://phys.org/news/2017-05-counterfactual-quantum.html#jCp[url=https://phys.org/news/2017-05-counterfactual-quantum.html#jCp][/url]
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#68
Darwinism in Question with Discovery: Octopuses Edit Their Own Genes
[Image: picture-1128-1443128035.jpg?itok=h4dPh0P3]
By Eric Metaxas | May 8, 2017 | 2:15 PM EDT




[Image: octopus_wikimedia_commons_photo.jpg?itok=U_XTZzjF]
Octopus (Wikimedia Commons Photo)
Imagine being able to make yourself more intelligent than your genes allow. If you were a slimy, spineless bottom-dweller, that might be a welcome bonus.

What’s the most intelligent animal on the planet? There are a lot of ways to answer that, and depending on your standard, apes, crows, dolphins, and parrots could all be contenders. But none of these vertebrates (animals with backbones) can lay claim to the incredible feats of one highly-intelligent group of invertebrates. A group that—according to new research—ignores the rules laid down by Darwin and takes evolution into its own tentacles.

I’m talking about cephalopods—the octopi, squid, and cuttlefish, which are widely regarded as scoring at the top of their class. These Mensa-worthy mollusks have been known to open jars, climb in and out of their tanks, communicate via a kind of Morse-code, and can camouflage themselves to match their surroundings with startling accuracy, using colorful skin cells.

And as I told you some time ago on BreakPoint, these eight-armed wonders of the deep defy evolution by exhibiting traits usually found in higher vertebrates like us. It’s a mind-boggling coincidence that Darwinists have long dismissed with euphemisms like, “convergent evolution.”

But octopi, squid, and cuttlefish seem to have altogether missed the memo about Darwinism, because new science is revealing another way in which they defy evolution.

In a paper published in the journal, “Cell,” Tel Aviv University researchers Joshua Rosenthal and Eli Eisenberg report that unlike almost all other animals, cephalopods routinely bypass the instructions in their DNA and edit their own genes.
In biology class, you probably learned that ribonucleic acid, or RNA, transcribes and carries the information coded in deoxyribonucleic acid, or DNA, to protein-factories in the cells. These proteins, built based on instructions from the DNA, are what make up our bodies. But what if we could edit the messages in our RNA to change the kind of protein produced?


 As it happens, that’s what cephalopods do—on a scale unknown anywhere else in the animal kingdom, and specifically in one area of their bodies: their nervous systems and brains.

The Tel Aviv researchers found “tens of thousands” of such RNA recoding sites in cephalopods, allowing a creature like the octopus to essentially reprogram itself, adding “new riffs to its basic genetic blueprint.” In other words, these invertebrates don’t care that they didn’t inherit the smart genes. They make themselves smart, anyway.

Of course, an animal can’t be the author of its own intelligence, and this is not a process anyone believes cephalopods perform consciously. Rather, it is a marvelous piece of “adaptive programming” built-in to their biology.

Darwinists have tried to spin this feat as “a special kind of evolution.” But the folks at Evolution News cut through this nonsense and identify RNA editing for what it is: “non-evolution.”

“Neo-Darwinism did not make cephalopods what they are,” they write. “These highly intelligent and well-adapted animals edited their own genomes, so what possible need do they have for … blind, random, unguided” evolution?

This is also an emerging field of research, which means it’s possible, in theory, that other organisms make extensive use of RNA editing, and we’re just not aware of it, yet.

If, as one popular science website puts it, other creatures can “defy” the “central dogma” of genetics, the implications for Darwin’s “tree of life,” and his entire theory, are dire.

But if cephalopods and the complex information processing that makes them so unique are in fact the result of a Programmer—of a Designer—the waters of biology become far less inky.

Eric Metaxas is the host of the “Eric Metaxas Show,” a co-host of “BreakPoint” radio and a New York Times #1 best-selling author whose works have been translated into more than twenty languages.

Editor's Note: This piece was originally published by BreakPoint.
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#69
Magnetic switch turns strange quantum property on and off
Date:
May 25, 2017
Source:
National Institute of Standards and Technology (NIST)
Summary:
A research team has developed the first switch that turns on and off a quantum behavior called the Berry phase. The discovery promises to provide new insight into the fundamentals of quantum theory and may lead to new quantum electronic devices.
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[Image: 170525141541_1_540x360.jpg]
These images show the orbital paths of electrons trapped within a circular region within graphene. In the classical orbit (top image), an electron that travels in a complete circuit has the same physical state as when it started on the path. However, when an applied magnetic field reaches a critical value, (bottom image), an electron completing a circuit has a different physical state its original one. The change is called a Berry phase and the magnetic field acts as a switch to turn on the Berry phase. The result is that the electron is raised to a higher energy level.
[i]Credit: Christopher Gutiérrez, Daniel Walkup/NIST[/i]


When a ballerina pirouettes, twirling a full revolution, she looks just as she did when she started. But for electrons and other subatomic particles, which follow the rules of quantum theory, that's not necessarily so. When an electron moves around a closed path, ending up where it began, its physical state may or may not be the same as when it left.
Now, there is a way to control the outcome, thanks to an international research group led by scientists at the National Institute of Standards and Technology (NIST). The team has developed the first switch that turns on and off this mysterious quantum behavior. The discovery promises to provide new insight into the fundamentals of quantum theory and may lead to new quantum electronic devices.
To study this quantum property, NIST physicist and fellow Joseph A. Stroscio and his colleagues studied electrons corralled in special orbits within a nanometer-sized region of graphene -- an ultrastrong, single layer of tightly packed carbon atoms. The corralled electrons orbit the center of the graphene sample just as electrons orbit the center of an atom. The orbiting electrons ordinarily retain the same exact physical properties after traveling a complete circuit in the graphene. But when an applied magnetic field reaches a critical value, it acts as a switch, altering the shape of the orbits and causing the electrons to possess different physical properties after completing a full circuit.
The researchers report their findings in the May 26, 2017, issue of Science.
The newly developed quantum switch relies on a geometric property called the Berry phase, named after English physicist Sir Michael Berry who developed the theory of this quantum phenomenon in 1983. The Berry phase is associated with the wave function of a particle, which in quantum theory describes a particle's physical state. The wave function -- think of an ocean wave -- has both an amplitude (the height of the wave) and a phase -- the location of a peak or trough relative to the start of the wave cycle.
When an electron makes a complete circuit around a closed loop so that it returns to its initial location, the phase of its wave function may shift instead of returning to its original value. This phase shift, the Berry phase, is a kind of memory of a quantum system's travel and does not depend on time, only on the geometry of the system -- the shape of the path. Moreover, the shift has observable consequences in a wide range of quantum systems.
Although the Berry phase is a purely quantum phenomenon, it has an analog in non-quantum systems. Consider the motion of a Foucault pendulum, which was used to demonstrate Earth's rotation in the 19th century. The suspended pendulum simply swings back and forth in the same vertical plane, but appears to slowly rotate during each swing -- a kind of phase shift -- due to the rotation of Earth beneath it.
Since the mid-1980s, experiments have shown that several types of quantum systems have a Berry phase associated with them. But until the current study, no one had constructed a switch that could turn the Berry phase on and off at will. The switch developed by the team, controlled by a tiny change in an applied magnetic field, gives electrons a sudden and large increase in energy.
Several members of the current research team -- based at the Massachusetts Institute of Technology and Harvard University -- developed the theory for the Berry phase switch.
To study the Berry phase and create the switch, NIST team member Fereshte Ghahari built a high-quality graphene device to study the energy levels and the Berry phase of electrons corralled within the graphene.
First, the team confined the electrons to occupy certain orbits and energy levels. To keep the electrons penned in, team member Daniel Walkup created a quantum version of an electric fence by using ionized impurities in the insulating layer beneath the graphene. This enabled a scanning tunneling microscope at NIST's nanotechnology user facility, the Center for Nanoscale Science and Technology, to probe the quantum energy levels and Berry phase of the confined electrons.
The team then applied a weak magnetic field directed into the graphene sheet. For electrons moving in the clockwise direction, the magnetic field created tighter, more compact orbits. But for electrons moving in counterclockwise orbits, the magnetic field had the opposite effect, pulling the electrons into wider orbits. At a critical magnetic field strength, the field acted as a Berry phase switch. It twisted the counterclockwise orbits of the electrons, causing the charged particles to execute clockwise pirouettes near the boundary of the electric fence.
Ordinarily, these pirouettes would have little consequence. However, says team member Christopher Gutiérrez, "the electrons in graphene possess a special Berry phase, which switches on when these magneticallyinduced pirouettes are triggered."
When the Berry phase is switched on, orbiting electrons abruptly jump to a higher energy level. The quantum switch provides a rich scientific tool box that will help scientists exploit ideas for new quantum devices, which have no analog in conventional semiconductor systems, says Stroscio.


Journal Reference:
  1. F. Ghahari, D. Walkup, C. Gutiérrez, J.F. Rodriguez-Nieva, Y. Zhao, J. Wyrick, F.D. Natterer, W.G. Cullen, K. Watanabe, T. Taniguchi, L.S. Levitov, N.B. Zhitenev, J.A. Stroscio. An on/off Berry phase switch in circular graphene resonatorsScience, 2017 DOI: 10.1126/science.aal0212

National Institute of Standards and Technology (NIST). "Magnetic switch turns strange quantum property on and off." ScienceDaily. ScienceDaily, 25 May 2017. <www.sciencedaily.com/releases/2017/05/170525141541.htm>.



Unveiling the quantum necklace
Researchers simulate quantum necklace-like structures in superfluids
Date:
May 25, 2017
Source:
Okinawa Institute of Science and Technology (OIST) Graduate University
Summary:
The quantum world is both elegant and mysterious. It is a sphere of existence where the laws of physics experienced in everyday life are broken -- particles can exist in two places at once, they can react to each other over vast distances, and they themselves seem confused over whether they are particles or waves. For those not involved in the field, this world may seem trifling, but recently, researchers have theoretically described two quantum states that are extraordinary in both the physics that define them and their visual appeal: a complex quantum system that simulates classical physics and a spellbinding necklace-like state.

[Image: 170525100311_1_540x360.jpg]
The number of pearls in the quantum necklace depends on the strength of the spin-orbit coupling. A stronger coupling produces more pearls, and the number must always be odd.
[i]Credit: Okinawa Institute of Science and Technology Graduate University[/i]


The quantum world is both elegant and mysterious. It is a sphere of existence where the laws of physics experienced in everyday life are broken -- particles can exist in two places at once, they can react to each other over vast distances, and they themselves seem confused over whether they are particles or waves. For those not involved in the field, this world may seem trifling, but recently, researchers from the Okinawa Institute of Science and Technology Graduate University (OIST) have theoretically described two quantum states that are extraordinary in both the physics that define them and their visual appeal: a complex quantum system that simulates classical physics and a spellbinding necklace-like state. Their study is published in the journal Physical Review A.
The quest for these states begins with a doughnut, or rather, a doughnut-shaped container housing a rotating superfluid. This superfluid, which is a fluid that moves with no friction, is made of Bose-Einstein condensates (BECs) comprising particles with no charge that are cooled to near-zero degrees kelvin, a temperature so cold, that it does not exist in the universe outside of laboratories. At this temperature, particles begin to exhibit strange properties -- they clump together, and eventually become indistinguishable from one another. In effect, they become a single entity and thus move as one.
Since this whirling BEC superfluid is operating at a quantum scale, where tiny distances and low temperatures reign, the physical characteristics of its rotation are not those seen in the classical world. Consider a father who is swinging his daughter around in a circle by the arms. Classical physics mandates that the child's legs will move faster than her hands around the circle, since her legs must travel further to make a complete turn.
In the world of quantum physics the relationship is the opposite. "In a superfluid...things which are very far away [from the center] move really slowly, whereas things [that] are close to the center move very fast," explains OIST Professor Thomas Busch, one of the researchers involved in the study. This is what is happening in the superfluid doughnut.
In addition, the superfluid inside of the doughnut shows a uniform density profile, meaning that it is distributed around the doughnut evenly. This would be the same for most liquids that are rotating via classical or quantum rules. But what happens if another type of BEC is added, one that is made from a different atomic species and that cannot mix with the original BEC? Like oil and water, the two components will separate in a way that minimizes the area in which they are touching and form two semicircles on opposite sides of the doughnut container.
"The shortest boundary [between the components] is in the radial direction," Dr. Angela White, first author on the study, explains. The two components separate into different halves of the doughnut along this boundary, which is created by passing through the doughnut's radius. In this configuration, they will use less energy to remain separated than they would via any other.
In the immiscible, or unmixable, configuration, the quantum world surprises. Since the boundary between the two superfluids must remain aligned along the radial direction, the superfluid present at this boundary must rotate like a classical object. This happens in order to maintain that low-energy state. If at the boundary the superfluids continued to rotate faster on the inside, then the two semicircles would start to twist, elongating the line that separates them, and thus requiring more energy to stay separated. The result is a sort of classical physics mimicry, where the system appears to jump into the classical realm, facilitated by complex quantum mechanical behavior.
At this stage, the superfluid doughnut has reached its first extraordinary state which is one that mimics classical rotation. But there is one more step needed to transform this already mind-boggling system into the necklace end-goal: spin-orbit coupling.
"In a very abstract way, [spin is] just a thing that has two possible states," Busch explains. "It can be this way or it can be that way." For this experiment, which involves particles that have no charge, or no spin, the researchers "faked" a spin by assigning a "this or that" property to their particles.
When coupling the particles based on this property, the two semicircles inside of the doughnut break into multiple alternating parts, thus forming the necklace configuration. By digging further into its composition, the researchers found that the number of "pearls" in the necklace depends on the strength of the spin-orbit coupling and, more surprisingly, that there must always be an odd number of these pearls.
Researchers have predicted quantum necklaces before, but they were known to be unstable -- expanding or dissipating themselves to oblivion only a short time after being created. In this theoretical model, the OIST researchers believe they have found a way to create a stable necklace, one that would allow for more time to study it and appreciate its refined majesty.


Journal Reference:
  1. Angela C. White, Yongping Zhang, Thomas Busch. Odd-petal-number states and persistent flows in spin-orbit-coupled Bose-Einstein condensatesPhysical Review A, 2017; 95 (4) DOI: 10.1103/PhysRevA.95.041604


Okinawa Institute of Science and Technology (OIST) Graduate University. "Unveiling the quantum necklace: Researchers simulate quantum necklace-like structures in superfluids." ScienceDaily. ScienceDaily, 25 May 2017. <www.sciencedaily.com/releases/2017/05/170525100311.htm>.
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#70
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Physicists settle debate over how exotic quantum particles form

June 23, 2017 by Carla Reiter



[Image: physicistsse.jpg]
Here “3” symbolizes an Efimov molecule comprised of three atoms. While all “3”s look about the same, research from the Chin group observed a tiny “3” that is clearly different. Credit: Cheng Chin
New research by physicists at the University of Chicago settles a longstanding disagreement over the formation of exotic quantum particles known as Efimov molecules.





The findings, published last month in Nature Physics, address differences between how theorists say Efimov molecules should form and the way researchers say they did form in experiments. The study found that the simple picture scientists formulated based on almost 10 years of experimentation had it wrong—a result that has implications for understanding how the first complex molecules formed in the early universe and how complex materials came into being.
Efimov molecules are quantum objects formed by three particles that bind together when two particles are unable to do so. The same three particles can make molecules in an infinite range of sizes, depending on the strength of the interactions between them.
Experiments had shown the size of an Efimov molecule was roughly proportional to the size of the atoms that comprise it—a property physicists call universality.
"This hypothesis has been checked and rechecked multiple times in the past 10 years, and almost all the experiments suggested that this is indeed the case," said Cheng Chin, a professor of physics at UChicago, who leads the lab where the new findings were made. "But some theorists say the real world is more complicated than this simple formula. There should be some other factors that will break this universality."
The new findings come down somewhere between the previous experimental findings and predictions of theorists. They contradict both and do away with the idea of universality.
"I have to say that I am surprised," Chin said. "This was an experiment where I did not anticipate the result before we got the data."
The data came from extremely sensitive experiments done with cesium and lithium atoms using techniques devised by Jacob Johansen, previously a graduate student in Chin's lab who is now a postdoctoral fellow at Northwestern University. Krutik Patel, a graduate student at UChicago, and Brian DeSalvo, a postdoctoral researcher at UChicago, also contributed to the work.
"We wanted to be able to say once and for all that if we didn't see any dependence on these other properties, then there's really something seriously wrong with the theory," Johansen said. "If we did see dependence, then we're seeing the breakdown of this universality. It always feels good, as a scientist, to resolve these sorts of questions."


Developing new techniques
Efimov molecules are held together by quantum forces rather than by the chemical bonds that bind together familiar molecules such as H2O. The atoms are so weakly connected that the molecules can't exist under normal conditions. Heat in a room providing enough energy to shatter their bonds.
The Efimov molecule experiments were done at extremely low temperatures—50 billionths of a degree above absolute zero—and under the influence of a strong magnetic field, which is used to control the interaction of the atoms. When the field strength is in a particular, narrow range, the interaction between atoms intensifies and molecules form. By analyzing the precise conditions in which formation occurs, scientists can infer the size of the molecules.
But controlling the magnetic field precisely enough to make the measurements Johansen sought is extremely difficult. Even heat generated by the electric current used to create the field was enough to change that field, making it hard to reproduce in experiments. The field could fluctuate at a level of only one part in a million—a thousand times weaker than the Earth's magnetic field—and Johansen had to stabilize it and monitor how it changed over time.
The key was a technique he developed to probe the field using microwave electronics and the atoms themselves.
"I consider what Jacob did a tour de force," Chin said. "He can control the field with such high accuracy and perform very precise measurements on the size of these Efimov molecules and for the first time the data really confirm that there is a significant deviation of the universality."
The new findings have important implications for understanding the development of complexity in materials. Normal materials have diverse properties, which could not have arisen if their behavior at the quantum level was identical. The three-body Efimov system puts scientists right at the point at which universal behavior disappears.
"Any quantum system made with three or more particles is a very, very difficult problem," Chin said. "Only recently do we really have the capability to test the theory and understand the nature of such molecules. We are making progress toward understanding these small quantum clusters. This will be a building block for understanding more complex material."
[Image: 1x1.gif] Explore further: Exotic, gigantic molecules fit inside each other like Russian nesting dolls
More information: Jacob Johansen et al. Testing universality of Efimov physics across broad and narrow Feshbach resonances, Nature Physics (2017). DOI: 10.1038/nphys4130 
Journal reference: Nature Physics [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: University of Chicago



Read more at: https://phys.org/news/2017-06-physicists...s.html#jCp

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#71
Physicists read Maxwell's Demon's mind
July 5, 2017


Pioneering research offers a fascinating view into the inner workings of the mind of 'Maxwell's Demon', a famous thought experiment in physics.


An international research team, including Dr Janet Anders from the University of Exeter, have used superconducting circuits to bring the 'demon' to life.
The demon, first proposed by James Clerk Maxwell in 1867, is a hypothetical being that can gain more useful energy from a thermodynamic system than one of the most fundamental laws of physics—the second law of thermodynamics—should allow.
Crucially, the team not only directly observed the gained energy for the first time, they also tracked how information gets stored in the demon's memory.
The research is published in the leading scientific journal Proceedings of the National Academy of Sciences (PNAS).
The original thought experiment was first proposed by mathematical physicist James Clerk Maxwell—one of the most influential scientists in history—150 years ago.
He hypothesised that gas particles in two adjacent boxes could be filtered by a 'demon' operating a tiny door, that allowed only fast energy particles to pass in one direction and low energy particles the opposite way.
As a result, one box gains a higher average energy than the other, which creates a pressure difference. This non-equilibrium situation can be used to gain energy, not unlike the energy obtained when water stored behind a dam is released.
So although the gas was initially in equilibrium, the demon can create a non-equilibrium situation and extract energy, bypassing the second law of thermodynamics.
Dr Anders, a leading theoretical physicist from the University of Exeter's physics department adds: "In the 1980s it was discovered that this is not the full story. The information about the particles' properties remains stored in the memory of the demon. This information leads to an energetic cost which then reduces the demon's energy gain to null, resolving the paradox."
In this research, the team created a quantum Maxwell demon, manifested as a microwave cavity, that draws energy from a superconducting qubit. The team was able to fully map out the memory of the demon after its intervention, unveiling the stored information about the qubit state.
Dr Anders adds: "The fact that the system behaves quantum mechanically means that the particle can have a high and low energy at the same time, not only either of these choices as considered by Maxwell."
This ground-breaking experiment gives a fascinating peek into the interplay between quantum information and thermodynamics, and is an important step in the current development of a theory for nanoscale thermodynamic processes.
'Observing a Quantum Maxwell demon at Work' is published in PNAS.
[Image: 1x1.gif] Explore further: Physicists create first photonic Maxwell's demon
More information: Nathanaël Cottet et al. Observing a quantum Maxwell demon at work, Proceedings of the National Academy of Sciences (2017). DOI: 10.1073/pnas.1704827114 
Journal reference: Proceedings of the National Academy of Sciences[Image: img-dot.gif] [Image: img-dot.gif]
Provided by: University of Exeter



Read more at: https://phys.org/news/2017-07-physicists...d.html#jCp[/url]





Maxwell's demon extracts work from quantum measurement

July 10, 2017 by Lisa Zyga 
feature



[Image: maxwellsdemon.jpg]
The new Maxwell’s demon extracts work from a system by making a quantum measurement. Credit: Elouard et al. ©2017 American Physical Society
(Phys.org)—Physicists have proposed a new type of Maxwell's demon—the hypothetical agent that extracts work from a system by decreasing the system's entropy—in which the demon can extract work just by making a measurement, by taking advantage of quantum fluctuations and quantum superposition.





The team of Alexia Auffèves at CNRS and Université Grenoble Alpes have published a paper on the new Maxwell's demon in a recent issue of Physical Review Letters.
"In the classical world, thermodynamics teaches us how to extract energy from thermal fluctuations induced on a large system (such as a gas or water) by coupling it to a hot source," Auffèves told Phys.org. "In the quantum world, the systems are small, and they can fluctuate—even if they are not hot, but simply because they are measured. In our paper, we show that it is possible to extract energy from these genuinely quantum fluctuations, induced by quantum measurement."
In the years since James Clerk Maxwell proposed the first demon around 1870, many other versions have been theoretically and experimentally investigated. Most recently, physicists have begun investigating Maxwell's demons that operate in the quantum regime, which could one day have implications for quantum information technologies.
Most quantum versions of the demon have a couple things in common: They are thermally driven by a heat bath, and the demon makes measurements to extract information only. The measurements do not actually extract any work, but rather the information gained by the measurements allows the demon to act on the system so that energy is always extracted from the cycle.
The new Maxwell's demon differs from previous versions in that there is no heat bath—the demon is not thermally driven, but measurement-driven. Also, the measurements have multiple purposes: They not only extract information about the state of the system, but they are also the "fuel" for extracting work from the system. This is because, when the demon performs a measurement on a qubit in the proposed system, the measurement projects the qubit from one state into a superposition of states, which provides energy to the qubit simply due to the measurement process. In their paper, the physicists proposed an experiment in which projective quantum non-demolition measurements can be performed with light pulses repeated every 70 nanoseconds or so.
Since recent experiments have already demonstrated the possibility of performing measurements at such high frequencies, the physicists expect that the new Maxwell's demon could be readily implemented using existing technology. In the future, they also plan to investigate potential applications for quantum computing.
"This engine is a perfect proof of concept evidencing that quantum measurement has some energetic footprint," Auffèves said. "Now I would like to reverse the game and use this effect to estimate the energetic cost of quantum tasks, if they are performed in the presence of some measuring entity. This is the case in a quantum computer, which is continuously 'measured' by its surroundings. This effect is called decoherence and is the biggest enemy of quantum computation. Our work provides tools to estimate the energy needed to counteract it."
[Image: 1x1.gif] Explore further: Physicists read Maxwell's Demon's mind
More information: Cyril Elouard et al. "Extracting Work from Quantum Measurement in Maxwell's Demon Engines." Physical Review Letters. DOI: 10.1103/PhysRevLett.118.260603, Also at arXiv:1702.01917 [quant-ph] 
Journal reference: Physical Review Letters


Read more at: https://phys.org/news/2017-07-maxwell-de...m.html#jCp



Physicists transmit data via Earth-to-space quantum entanglement

July 11, 2017 by Bob Yirka report



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Overview of the set-up for ground-to-satellite quantum teleportation of a single photon with a distance up to 1400 km. Credit: arXiv:1707.00934 [quant-ph]
(Phys.org)—Two teams of researchers in China have advanced the distance that entangled particles can be used to send information, including encryption keys. In their papers, both uploaded to the arXiv preprint sever, the two groups outline their work and suggest their achievement represents an essential step toward the development of a global-scale quantum internet.





Quantum entanglement is the shared state of two separate particles—what happens to one happens to the other. Scientists have not yet figured out how this occurs, but they have learned how to create entangled particles on demand, typically by firing a laser through a crystal. As physicists learn more about entangled particles, they've designed more experiments to take advantage of their unique properties. One such area of research involves using them to build quantum networks. Such networks would be much faster than anything we have now, and they would also be much more secure because of the nature of entangled particles—disruptions to encryption keys, for example, could be instantly noted, allowing for prevention of hacking. In this new effort, the researchers have extended the entanglement distance of two particles—one on the surface of the Earth and the other in space, courtesy of a satellite. They have also shown that it is possible to send entangled encryption keys from a satellite to an Earth-based receiving station.
In the first experiment, the research team transferred the properties of an entangled particle housed in a facility in Tibet to its partner, which was beamed to a satellite passing overhead, far surpassing the distance record by other researchers. In this case, the information transfer occurred with photons that were approximately 500 to 1,400 kilometers apart, depending on the location of the satellite.
In the second experiment, equipment aboard a satellite created a random string of numbers to represent an encryption key. The key was then beamed to an Earth station as part of an entangled photon stream that used polarization as a means of transmission security.
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Illustration of the experimental set-up from "Satellite-to-ground quantum key distribution" arXiv:1707.00542 [quant-ph]
[Image: 1x1.gif] Explore further: Big scientific breakthrough at sub-atomic level holds promise for secure comms
More information: * Ground-to-satellite quantum teleportation, arXiv:1707.00934 [quant-ph] arxiv.org/abs/1707.00934
Abstract 
An arbitrary unknown quantum state cannot be precisely measured or perfectly replicated. However, quantum teleportation allows faithful transfer of unknown quantum states from one object to another over long distance, without physical travelling of the object itself. Long-distance teleportation has been recognized as a fundamental element in protocols such as large-scale quantum networks and distributed quantum computation. However, the previous teleportation experiments between distant locations were limited to a distance on the order of 100 kilometers, due to photon loss in optical fibres or terrestrial free-space channels. An outstanding open challenge for a global-scale "quantum internet" is to significantly extend the range for teleportation. A promising solution to this problem is exploiting satellite platform and space-based link, which can conveniently connect two remote points on the Earth with greatly reduced channel loss because most of the photons' propagation path is in empty space. Here, we report the first quantum teleportation of independent single-photon qubits from a ground observatory to a low Earth orbit satellite - through an up-link channel - with a distance up to 1400 km. To optimize the link efficiency and overcome the atmospheric turbulence in the up-link, a series of techniques are developed, including a compact ultra-bright source of multi-photon entanglement, narrow beam divergence, high-bandwidth and high-accuracy acquiring, pointing, and tracking (APT). We demonstrate successful quantum teleportation for six input states in mutually unbiased bases with an average fidelity of 0.80+/-0.01, well above the classical limit. This work establishes the first ground-to-satellite up-link for faithful and ultra-long-distance quantum teleportation, an essential step toward global-scale quantum internet.

* Satellite-to-ground quantum key distribution, arXiv:1707.00542 [quant-ph] arxiv.org/abs/1707.00542
Abstract 
Quantum key distribution (QKD) uses individual light quanta in quantum superposition states to guarantee unconditional communication security between distant parties. In practice, the achievable distance for QKD has been limited to a few hundred kilometers, due to the channel loss of fibers or terrestrial free space that exponentially reduced the photon rate. Satellite-based QKD promises to establish a global-scale quantum network by exploiting the negligible photon loss and decoherence in the empty out space. Here, we develop and launch a low-Earth-orbit satellite to implement decoy-state QKD with over kHz key rate from the satellite to ground over a distance up to 1200 km, which is up to 20 orders of magnitudes more efficient than that expected using an optical fiber (with 0.2 dB/km loss) of the same length. The establishment of a reliable and efficient space-to-ground link for faithful quantum state transmission constitutes a key milestone for global-scale quantum networks. 

Journal reference: arXiv


Read more at: https://phys.org/news/2017-07-physicists-transmit-earth-to-space-quantum-entanglement.html#jCp[url=https://phys.org/news/2017-07-physicists-transmit-earth-to-space-quantum-entanglement.html#jCp]
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#72
Quantum LilD  heat treated.

Controlling heat and particle currents in nanodevices by quantum observation
July 14, 2017

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Artistic illustration of the role of a quantum observer in a nanodevice: When observing only the right part of the figure (covering the left part with the hand the water appears to flow down the channel, instead, by looking at the whole painting the water actually flows uphill. This apparent paradox mimics the coherent superposition of two quantum states (water flowing up and down). By observing at specific parts of our system we are able to tune between these two states and hence change the ‘physical response of the nanodevice’ in a controlled way. Credit: K. Aranburu
Researchers from the Theory Department of the MPSD have realized the control of thermal and electrical currents in nanoscale devices by means of quantum local observations.



Read more at: https://phys.org/news/2017-07-particle-c...m.html#jCp



Heat-loving quantum oscillations

July 14, 2017



[Image: heatlovingqu.jpg]
Credit: University of Manchester
The rapidly developing science and technology of graphene and atomically-thin materials has taken another step forward with new research from The University of Manchester.





Read more at: https://phys.org/news/2017-07-heat-loving-quantum-oscillations.html#jCp
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#73
New breakthrough discovery—every quantum particle travels backwards
July 18, 2017 by Saskia Angenent

[Image: 57dfe35e10c2e.jpg]
Credit: CC0 Public Domain
Mathematicians at the Universities of York, Munich and Cardiff have identified a unique property of quantum mechanical particles – they can move in the opposite way to the direction in which they are being pushed.


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In everyday life, objects travel in the same direction as their momentum – a car in forward motion is going forwards, and certainly not backwards.
However, this is no longer true on microscopic scales - quantum particles can partially go into reverse and travel in the direction opposite to their momentum. This unique property is known as 'backflow'.
New discovery
This is the first time this has been found in a particle where external forces are acting on it. Previously, scientists were only aware of this movement in "free" quantum particles, where no force is acting on them.
Using a combination of analytical and numerical methods, researchers also obtained precise estimates about the strength of this phenomenon. Such results demonstrate that backflow is always there but is a rather small effect, which may explain why it has not been measured yet.
This discovery paves the way for further research into quantum mechanics, and could be applied to future experiments in quantum technology fields such as computer encryption.
Unique to quantum particles
Dr Henning Bostelmann, Researcher in York's Department of Mathematics, said: "This new theoretical analysis into quantum mechanical particles shows that this 'backflow' effect is ubiquitous in quantum physics.
"We have shown that backflow can always occur, even if a force is acting on the quantum particle while it travels. The backflow effect is the result of wave-particle duality and the probabilistic nature of quantum mechanics, and it is already well understood in an idealised case of force-free motion."
Dr Gandalf Lechner, Researcher in Cardiff's University's School of Mathematics, said: "Forces can of course make a particle go backwards - that is, they can reflect it, and this naturally leads to increased backflow. But we could show that even in a completely reflection-free medium, backflow occurs. In the presence of reflection, on the other hand, we found that backflow remains a small effect, and estimated its magnitude."
External forces
Dr Daniela Cadamuro, Researcher at the Technical University of Munich, said: "The backflow effect in quantum mechanics has been known for quite a while, but it has always been discussed in regards to 'free' quantum particles, i.e., no external forces are acting on the particle.
"As 'free' quantum particles are an idealised, perhaps unrealistic situation, we have shown that backflow still occurs when external forces are present. This means that external forces don't destroy the backflow effect, which is an exciting new discovery."
"These new findings allow us to find out the optimal configuration of a quantum particle that exhibits the maximal amount of backflow, which is important for future experimental verification."

[Image: 1x1.gif] Explore further: Breaking Newton's Law: Intriguing oscillatory back-and-forth motion of a quantum particle
More information: Henning Bostelmann et al. Quantum backflow and scattering, Physical Review A (2017). DOI: 10.1103/PhysRevA.96.012112 
Journal reference: Physical Review A [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: University of York



Read more at: https://phys.org/news/2017-07-breakthrough-discoveryevery-quantum-particle.html#jCp[url=https://phys.org/news/2017-07-breakthrough-discoveryevery-quantum-particle.html#jCp][/url]
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http://news.stanford.edu/2017/07/20/evid...iparticle/


An experiment proposed by Stanford theorists finds evidence for the Majorana fermion, a particle that’s its own antiparticle
In a discovery that concludes an 80-year quest, Stanford and University of California researchers found evidence of particles that are their own antiparticles. These 'Majorana fermions’  could one day help make quantum computers more robust. See video here. By Glennda Chui
In 1928, physicist Paul Dirac made the stunning prediction that every fundamental particle in the universe has an antiparticle – its identical twin but with opposite charge. When particle and antiparticle met they would be annihilated, releasing a poof of energy. Sure enough, a few years later the first antimatter particle – the electron’s opposite, the positron – was discovered, and antimatter quickly became part of popular culture.
[Image: majorana_zheng.jpg]

Shoucheng Zhang (Image credit: Courtesy SLAC National Accelerator Laboratory)
But in 1937, another brilliant physicist, Ettore Majorana, introduced a new twist: He predicted that in the class of particles known as fermions, which includes the proton, neutron, electron, neutrino and quark, there should be particles that are their own antiparticles.
Now a team including Stanford scientists says it has found the first firm evidence of such a Majorana fermion. It was discovered in a series of lab experiments on exotic materials at the University of California in collaboration with Stanford University. The team was led by UC-Irvine Associate Professor Jing Xia and UCLA Professor Kang Wang, and followed a plan proposed by Shoucheng Zhang, professor of physics at Stanford, and colleagues. The team reported the results July 20 in Science.
“Our team predicted exactly where to find the Majorana fermion and what to look for as its ‘smoking gun’ experimental signature,” said Zhang, a theoretical physicist and one of the senior authors of the research paper. “This discovery concludes one of the most intensive searches in fundamental physics, which spanned exactly 80 years.”
Although the search for the famous fermion seems more intellectual than practical, he added, it could have real-life implications for building robust quantum computers, although this is admittedly far in the future.
The particular type of Majorana fermion the research team observed is known as a “chiral” fermion because it moves along a one-dimensional path in just one direction. While the experiments that produced it were extremely difficult to conceive, set up and carry out, the signal they produced was clear and unambiguous, the researchers said.
“This research culminates a chase for many years to find chiral Majorana fermions. It will be a landmark in the field,” said Tom Devereaux, director of the Stanford Institute for Materials and Energy Sciences (SIMES) at SLAC National Accelerator Laboratory, where Zhang is a principal investigator.
“It does seem to be a really clean observation of something new,” said Frank Wilczek, a theoretical physicist and Nobel laureate at the Massachusetts Institute of Technology who was not involved in the study. “It’s not fundamentally surprising, because physicists have thought for a long time that Majorana fermions could arise out of the types of materials used in this experiment. But they put together several elements that had never been put together before, and engineering things so this new kind of quantum particle can be observed in a clean, robust way is a real milestone.”
Search for ‘quasiparticles’
Majorana’s prediction applied only to fermions that have no charge, like the neutron and neutrino.  Scientists have since found an antiparticle for the neutron, but they have good reasons to believe that the neutrino could be its own antiparticle, and there are four experiments underway to find out – including EXO-200, the latest incarnation of the Enriched Xenon Observatory, in New Mexico. But these experiments are extraordinarily difficult and are not expected to produce an answer for about a decade.
About 10 years ago, scientists realized that Majorana fermions might also be created in experiments that explore the physics of materials – and the race was on to make that happen.
What they’ve been looking for are “quasiparticles” – particle-like excitations that arise out of the collective behavior of electrons in superconducting materials, which conduct electricity with 100 percent efficiency. The process that gives rise to these quasiparticles is akin to the way energy turns into short-lived “virtual” particles and back into energy again in the vacuum of space, according to Einstein’s famous equation E = mc2. While quasiparticles are not like the particles found in nature, they would nonetheless be considered real Majorana fermions.
Over the past five years, scientists have had some success with this approach, reporting that they had seen promising Majorana fermion signatures in experiments involving superconducting nanowires.
But in those cases the quasiparticles were “bound” – pinned to one particular place, rather than propagating in space and time – and it was hard to tell if other effects were contributing to the signals researchers saw, Zhang said.
A ‘smoking gun’
In the latest experiments at UCLA and UC-Irvine, the team stacked thin films of two quantum materials – a superconductor and a magnetic topological insulator – and sent an electrical current through them, all inside a chilled vacuum chamber.
The top film was a superconductor. The bottom one was a topological insulator, which conducts current only along its surface or edges but not through its middle. Putting them together created a superconducting topological insulator, where electrons zip along two edges of the material’s surface without resistance, like cars on a superhighway.
It was Zhang’s idea to tweak the topological insulator by adding a small amount of magnetic material to it. This made the electrons flow one way along one edge of the surface and the opposite way along the opposite edge.
Then the researchers swept a magnet over the stack. This made the flow of electrons slow, stop and switch direction. These changes were not smooth, but took place in abrupt steps, like identical stairs in a staircase.
At certain points in this cycle, Majorana quasiparticles emerged, arising in pairs out of the superconducting layer and traveling along the edges of the topological insulator just as the electrons did. One member of each pair was deflected out of the path, allowing the researchers to easily measure the flow of the individual quasiparticles that kept forging ahead. Like the electrons, they slowed, stopped and changed direction – but in steps exactly half as high as the ones the electrons took.
These half-steps were the smoking gun evidence the researchers had been looking for.
The results of these experiments are not likely to have any effect on efforts to determine if the neutrino is its own antiparticle, said Stanford physics Professor Giorgio Gratta, who played a major role in designing and planning EXO-200.
“The quasiparticles they observed are essentially excitations in a material that behave like Majorana particles,” Gratta said. “But they are not elementary particles and they are made in a very artificial way in a very specially prepared material. It’s very unlikely that they occur out in the universe, although who are we to say? On the other hand, neutrinos are everywhere, and if they are found to be Majorana particles we would show that nature not only has made this kind of particles possible but, in fact, has literally filled the universe with them.”
He added, “Where it gets more interesting is that analogies in physics have proved very powerful. And even if they are very different beasts, different processes, maybe we can use one to understand the other. Maybe we will discover something that is interesting for us, too.”
Angel particle
Far in the future, Zhang said, Majorana fermions could be used to construct robust quantum computers that aren’t thrown off by environmental noise, which has been a big obstacle to their development. Since each Majorana is essentially half a subatomic particle, a single qubit of information could be stored in two widely separated Majorana fermions, decreasing the chance that something could perturb them both at once and make them lose the information they carry.
For now, he suggests a name for the chiral Majorana fermion his team discovered: the “angel particle,” in reference to the best-selling 2000 thriller “Angels and Demons” in which a secret brotherhood plots to blow up the Vatican with a time bomb whose explosive power comes from matter-antimatter annihilation. Unlike in the book, he noted, in the quantum world of the Majorana fermion there are only angels – no demons.
The materials used for this study were produced at UCLA by a team led by postdoctoral researcher Qing Lin He and graduate student Lei Pan. Scientists from the KACST Center for Excellence in Green Nanotechnology in Saudia Arabia, UC-Davis, Florida State University, Fudan University in Shanghai and Shanghai Tech University also contributed to the experiment. Major funding came from the SHINES Center, an Energy Frontier Research Center at UC-Riverside funded by the U.S. Department of Energy Office of Science. Zhang’s work was funded by the DOE Office of Science through SIMES.


Media Contacts
Amy Adams, Stanford News Service: (650) 796-3695, amyadams@stanford.edu
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#75
Quantum mechanics inside Earth's core
by Staff Writers
Wurzburg, Denmark (SPX) Jul 13, 2017


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illustration only

Without a magnetic field life on Earth would be rather uncomfortable: Cosmic particles would pass through our atmosphere in large quantities and damage the cells of all living beings. Technical systems would malfunction frequently and electronic components could be destroyed completely in some cases.
Despite its huge significance for life on our planet, it is still not fully known what creates the Earth's magnetic field. There are various theories regarding its origin, but a lot of experts consider them to be insufficient or flawed.
A discovery made by scientists from Wurzburg might provide a new explanatory angle. Their findings were published in the current issue of the journal Nature Communications. Accordingly, the key to the effect could be hidden in the special structure of the element nickel.
Contradiction between theory and reality
"The standard models for Earth's magnetic field use values for the electric and thermal conductivity of the metals inside our planet's core that cannot square with reality," Giorgio Sangiovanni says; he is a professor at the Institute for Theoretical Physics and Astrophysics at the University of Wurzburg. Together with PhD student Andreas Hausoel and postdoc Michael Karolak, he is in charge of the international collaboration that was published recently.
Among the participants are Alessandro Toschi and Karsten Held of TU Wien, who are long-term cooperation partners of Giorgio Sangiovanni, and scientists from Hamburg, Halle (Saale) and Yekaterinburg in Russia.
At Earth's centre at a depth of about 6,400 km, there is a temperature of 6,300 degrees Celsius and a pressure of about 3.5 million bars. The predominant elements, iron and nickel, form a solid metal ball under these conditions which makes up the inner core of the Earth.
This inner core is surrounded by the outer core, a fluid layer composed mostly of iron and nickel. Flowing of liquid metal in the outer core can intensify electric currents and create Earth's magnetic field - at least according to the common geodynamo theory. "But the theory is somewhat contradictory," Giorgio Sangiovanni says.
Band-structure induced correlation effects
"This is because at room temperature iron differs significantly from common metals such as copper or gold due to its strong effective electron-electron interaction. It is strongly correlated," he declares.
But the effects of electron correlation are attenuated considerably at the extreme temperatures prevailing in Earth's core so that conventional theories are applicable. These theories then predict a much too high thermal conductivity for iron which is at odds with the geodynamo theory.
With nickel things are different. "We found nickel to exhibit a distinct anomaly at very high temperatures," the physicist explains.
"Nickel is also a strongly correlated metal. Unlike iron, this is not due to the electron-electron interaction alone, but is mainly caused by the special band structure of nickel. We baptised the effect 'band-structure induced correlation'." The band structure of a solid is only determined by the geometric layout of the atoms in the lattice and by the atom type.
Iron and nickel in Earth's core
"At room temperature, iron atoms will arrange in a way that the corresponding atoms are located at the corners of an imaginary cube with one central atom at the centre of the cube, forming a so-called bcc lattice structure," Andreas Hausoel adds. But as temperature and pressure increase, this structure changes: The atoms move together more closely and form a hexagonal lattice, which physicists refer to as an hcp lattice. As a result, iron looses most of its correlated properties.
But not so with nickel: "In this metal, the atoms are as densely packed as possible in the cube structure already in the normal state. They keep this layout even when temperature and pressure become very large," Hausoel explains. The unusual physical behaviour of nickel under extreme conditions can only be explained by the interaction of this geometric stability and the electron correlations originating from this geometry. Despite the fact that scientists have neglected nickel so far, it seems to play a major role in Earth's magnetic field.
Decisive hint from geophysics
The goings-on inside Earth's core are not the actual focus of research at the Departments of Theoretical Solid-state Physics of the University of Wurzburg. Rather Sangiovanni, Hausoel and their colleagues concentrate on the properties of strongly correlated electrons at low temperatures.
They study quantum effects and so-called multi-particle effects which are interesting for the next generation of data processing and energy storage devices. Superconductors and quantum computers are the keywords in this context.
Data from experiments are not used in this kind of research. "We take the known properties of atoms as input, include the insights from quantum mechanics and try to calculate the behaviour of large clusters of atoms with this," Hausoel says. Because such calculations are highly complex, the scientists have to rely on external support such as the SUPERMUC supercomputer at the Leibniz Supercomputing Centre (LRZ) in Garching.
And what's the Earth's core got to do with this? "We wanted to see how stable the novel magnetic properties of nickel are and found them to survive even very high temperatures," Hausoel says. Discussions with geophysicists and further studies of iron-nickel alloys have shown that these discoveries could be relevant for what is happening inside Earth's core.
Research paper
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A single photon reveals quantum entanglement of 16 million atoms
October 13, 2017

[Image: asinglephoto.jpg]
Partial view of the source producing the single photons that were stored in the quantum memory to produce entanglement between many atoms inside the memory. Credit: UNIGE
Quantum theory predicts that a vast number of atoms can be entangled and intertwined by a very strong quantum relationship, even in a macroscopic structure. Until now, however, experimental evidence has been mostly lacking, although recent advances have shown the entanglement of 2,900 atoms. Scientists at the University of Geneva (UNIGE), Switzerland, recently reengineered their data processing, demonstrating that 16 million atoms were entangled in a one-centimetre crystal. They have published their results in Nature Communications.



Read more at: https://phys.org/news/2017-10-photon-reveals-quantum-entanglement-million.html#jCp
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https://cosmosmagazine.com/physics/unive...s-conclude

One of the great mysteries of modern physics is why antimatter did not destroy the universe at the beginning of time.
To explain it, physicists suppose there must be some difference between matter and antimatter – apart from electric charge. Whatever that difference is, it’s not in their magnetism, it seems.
Physicists at CERN in Switzerland have made the most precise measurement ever of the magnetic moment of an anti-proton – a number that measures how a particle reacts to magnetic force – and found it to be exactly the same as that of the proton but with opposite sign. The work is described in Nature.
“All of our observations find a complete symmetry between matter and antimatter, which is why the universe should not actually exist,” says Christian Smorra, a physicist at CERN’s Baryon–Antibaryon Symmetry Experiment (BASE) collaboration. “An asymmetry must exist here somewhere but we simply do not understand where the difference is.”
Antimatter is notoriously unstable – any contact with regular matter and it annihilates in a burst of pure energy that is the most efficient reaction known to physics. That’s why it was chosen as the fuel to power the starship Enterprise in Star Trek.
The standard model predicts the Big Bang should have produced equal amounts of matter and antimatter – but that’s a combustive mixture that would have annihilated itself, leaving nothing behind to make galaxies or planets or people.
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#78
Quan­tum physics turned into tan­gi­ble re­al­ity
January 16, 2018 by Fe­lix Würsten, ETH Zurich


[Image: quantumphysi.jpg]
When the silicon wafer is stimulated at a single point using ultrasound, it begins to vibrate – but only at the corners. Credit: ETH Zürich
ETH physicists have developed a silicon wafer that behaves like a topological insulator when stimulated using ultrasound. They have thereby succeeded in turning an abstract theoretical concept into a macroscopic product.


The usual procedure goes like this: you have a complex physical system and attempt to explain its behaviour through as simple a model as possible. Sebastian Huber, Assistant Professor at the Institute for Theoretical Physics, has shown that this procedure also works in reverse: he develops macroscopic systems that exhibit exactly the same properties predicted by theory, but which have not yet been observed at this level.
He succeeded in creating an illustrative example two and a half years ago. Together with his team, he built a mechanical device made of 270 pendulums connected by springs in such a way that the installation behaves like a topological insulator. This means that the pendulum and springs are positioned so that a vibrational excitation from the outside only moves the pendulums at the edges of the installation, but not the ones in the middle (as ETH News reported).
Vibration only in the corners
The new project, which will be published this week in the journal Nature, is also focused on a macroscopic system. This time, however, he created no large mechanical device, but a much more manageably-sized object. With his team, Huber created a 10 x 10 centimetre silicon wafer that consists of 100 small plates connected to each other via thin beams. The key aspect is that when the wafer is stimulated using ultrasound, only the plates in the corners vibrate; the other plates remain still, despite their connections.
Huber drew his inspiration for the new material from a work published around a year ago by groups from Urbana-Champaign and Princeton; the researchers presented a new theoretical approach for a second-order topological insulator. "In a conventional topological insulator, the vibrations only spread across the surface, but not inside," explains Huber. "The phenomenon is reduced by one dimension." In the case of the pendulum installation, this means that the two-dimensional arrangement led to a one-dimensional vibration pattern along the edges.
In a second-order topological insulator, however, the phenomenon is reduced by two dimensions. Accordingly, with a two-dimensional silicon wafer, the vibration no longer occurs along the edges, but only in the corners, at a zero-dimensional point. "We are the first to succeed in experimentally creating the predicted higher-order topological insulator," says Huber.


A new theoretical concept
Huber has again created something that behaves in exactly the way predicted by the theory. To solve this "inverse problem", he used a systematic process that he developed together with the group led by Chiara Daraio, now a professor at Caltech, and which he has published this week in the journal Nature Materials. Broadly speaking, Huber shows how a theoretically predicted functionality can be turned into concrete geometry. "In our example, we tested it using mechanical vibrations, by coupling elements with clearly defined modes of vibration using weak links," says Huber. "But the process can also be transferred to other applications, such as to optical or electrical systems."
Expansion to the third dimension
Huber already has clear plans for how to proceed: he wants to achieve a three-dimensional second-order topological insulator, in which the vibrations can be transmitted one-dimensionally. He recently received a Consolidator Grant from the European Research Council (ERC) for this project. Huber explains the basic idea: "We stack a number of these two-dimensional structures on top of each other, so that a three-dimensional form emerges. In this form, information or energy can be conducted from point A to point B through a one-dimensional channel."
Huber can think of a few possible applications. For example, such new topological insulators could be used to build robust and precise waveguides for communications networks. They could also be of use in the energy sector, for example for energy harvesting, in which energy from a diffuse surrounding source is focused for technological use.
Also of interest to theoreticians
Huber's results will not only be of interest to engineers and materials researchers, but also theoretical physicists. "The key finding from a theoretical viewpoint is that certain second-order topological insulators cannot be mathematically described as a dipole, as conventional topological insulators are, but as quadrupoles, which are far more complex," explains Huber. "The fact that we have been able to implement this experimentally in a macroscopic structure for the first time is therefore also a breakthrough for theoreticians."
[Image: 1x1.gif] Explore further: Soundproofing with quantum physics
More information: Marc Serra-Garcia et al. Observation of a phononic quadrupole topological insulator, Nature (2018). DOI: 10.1038/nature25156
Kathryn H. Matlack et al. Designing perturbative metamaterials from discrete models, Nature Materials (2018). DOI: 10.1038/s41563-017-0003-3

Journal reference: Nature [Image: img-dot.gif] [Image: img-dot.gif] Nature Materials [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: ETH Zurich


Read more at: https://phys.org/news/2018-01-quantum-ph...y.html#jCp

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#79
This sounds like that idle executive desktop toy
that has ~5 suspended ball bearings.
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#80
(01-19-2018, 04:14 PM)Kalter Rauch Wrote: This sounds like that idle executive desktop toy
that has ~5 suspended ball bearings.

Do you mean ,The one that goes... :




Topologically insulated from the waves and central (D.C.) vortice of a draining swamp?
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#82
'Two-way signaling' possible with a single quantum particle
February 26, 2018 by Lisa Zyga, Phys.org feature


[Image: twowaycommun.jpg]
For two partners to both communicate using a single quantum particle, the particle is prepared in a superposition of two locations. When each part of the particle is sent to the partner, the particle hits a unitary device, which guides the particle in such a way that both partners get the message that has been sent to them. Credit: Del Santo and Dakić. ©2018 American Physical Society
Classically, information travels in one direction only, from sender to receiver. In a new paper, however, physicists Flavio Del Santo at the University of Vienna and Borivoje Dakić at the Austrian Academy of Sciences have shown that, in the quantum world, information can travel in both directions simultaneously—a feature that is forbidden by the laws of classical physics.


In classical communication, such as email, text message, or phone call, a message is embedded in an information carrier, such as a particle or signal, that travels in only one direction at a time. In order to communicate in the other direction using the same information carrier, it is necessary to wait until the particle arrives at the receiver and then send the particle back to the sender. In other words, it is classically impossible to perform two-way communication by using the single exchange of a single particle.
However, this is exactly what Del Santo and Dakić theoretically show. To do this, they use a quantum particle that has been put in a superposition of two different locations. As the physicists explain, being in a quantum superposition means that the quantum particle is "simultaneously present" at each partner's location. Therefore, both partners are able to encode their messages into a single quantum particle simultaneously, a task that is essentially impossible using classical physics.
"Consider the simplest scenario, where two players, Alice and Bob, want to exchange a simple bit of information, i.e., either 0 or 1," Dakić explained to Phys.org. "They encode their respective bits (messages) at the same time, directly into the superposition state of a quantum particle. Once the information is encoded, the partners send their 'parts of quantum particle' towards each other.
Positioned halfway in between Alice and Bob is a unitary device, which may be experimentally implemented by, for example, a beam splitter.
"Conditioned on the messages that the particle carries, when the particle hits the unitary device, it bounces back either to Alice or Bob deterministically," Dakić said. "More precisely, the unitary device guides the particle a 'smart way,' such that, at the end both Alice and Bob get the bit (message) that has been sent to them. For example, if the particle ends up with Alice, she would know that the Bob's bit was just opposite from her bit, and vice versa."
So in the end, both players send and receive a message—all within the same amount of time it would take to send a one-way message using a classical particle.
These theoretical results have already been verified by a new experiment using single photons, reported by Del Santo, Dakić, and their coauthors. The experimental results further strengthen the new concept by showing that the communication is secure and anonymous. In particular, the direction of communication is hidden—an eavesdropper cannot tell who is the sender and who is the receiver. Consequently, the results may lead to improvements in quantum communication that has advantages in terms of both speed and security.
[Image: 1x1.gif] Explore further: Researchers chart the 'secret' movement of quantum particles
More information: Flavio Del Santo and Borivoje Dakić. "Two-Way Communication with a Single Quantum Particle." Physical Review Letters. DOI: 10.1103/PhysRevLett.120.060503. Also at arXiv:1706.08144 [quant-ph]

Journal reference: Physical Review Letters


Read more at: https://phys.org/news/2018-02-two-way-qu...e.html#jCp

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#83
...Right where I Sheep Eye  Left Off...

Recurrences in an isolated quantum many-body system
February 23, 2018, Vienna University of Technology


[Image: quantumrecur.jpg]
Recurrence can be demonstrated with balls in a box: when they start out in an ordered state, they will become more disordered. But at some point, they will return to the initial state -- it just might take a while. Credit: TU Wien
It is one of the most astonishing results of physics—when a complex system is left alone, it will return to its initial state with almost perfect precision. Gas particles, for example, chaotically swirling around in a container, will return almost exactly to their starting positions after some time. The Poincaré Recurrence Theorem is the foundation of modern chaos theory. For decades, scientists have investigated how this theorem can be applied to the world of quantum physics. Now, researchers at TU Wien (Vienna) have successfully demonstrated a kind of Poincaré recurrence in a multi-particle quantum system. The results have been published in the journal Science.



At the end of the 19th century, the French scientist Henri Poincaré studied systems that cannot be fully analysed with perfect precision—for example, solar systems consisting of many planets and asteroids, or gas particles that keep bumping into each other. His surprising result: Every state that is physically possible will be occupied by the system at some point—at least to a very good degree of approximation. If we just wait long enough, at some point all planets will form a straight line, just by coincidence. The gas particles in a box will create interesting patterns, or go back to the state in which they were when the experiment started.

A similar theorem can be proved for quantum systems. There, however, completely different rules apply: "In quantum physics, we have to come up with a completely new way of addressing this problem," says Professor Jörg Schmiedmayer from the Institute for Atomic and Subatomic Physics at TU Wien. "For very fundamental reasons, the state of a large quantum system, consisting of many particles, can never be perfectly measured. Apart from that, the particles cannot be seen as independent objects, we have to take into account that they are quantum mechanically entangled."

[Image: 1-quantumrecur.jpg]
The atom chip, used to control ultra cold atom clouds. Credit: TU Wien
There have been attempts to demonstrate the effect of "Poincaré recurrence" in quantum systems, but until now this has only been possible with a very small number of particles, whose state was measured as precisely as possible. This is extremely complicated and the time it takes the system to return to its original state increases dramatically with the number of particles. Jörg Schmiedmayers team at TU Wien, however, chose a different approach: "We are not so much interested in the complete inner state of the system, which cannot be measured anyway," says Bernhard Rauer, first author of the publication. "Instead we want to ask: which quantities can we observe, that tell us something interesting about the system as a whole? And are there times at which these collective quantities return to their initial value?"

 

The team studied the behaviour of an ultracold gas, consisting of thousands of atoms, which is kept in place by electromagnetic fields on a chip. "There are several different quantities describing the characteristics of such a quantum gas—for example coherence lengths in the gas and correlation functions between different points in space. These parameters tell us, how closely the particles are linked by quantum mechanical effects," says Sebastian Erne, who was responsible for the theoretical calculations necessary for the project. "Our everyday intuition is not used to dealing with these quantities, but for a quantum systems, they are crucial."

Recurrence Discovered—in Collective Quantities

By measuring such quantities, which do not refer to single particles, but characterize the system as a whole, it was indeed possible to observe the long-sought quantum recurrence. And not only that: "With our atom chip, we can even influence the time it takes the system to return to one particular state," says Jörg Schmiedmayer. "By measuring this kind of recurrence, we learn a lot about the collective dynamics of the atoms—for example about the speed of sound in the gas or about scattering phenomena of density waves."

The old question, whether quantum systems show recurrences, can finally be answered: Yes, they do—but the concept of recurrence has to be slightly redefined. Instead of trying to map out the complete inner quantum state of a system, which cannot be measured anyway, it makes more sense to concentrate on quantities which can be measured in quantum experiments. These quantities can be observed to drift away from their initial value—and to return to their initial state eventually.

[Image: 1x1.gif] Explore further: Testing quantum field theory in a quantum simulator

More information: Bernhard Rauer et al, Recurrences in an isolated quantum many-body system, Science (2018). DOI: 10.1126/science.aan7938


Journal reference: Science [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: Vienna University of Technology


Read more at: https://phys.org/news/2018-02-recurrence...y.html#jCp
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#84
Unlocking the secrets of the universe
February 28, 2018, Arizona State University


[Image: 1-unlockingthe.jpg]
This artist's rendering shows the universe's first, massive, blue stars embedded in gaseous filaments, with the cosmic microwave background just visible at the edges. Using radio observations of the distant universe, NSF-funded researchers Judd Bowman of Arizona State University, Alan Rogers of MIT and their colleagues discovered the influence of such early stars on primordial gas. Although they can't directly see the light from the massive stars, Bowman's team was able to infer their presence from dimming of the cosmic microwave background (CMB), a result of the gaseous filaments absorbing the stars' UV light. The CMB is dimmer than expected, indicating that the filaments may have been colder than expected, possibly from interactions with dark matter. Credit: N.R.Fuller, National Science Foundation

Long ago, about 400,000 years after the beginning of the universe (the Big Bang), the universe was dark. There were no stars or galaxies, and the universe was filled primarily with neutral hydrogen gas.

Then, for the next 50-100 million years, gravity slowly pulled the densest regions of gas together until ultimately the gas collapsed in some places to form the first stars.
What were those first stars like and when did they form? How did they affect the rest of the universe? These are questions astronomers and astrophysicists have long pondered.
Now, after 12 years of experimental effort, a team of scientists, led by ASU School of Earth and Space Exploration astronomer Judd Bowman, has detected the fingerprints of the earliest stars in the universe. Using radio signals, the detection provides the first evidence for the oldest ancestors in our cosmic family tree, born by a mere 180 million years after the universe began.
"There was a great technical challenge to making this detection, as sources of noise can be a thousand times brighter than the signal - it's like being in the middle of a hurricane and trying to hear the flap of a hummingbird's wing." says Peter Kurczynski, the National Science Foundation program officer who supported this study. "These researchers with a small radio antenna in the desert have seen farther than the most powerful space telescopes, opening a new window on the early universe."
[Image: 3-unlockingthe.jpg]
In each instrument, radio waves are collected by an antenna consisting of two rectangular metal panels mounted horizontally on fiberglass legs above a metal mesh. The EDGES detection required the radio quietness at the Murchison Radio-astronomy Observatory, as Australian national legislation limits the use of radio transmitters near the site. This discovery sets the stage for follow-up observations with other powerful low-frequency facilities, including HERA and the forthcoming SKA-low. Credit: CSIRO Australia
Radio Astronomy
To find these fingerprints, Bowman's team used a ground-based instrument called a radio spectrometer, located at the Australia's national science agency (CSIRO) Murchison Radio-astronomy Observatory (MRO) in Western Australia. Through their Experiment to Detect the Global EoR Signature (EDGES), the team measured the average radio spectrum of all the astronomical signals received across most of the southern-hemisphere sky and looked for small changes in power as a function of wavelength (or frequency).
As radio waves enter the ground-based antenna, they are amplified by a receiver, and then digitized and recorded by computer, similar to how FM radio receivers and TV receivers work. The difference is that the instrument is very precisely calibrated and designed to perform as uniformly as possible across many radio wavelengths.

The signals detected by the radio spectrometer in this study came from primordial hydrogen gas that filled the young universe and existed between all the stars and galaxies. These signals hold a wealth of information that opens a new window on how early stars - and later, black holes, and galaxies - formed and evolved.
"It is unlikely that we'll be able to see any earlier into the history of stars in our lifetimes," says Bowman. "This project shows that a promising new technique can work and has paved the way for decades of new astrophysical discoveries."
This detection highlights the exceptional radio quietness of the MRO, particularly as the feature found by EDGES overlaps the frequency range used by FM radio stations. Australian national legislation limits the use of radio transmitters within 161.5 miles (260 km) of the site, substantially reducing interference which could otherwise drown out sensitive astronomy observations.
The results of this study have been recently published in Nature by Bowman, with co-authors Alan Rogers of the Massachusetts Institute of Technology's Haystack Observatory, Raul Monsalve of the University of Colorado, and Thomas Mozdzen and Nivedita Mahesh also of ASU's School of Earth and Space Exploration.
[Image: 2-unlockingthe.jpg]
A timeline of the universe, updated to show when the first stars emerged. This updated timeline of the universe reflects the recent discovery that the first stars emerged by 180 million years after the Big Bang. The research behind this timeline was conducted by Judd Bowman of Arizona State University and his colleagues, with funding from the National Science Foundation. Credit: N.R.Fuller, National Science Foundation
Unexpected results
The results of this experiment confirm the general theoretical expectations of when the first stars formed and the most basic properties of early stars.
"What's happening in this period," says co-author Rogers of MIT's Haystack Observatory, "is that some of the radiation from the very first stars is starting to allow hydrogen to be seen. It's causing hydrogen to start absorbing the background radiation, so you start seeing it in silhouette, at particular radio frequencies. This is the first real signal that stars are starting to form, and starting to affect the medium around them."
The team originally tuned their instrument to look later in cosmic time, but in 2015 decided to extend their search. "As soon as we switched our system to this lower range, we started seeing things that we felt might be a real signature," Rogers says. "We see this dip most strongly at about 78 megahertz, and that frequency corresponds to roughly 180 million years after the Big Bang," Rogers says. "In terms of a direct detection of a signal from the hydrogen gas itself, this has got to be the earliest."
The study also revealed that gas in the universe was probably much colder than expected (less than half the expected temperature). This suggests that either astrophysicists' theoretical efforts have overlooked something significant or that this may be the first evidence of non-standard physics: Specifically, that baryons (normal matter) may have interacted with dark matter and slowly lost energy to dark matter in the early universe, a concept that was originally proposed by Rennan Barkana of Tel Aviv University.

When did the first stars light up the universe? Credit: National Science Foundation

"If Barkana's idea is confirmed," says Bowman, "then we've learned something new and fundamental about the mysterious dark matter that makes up 85 percent of the matter in the universe, providing the first glimpse of physics beyond the standard model."
The next steps in this line of research are for another instrument to confirm this team's detection and to keep improving the performance of the instruments, so that more can be learned about the properties of early stars. "We worked very hard over the last two years to validate the detection," says Bowman, "but having another group confirm it independently is a critical part of the scientific process."
Bowman would also like to see an acceleration of efforts to bring on new radio telescopes like the Hydrogen Epoch of Reionization Array (HERA) and the Owens Valley Long Wavelength Array (OVRO-LWA).
"Now that we know this signal exists," says Bowman, "we need to rapidly bring online new radio telescopes that will be able to mine the signal much more deeply."
The antennas and portions of the receiver used in this experiment were designed and constructed by Rogers and the MIT Haystack Observatory team. The ASU team and Monsalve added the automated antenna reflection measurement system to the receiver, outfitted the control hut with the electronics, constructed the ground plane and conducted the field work for the project. The current version of EDGES is the result of years of design iteration and ongoing detailed technical refinement of the calibration instrumentation to reach the levels of precision necessary for successfully achieving this difficult measurement.
[Image: 1x1.gif] Explore further: MWA radio telescope expansion complete—Exploration of the universe's first stars begins
More information: Judd D. Bowman et al. An absorption profile centred at 78 megahertz in the sky-averaged spectrum, Nature (2018). DOI: 10.1038/nature25792
Rennan Barkana. Possible interaction between baryons and dark-matter particles revealed by the first stars, Nature (2018). DOI: 10.1038/nature25791

Journal reference: Nature
Provided by: Arizona State University


Read more at: https://phys.org/news/2018-02-secrets-universe.html#jCp

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[url=https://phys.org/news/2018-03-trapped-ion-blocks-quantum.html][Image: 5763a9466fe23.jpg]

New speed record for trapped-ion 'building blocks' of quantum computers
Researchers at Oxford University have set a new speed record for the 'logic gates' that form the building blocks of quantum computing - a technology that could transform the way we process information.
[Image: 1x1.gif]1 hour ago in Quantum Physics 



[Image: theshapeofth.jpg]
The shape of things to come for quantum materials?
For the first time, researchers isolated and characterized atomically thin 2-D crystals of pentagons bonded together in palladium diselenide (PdSe2). The research confirmed predictions that the puckered structure would be ...
[Image: 1x1.gif]2 hours ago in Nanomaterials


[Image: 2-experimental.jpg]
Experimentally demonstrated a toffoli gate in a semiconductor three-qubit system
A new progress in the scaling of semiconductor quantum dot-based qubits has been achieved b y researchers at the University of Science and Technology of China. Professor GUO Guoping with his co-workers, XIAO Ming, LI Haiou ...
[Image: 1x1.gif]4 hours ago in Quantum Physics
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#85
China's launch of quantum satellite major step in space race

August 16, 2016 by Nomaan Merchant
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[Image: chinaslaunch.jpg]

In this photo released by China's Xinhua News Agency, a Long March-2D rocket carrying the world's first quantum satellite lifts off from the Jiuquan Satellite Launch Center in Jiuquan, northwestern China's Gansu Province, early Tuesday, …[url=https://phys.org/news/2016-08-china-quantum-satellite-major-space.html]more

China's launch of the first quantum satellite Tuesday will push forward efforts to develop the ability to send communications that can't be penetrated by hackers, experts said.

The satellite launched into space from the Jiuquan launch base in northwestern China's Gobi desert will allow Chinese researchers to transmit test messages between Beijing and northwestern China as well as other locations around the world.

If the tests are successful, China will take a major step toward building a worldwide network that can send messages that can't be wiretapped or cracked through conventional methods.

"It moves the challenge for an eavesdropper to a different domain," said Alexander Ling, principal investigator at the Centre for Quantum Technologies in Singapore. "Lots of people around the world think having secure communications at a quantum level is important. The Europeans, the Americans had the lead, but now the Chinese are showing the way forward."

Quantum communications use subatomic particles to securely communicate between two points. A hacker trying to crack the message changes its form in a way that would alert the sender and cause the message to be altered or deleted.

Researchers around the world have successfully sent quantum messages by land. But a true satellite-based network would make it possible to send quickly encrypted messages in an instant around the world and open the door to other possible uses of the technology.

Cybersecurity has been a major focus in recent years for China, which has pushed regulations aimed at limiting technology imported from the U.S. in the wake of Edward Snowden's revelations of widespread surveillance by the U.S. through the use of American hardware.


China has in turn been repeatedly accused by the U.S. of hacking into computer systems to steal commercial secrets and information that could harm American national security. China has rejected claims that it runs a state-sponsored hacking program and says that it is among the leading victims of cybercrime.


Quantum messaging could become a major defense against hackers and have applications ranging from military and government communications to online shopping.

The biggest challenge, Ling said, is being able to orient the satellite with pinpoint accuracy to a location on Earth where it can send and receive data without being affected by any disturbances in Earth's atmosphere. The results of China's tests will be closely watched by other research teams, he said.


"It's very difficult to point the satellite accurately," Ling said. "You're trying to send a beam of light from a satellite that's 500 kilometers (310 miles) above you."

Hoi Fung Chau, a professor and quantum communications researcher at Hong Kong University, said that it was too soon to say if the tests will succeed, but added he expected quantum messages by satellite to become the global standard eventually.

"The theory is already there, the technology is almost there," he said. "It's just a matter of time."

The launch is a major triumph for China, which has spent years researching quantum technology and developing the satellite and other uses for it. China has previously announced the construction of a quantum link between Beijing and Shanghai that would be used by government agencies and banks.

Pan Jianwei, chief scientist on the satellite project, was quoted by the official Xinhua News Agency as saying the launch proved China was no longer a follower in information technology, but "one of the leaders guiding future IT achievements."

Explore further: Quantum satellite device tests technology for global quantum network

Read more at: https://phys.org/news/2016-08-china-quan...e.html#jCp

Source: https://phys.org/news/2016-08-china-quan...space.html

---

I KNEW the Chinese had ALREADY put a 'Quatum Sateelite' into orbit.  They would NOT have launched it if they could NOT communicate with the Quatum Computer on the ground...PERIOD !!!

So while the above articles are interesting EA, are they REALLY new ?

Still Worship for finding and posting them

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#86
Quantum speed limits are not actually quantum
March 15, 2018 by Lisa Zyga, Phys.org feature


[Image: classicalspe.jpg]
Source: pixabay
Quantum mechanics has fundamental speed limits—upper bounds on the rate at which quantum systems can evolve. However, two groups working independently have published papers showing for the first time that quantum speed limits have a classical counterpart: classical speed limits. The results are surprising, as previous research has suggested that quantum speed limits are purely quantum in nature and vanish for classical systems.

Both groups—one consisting of Brendan Shanahan and Adolfo del Campo at the University of Massachusetts along with Aurelia Chenu and Norman Margolus at MIT, the other composed of Manaka Okuyama of the Tokyo Institute of Technology and Masayuki Ohzeki at Tohoku University—have published papers on classical speed limits in Physical Review Letters.

Over the past several decades, physicists have been investigating quantum speed limits, which determine the minimum time for a given process to occur in terms of the energy fluctuations of the process. A quantum speed limit can then be thought as a time-energy uncertainty relation. Although this concept is similar to Heisenberg's uncertainty principle, which relates position and momentum uncertainties, time is treated differently in quantum mechanics (as a parameter rather than an observable).

Still, the similarities between the two relations, along with the fact that Heisenberg's uncertainty principle is a strictly quantum phenomenon, have long suggested that quantum speed limits are likewise strictly quantum and have no classical counterpart. The only known limitation on the speed of classical systems is that objects may not travel faster than the speed of light due to special relativity, but this is unrelated to the energy-time relation in quantum speed limits.

The new papers show that speed limits based on a trade-off between energy and time do exist for classical systems, and in fact, that there are infinitely many of these classical speed limits. The results demonstrate that quantum speed limits are not based on any underlying quantum phenomena, but instead are a universal property of the description of any physical process, whether quantum or classical.

"It is really the notion of information and distinguishability that unifies speed limits in both the classical and quantum domains," del Campo told Phys.org.

As quantum speed limits have potential applications for understanding the ultimate limits of quantum computing, the new results may help to determine which scenarios may benefit from a quantum speedup compared to classical methods.

"Quantum speed limits have many applications, ranging from metrology to quantum computation," del Campo said. "It is exciting to imagine the implications of the classical speed limits we have derived."

[Image: 1x1.gif] Explore further: Quantum speed limit may put brakes on quantum computers

More information: B. Shanahan, A. Chenu, N. Margolus, and A. del Campo. "Quantum Speed Limits across the Quantum-to-Classical Transition." Physical Review Letters. DOI: 10.1103/PhysRevLett.120.070401. Also at arXiv:1710.07335 [quant-ph]

Manaka Okuyama and Masayuki Ohzeki. "Quantum Speed Limit is Not Quantum." Physical Review Letters. DOI: 10.1103/PhysRevLett.120.070402. Also at arXiv:1710.03498 [quant-ph]


Journal reference: Physical Review Letters


Read more at: https://phys.org/news/2018-03-quantum-limits.html#jCp
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#87
Quantum shift shows itself in coupled light and matter
April 16, 2018, Rice University


[Image: 1-quantumshift.jpg]
A simplified schematic shows the basic idea behind a Rice University experiment to detect a Bloch-Siegert shift in strongly coupled light and matter. In this illustration, a light field rotating in the opposite direction to an orbiting electron still interacts with the electron in a cavity, in this case the empty space between two mirrors. The influence of resonance on the counter-rotating element defines the shift. Credit: Xinwei Li/Kono Lab at Rice University
A team led by Rice University scientists used a unique combination of techniques to observe, for the first time, a condensed matter phenomenon about which others have only speculated. The research could aid in the development of quantum computers.



The researchers, led by Rice physicist Junichiro Kono and graduate student Xinwei Li, observed and measured what's known as a Bloch-Siegert shift in strongly coupled light and matter.

Results of the complicated combination of modeling and experimentation are the subject of a paper in Nature Photonics. The technique could lead to a greater understanding of theoretical predictions in quantum phase transitions because the experimental parameters used in the Rice experiments are highly adjustable, according to Kono. Ultimately, he said, it may help in the development of robust quantum bits for advanced computing.

The Bloch-Siegert shift, a theory born in the 1940s, is a quantum interaction in which counter-rotating fields are able to interact. But such interactions have been difficult to detect.

The theory suggested to Kono and Li that it might be possible to detect such a shift when a light field rotating in one direction strongly couples with a matter-bound electron field rotating in the opposite direction. These interactions have proven difficult to create without the unique tools assembled by the Rice-led team.

[Image: quantumshift.jpg]
Researchers at Rice University, including graduate student Xinwei Li, have observed and measured a Bloch-Siegert shift in strongly coupled light and matter in a vacuum. The project could aid in the development of quantum computers. Credit: Jeff Fitlow/Rice University
"Light and matter should not resonate with each other when they are rotating in opposite directions," Kono said. "However, in our case, we proved they can still strongly couple, or interact, even though they are not resonating with each other."

Kono and his colleagues created the resonance frequency shift in a two-level electron system induced by coupling with an electromagnetic field inside a cavity even when the electrons and field are rotating in opposite directions - a truly surprising effect that occurs only in a regime where light and matter are mixed together to an extreme degree.

In this case, the levels are those of two-dimensional electrons in solid gallium arsenide in a strong perpendicular magnetic field. They hybridize with the "vacuum" electromagnetic field in the cavity to form quasiparticles known as polaritons. This vacuum-matter hybridization had been expected to lead to a finite frequency shift, a vacuum Bloch-Siegert shift, in optical spectra for circularly polarized light counter-rotating with the electrons. The Rice team can now measure it.

 

"In condensed matter physics, we often look for new ground states (lowest-energy states). For that purpose, light-matter coupling is usually considered an enemy because light drives matter to an excited (higher-energy) state," Kono said. "Here we have a unique system that is predicted to go into a new ground state because of strong light-matter coupling. Our technique will help us know when the strength of light-matter coupling exceeds a certain threshold."

The research builds upon a strong vacuum field-matter coupling in a high-quality-factor cavity the lab first created and reported in 2016. The results at the time only hinted at the presence of a Bloch-Siegert shift. "Experimentally, we just demonstrated the new regime," Li said. "But here, we have a very deep understanding of the physics involved."



Kono and Li credited physicist Motoaki Bamba of Osaka University for providing a theoretical basis for the discovery and Katsumasa Yoshioka of Yokohama National University and a former visiting scholar at Rice for providing a device to produce circularly polarized light in the terahertz range of the electromagnetic spectrum.

The lab used the light to probe the shift in an ultra-high quality, two-dimensional electron gas supplied by Purdue University physicist Michael Manfra and set in a gallium arsenide quantum well (to contain the particles) under the influence of a strong magnetic field and low temperature. A terahertz spectroscope measured activity in the system.

"Linearly polarized light means an alternating current electric field that is always oscillating in one direction," Kono said. "In circularly polarized light, the electric field is rotating." That allowed the researchers to distinguish between left- and right-rotating electrons in their vacuum-bound condensed matter in a magnetic field, and from that, measure the shift.

"In this work, both theoretically and experimentally, we demonstrated that even though the electron is rotating this way and the light is rotating (the other) way, they still strongly interact with each other, which leads to a finite frequency shift known as the Bloch-Siegert shift," Kono said.

Observing the shift is a direct indication that ultra-strong light-matter coupling invalidated the rotating wave approximation, he said. "That approximation is behind almost all light-matter interaction phenomenon, including lasers, nuclear magnetic resonance and quantum computing," Kono said. "In any resonant light-matter interaction, people are satisfied with this approximation, because the coupling is usually weak. But if the coupling between light and matter is strong, it doesn't work. That's clear evidence that we are in the ultra-strong coupling regime."

[Image: 1x1.gif] Explore further: Light and matter merge in quantum coupling

More information: Xinwei Li et al, Vacuum Bloch–Siegert shift in Landau polaritons with ultra-high cooperativity, Nature Photonics (2018). DOI: 10.1038/s41566-018-0153-0


Journal reference: Nature Photonics [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: Rice University


Read more at: https://phys.org/news/2018-04-quantum-sh...d.html#jCp
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#88
For wook. Angel
Qubit Sheep QuTRIT

Quote:Physically, entangled particles cannot be described as individual particles with defined states, but only as a single system.
single system=entanglement / 3 =.3333.... Holycowsmile


Stronger-than-binary correlations experimentally demonstrated for the first time
May 21, 2018 by Lisa Zyga, Phys.org feature


[Image: strongerthan.jpg]
Two possible explanations for the quantum measurement process: (a) A binary measurement that generates the final outcome in two steps (first ruling out one of the three outcomes, then selecting between the two remaining outcomes), or (b) a …more
For the first time, physicists have experimentally demonstrated ternary—rather than binary—quantum correlations between entangled objects. The results show that the quantum measurement process cannot be described as a binary process (having two possible outcomes), but rather stronger-than-binary ternary measurements (which have three possible outcomes) should be considered in order to fully understand how the quantum measurement process works.



The physicists, Xiao-Min Hu and coauthors from China, Germany, Spain, and Hungary, have published a paper on the stronger-than-binary correlations in a recent issue of Physical Review Letters.

"We discovered and experimentally verified the existence of genuine ternary measurements," coauthor Matthias Kleinmann at the University of Siegen in Siegen, Germany, and the University of the Basque Country in Bilbao, Spain, told Phys.org. "The experimental conclusions are independent of any underlying theory (here: quantum theory) and establish that ternary measurements are a generic feature of nature."

Before now, stronger-than-binary correlations have been theoretically predicted to exist, but this is the first time that they have been experimentally observed. In their experiments, the researchers entangled two photonic qutrits, each of which has three possible states (0, 1, and 2), instead of just two (0 and 1) as for qubits. They then sent the qutrits to different laboratories where they measured the state of each qutrit, enabling them to determine the strength of the correlations between the two qutrits.

[Image: 1-strongerthan.jpg]
Illustration of the experimental setup for demonstrating ternary correlations. Credit: Hu et al. ©2018 American Physical Society
If the quantum measurement process were binary, then measurements could be described as a two-step process in which first one of the three possible measurement outcomes is ruled out by a classical mechanism, and then a quantum binary measurement selects between the two remaining outcomes. In this binary measurement process, the maximum correlation between two entangled objects cannot exceed a certain value.

In their experiments, the researchers demonstrated that the strength of the correlations between the entangled qutrits exceed this maximum value. To do this, they performed a Bell-type experiment in which they showed that the observed correlations violate the maximum inequality for nonsignalling binary correlations with a very high statistical significance, corresponding to 9.3 standard deviations. The results imply that the measurement process in quantum theory cannot be explained by the two-step process with binary measurements. Instead, the measurement process here is genuinely ternary, where the quantum ternary measurement selects between all three of the possible states at once.

Overall, the researchers explain that the observations of stronger-than-binary correlations don't contradict previous experimental evidence of binary correlations, but add new possibilities for how the quantum measurement process works at the most fundamental level.

"Now that we have established the theoretical tools and the experimental methods to understand and create ternary correlations, we aim to proceed in two directions," Kleinmann said. "First, we hope for technological applications (for example, in randomness extraction) and second, we are now using our results as a new basis for a deeper understanding of quantum theory."

[Image: 1x1.gif] Explore further: New quantum probability rule offers novel perspective of wave function collapse

More information: More information: Xiao-Min Hu et al. "Observation of Stronger-than-Binary Correlations with Entangled Photonic Qutrits." Physical Review Letters. DOI: 10.1103/PhysRevLett.120.180402 , Also at arXiv:1712.06557 [quant-ph]


Journal reference: Physical Review Letters


Read more at: https://phys.org/news/2018-05-stronger-t...y.html#jCp




Turning entanglement upside down
May 21, 2018, University of Innsbruck


[Image: entanglement.jpg]
Credit: CC0 Public Domain
A team of physicists from ICTP-Trieste and IQOQI-Innsbruck has come up with a surprisingly simple idea to investigate quantum entanglement of many particles. Instead of digging deep into the properties of quantum wave functions, which are notoriously hard to experimentally access, they propose to realize physical systems governed by the corresponding entanglement Hamiltonians. By doing so, entanglement properties of the original problem of interest become accessible via well-established tools.



Quantum entanglement forms the heart of the second quantum revolution: it is a key characteristic used to understand forms of quantum matter, and a key resource for present and future quantum technologies. Physically, entangled particles cannot be described as individual particles with defined states, but only as a single system. Even when the particles are separated by a large distance, changes in one particle also instantaneously affect the other particle(s). The entanglement of individual particles—whether photons, atoms or molecules—is part of everyday life in the laboratory today. In many-body physics, following the pioneering work of Li and Haldane, entanglement is typically characterized by the so-called entanglement spectrum: it is able to capture essential features of collective quantum phenomena, such as topological order, and at the same time, it allows to quantify the 'quantumness' of a given state—that is, how challenging it is to simply write it down on a classical computer.

Despite its importance, the experimental methods to measure the entanglement spectrum quickly reach their limits—until today, these spectra have been measured only in few qubits systems. With an increasing number of particles, this effort becomes hopeless as the complexity of current techniques increases exponentially.

"Today, it is very hard to perform an experiment beyond few particles that allows us to make concrete statements about entanglement spectra," explains Marcello Dalmonte from the International Centre for Theoretical Physics (ICTP) in Trieste, Italy. Together with Peter Zoller and Benoît Vermersch at the University of Innsbruck, he has now found a surprisingly simple way to investigate quantum entanglement directly. The physicists turn the concept of quantum simulation upside down by no longer simulating a certain physical system in the quantum simulator, but directly simulating its entanglement Hamiltonian operator, whose spectrum of excitations immediately relates to the entanglement spectrum.

"Instead of simulating a specific quantum problem in the laboratory and then trying to measure the entanglement properties, we propose simply turning the tables and directly realizing the corresponding entanglement Hamiltonian, which gives immediate and simple access to entanglement properties, such as the entanglement spectrum," explains Marcello Dalmonte. "Probing this operator in the lab is conceptually and practically as easy as probing conventional many-body spectra, a well-established lab routine."

Furthermore, there are hardly any limits to this method with regard to the size of the quantum system. This could also allow the investigation of entanglement spectra in many-particle systems, which is notoriously challenging to address with classical computers. Dalmonte, Vermersch and Zoller describe the radically new method in a current paper in Nature Physics and demonstrate its concrete realization on a number of experimental platforms, such as atomic systems, trapped ions and also solid-state systems based on superconducting quantum bits.

[Image: 1x1.gif] Explore further: Researchers create a quantum entanglement between two physically separated ultra-cold atomic clouds

More information: M. Dalmonte et al, Quantum simulation and spectroscopy of entanglement Hamiltonians, Nature Physics (2018). DOI: 10.1038/s41567-018-0151-7


Journal reference: Nature Physics [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: University of Innsbruck


Read more at: https://phys.org/news/2018-05-entangleme...e.html#jCp
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"...experimental setup for demonstrating ternary correlations..."

_________________________________________________

"The most merciful thing in this world is the inability of the human mind to correlate all its contents."
                                         
                                                                                                                         HP Lovecraft
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"...experimental setup for demonstrating ternary correlations..."
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Can a quantum drum vibrate and stand still at the same time?
May 18, 2018 by Hayley Dunning, Imperial College London


[Image: canaquantumd.jpg]
The first quantum drum test. Credit: Imperial College London
Researchers have studied how a 'drumstick' made of light could make a microscopic 'drum' vibrate and stand still at the same time.



A team of researchers from the UK and Australia have made a key step towards understanding the boundary between the quantum world and our everyday classical world.

Quantum mechanics is truly weird. Objects can behave like both particles and waves, and can be both here and there at the same time, defying our common sense. Such counterintuitive behaviour is typically confined to the microscopic realm and the question "why don't we see such behaviour in everyday objects?" challenges many scientists today.

Now, a team of researchers have developed a new technique to generate this type of quantum behaviour in the motion of a tiny drum just visible to the naked eye. The details of their research are published today in New Journal of Physics.

Project principal investigator, Dr. Michael Vanner from the Quantum Measurement Lab at Imperial College London, said: "Such systems offer significant potential for the development of powerful new quantum-enhanced technologies, such as ultra-precise sensors, and new types of transducers.

"Excitingly, this research direction will also enable us to test the fundamental limits of quantum mechanics by observing how quantum superpositions behave at a large scale."

Mechanical vibrations, such as those that create the sound from a drum, are an important part of our everyday experience. Hitting a drum with a drumstick causes it to rapidly move up and down, producing the sound we hear.

In the quantum world, a drum can vibrate and stand still at the same time. However, generating such quantum motion is very challenging. lead author of the project Dr. Martin Ringbauer from the University of Queensland node of the Australian Research Council Centre for Engineered Quantum Systems, said: "You need a special kind of drumstick to make such a quantum vibration with our tiny drum."

In recent years, the emerging field of quantum optomechanics has made great progress towards the goal of a quantum drum using laser light as a type of drumstick. However, many challenges remain, so the authors' present study takes an unconventional approach.

Dr. Ringbauer continues: "We adapted a trick from optical quantum computing to help us play the quantum drum. We used a measurement with single particles of light—photons—to tailor the properties of the drumstick.

"This provides a promising route to making a mechanical version of Schrodinger's cat, where the drum vibrates and stands still at the same time."

These experiments have made the first observation of mechanical interferences fringes, which is a crucial step forward for the field.

In the experiment, the fringes were at a classical level due to thermal noise, but motivated by this success, the team are now working hard to improve their technique and operate the experiments at temperatures close to absolute zero where quantum mechanics is expected to dominate.

These future experiments may reveal new intricacies of quantum mechanics and may even help light the path to a theory that links the quantum world and the physics of gravity.

[Image: 1x1.gif] Explore further: Quantum speed limits are not actually quantum

More information: 'Generation of Mechanical Interference Fringes by Multi-Photon Counting' by M Ringbauer, T J Weinhold, L A Howard, A G White & M R Vanner is published in New Journal of Physics 20, 053042 (2018) DOI: 10.1088/1367-2630/aabb8d


Journal reference: New Journal of Physics [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: Imperial College London


Read more at: https://phys.org/news/2018-05-quantum-vibrate.html#jCp



Life beats to the same quantum drum as non - living matter!!!
LilD  Sheep    Holycowsmile

 Quantum effects observed in photosynthesis
May 21, 2018, University of Groningen


[Image: quantumeffec.jpg]
The figure shows the photosynthetic complex of light-harvesting green sulfur bacteria the green and yellow circles highlight the two molecules simultaneously excited. Credit: dr. Thomas la Cour Jansen/University of Groningen
Molecules that are involved in photosynthesis exhibit the same quantum effects as non-living matter, concludes an international team of scientists including University of Groningen theoretical physicist Thomas la Cour Jansen. This is the first time that quantum mechanical behavior was proven to exist in biological systems that are involved in photosynthesis. The interpretation of these quantum effects in photosynthesis may help in the development of nature-inspired light-harvesting devices. The results were published in Nature Chemistry on 21 May.



For several years now, there has been a debate about quantum effects in biological systems. The basic idea is that electrons in can be in two states at once, until they are observed. This may be compared to the thought experiment known as Schrödinger's Cat. The cat is locked in a box with a vial of a toxic substance. If the cap of the vial is locked with a quantum system, it may simultaneously be open or closed, so the cat is in a mixture of the states "dead" and "alive," until we open the box and observe the system. This is precisely the apparent behavior of electrons.

Vibrations

In earlier research, scientists had already found signals suggesting that light-harvesting molecules in bacteria may be excited into two states simultaneously. In itself this proved the involvement of quantum mechanical effects, however in those experiments, that excited state supposedly lasted more than 1 picosecond (0.000 000 000 001 second). This is much longer than one would expect on the basis of quantum mechanical theory.

Jansen and his colleagues show in their publication that this earlier observation is wrong. "We have shown that the quantum effects they reported were simply regular vibrations of the molecules." Therefore, the team continued the search. "We wondered if we might be able to observe that Schrödinger cat situation."

Superposition

They used different polarizations of light to perform measurements in light-harvesting green sulfur bacteria. The bacteria have a photosynthetic complex, made up of seven light sensitive molecules. A photon will excite two of those molecules, but the energy is superimposed on both. So just like the cat is dead or alive, one or the other molecule is excited by the photon. "In the case of such a superposition, spectroscopy should show a specific oscillating signal," explains Jansen. "And that is indeed what we saw. Furthermore, we found quantum effects that lasted precisely as long as one would expect based on theory and proved that these belong to energy superimposed on two molecules simultaneously." Jansen concludes that biological systems exhibit the same quantum effects as non-biological systems.

The observation techniques developed for this research project may be applied to different systems, both biological and non-biological. Jansen is happy with the results. "This is an interesting observation for anyone who is interested in the fascinating world of quantum mechanics. Moreover, the results may play a role in the development of new systems, such as the storage of solar energy or the development of quantum computers."

 Explore further: Purple bacteria shine path to super-efficient light harvesting

More information: Erling Thyrhaug et al, Identification and characterization of diverse coherences in the Fenna–Matthews–Olson complex, Nature Chemistry (2018). DOI: 10.1038/s41557-018-0060-5


Journal reference: Nature Chemistry [/url]
Provided by: [url=https://phys.org/partners/university-of-groningen/]University of Groningen



Read more at: https://phys.org/news/2018-05-quantum-ef...s.html#jCp
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Superconducting metamaterial traps quantum light
September 27, 2018 by Robert Perkins, California Institute of Technology


[Image: 10-superconduct.jpg]
A superconducting metamaterial chip mounted into a microwave test package. The purplish-violet reflection in the center is an optical effect that can seen by the naked eye, and is the result of the diffaction of light by the periodic …more
Conventional computers store information in a bit, a fundamental unit of logic that can take a value of 0 or 1. Quantum computers rely on quantum bits, also known as a "qubits," as their fundamental building blocks. Bits in traditional computers encode a single value, either a 0 or a 1. The state of a qubit, by contrast, can simultaneously have a value of both 0 and 1. This peculiar property, a consequence of the fundamental laws of quantum physics, results in the dramatic complexity in quantum systems. 



Quantum computing is a nascent and rapidly developing field that promises to use this complexity to solve problems that are difficult to tackle with conventional computers. A key challenge for quantum computing, however, is that it requires making large numbers of qubits work together—which is difficult to accomplish while avoiding interactions with the outside environment that would rob the qubits of their quantum properties. 

New research from the lab of Oskar Painter, John G Braun Professor of Applied Physics and Physics in the Division of Engineering and Applied Science, explores the use of superconducting metamaterials to overcome this challenge. 

Metamaterials are specially engineered by combining multiple component materials at a scale smaller than the wavelength of light, giving them the ability to manipulate how particles of light, or photons, behave. Metamaterials can be used to reflect, turn, or focus beams of light in nearly any desired manner. A metamaterial can also create a frequency band where the propagation of photons becomes entirely forbidden, a so-called "photonic bandgap." 

The Caltech team used a photonic bandgap to trap microwave photons in a superconducting quantum circuit, creating a promising technology for building future quantum computers.

"In principle, this is a scalable and flexible substrate on which to build complex circuits for interconnecting certain types of qubits," says Painter, leader of the group that conducted the research, which was published in Nature Communications on September 12. "Not only can one play with the spatial arrangement of the connectivity between qubits, but one can also design the connectivity to occur only at certain desired frequencies."

Painter and his team created a quantum circuit consisting of thin films of a superconductor—a material that transmits electric current with little to no loss of energy—traced onto a silicon microchip. These superconducting patterns transport microwaves from one part of the microchip to another. What makes the system operate in a quantum regime, however, is the use of a so-called Josephson junction, which consists of an atomically thin non-conductive layer sandwiched between two superconducting electrodes. The Josephson junction creates a source of microwave photons with two distinct and isolated states, like an atom's ground and excited electronic states, that are involved in the emission of light, or, in the language of quantum computing, a qubit.        

"Superconducting quantum circuits allow one to perform fundamental quantum electrodynamics experiments using a microwave electrical circuit that looks like it could have been yanked directly from your cell phone," Painter says. "We believe that augmenting these circuits with superconducting metamaterials may enable future quantum computing technologies and further the study of more complex quantum systems that lie beyond our capability to model using even the most powerful classical computer simulations." 

The paper is titled "Superconducting metamaterials for waveguide quantum electrodynamics."

[Image: 1x1.gif] Explore further: A new way to count qubits

More information: Mohammad Mirhosseini et al. Superconducting metamaterials for waveguide quantum electrodynamics, Nature Communications (2018). DOI: 10.1038/s41467-018-06142-z


Journal reference: Nature Communications [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: California Institute of Technology


Read more at: https://phys.org/news/2018-09-supercondu...m.html#jCp






[Image: 1-quantummecha.jpg]
Quantum mechanics work lets oil industry know promise of recovery experiments before they start
With their current approach, energy companies can extract about 35 percent of the oil in each well. Every 1 percent above that, compounded across thousands of wells, can mean billions of dollars in additional revenue for ...
[Image: 1x1.gif]Sep 28, 2018 in Condensed Matter
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 obverse that effect  S33 Sheep  Y3S  affect this observe 

How does a quantum particle see the world?

January 30, 2019, University of Vienna


[Image: howdoesaquan.jpg]
Quantum features, such as quantum superposition, are only defined relative to an observer. When we look at the train from the point of view of an observer standing on the platform, the train looks in a quantum superposition of different positions. Credit: Christian Murzek/IQOQI-Vienna
Researchers at the University of Vienna study the relevance of quantum reference frames for the symmetries of the world




According to one of the most fundamental principles in physics, an observer on a moving train uses the same laws to describe a ball on the platform as an observer standing on the platform – physical lawsare independent on the choice of a reference frame. Reference frames such as the train and the platform are physical systems and ultimately follow quantum-mechanical rules. They can be, for example, in a quantum state of superposition of different positions at once. So, what would the description of the ball look like for an observer on such a "quantum platform"? Researchers at the University of Vienna and the Austrian Academy of Sciences proved that whether an object (in our example, the ball) shows quantum features depends on the reference frame. The physical laws, however, are still independent of it. The results are published in Nature Communications.



Physical systems are always described relative to a reference frame. For example, a ball bouncing on a railway platform can be observed either from the platform itself or from a passing train. A fundamental principle of physics, the principle of General Covariance, states that the laws of physics which describe the motion of the ball do not depend on the reference frame of the observer. This principle has been crucial in the description of motion since Galileo and central to the development of Einstein's theory of relativity. It entails information about symmetries of the laws of physics as seen from different reference frames.



[Image: 1-howdoesaquan.jpg]

However, an observer sitting on the train sees the observer on the platform and the ball in a quantum superposition. Credit: Christian Murzek/IQOQI-Vienna

Reference frames are physical systems, which ultimately follow quantum-mechanical rules. A group of researchers led by Časlav Brukner at the University of Vienna and the Institute for Quantum Optics and Quantum Information (IQOQI-Vienna) of the Austrian Academy of Sciences have asked themselves whether it is possible to formulate the laws of physics from the point of view of an observer "attached" to a quantum particle and to introduce a quantum reference frame. They were able to demonstrate that one can consider any quantum system as a quantum reference frame. In particular when an observer on the train sees the platform in a superposition of different positions at once, an observer on the platform sees the train in a superposition. As a consequence, it depends on the reference frame of the observer whether an object such as the ball exhibits quantum or classical properties.







The researchers showed that the Principle of Covariance is extended to such quantum reference frames. This means that the laws of physics retain their form independent of the choice of the quantum reference frame. "Our results suggest that the symmetries of the world have to be extended at a more fundamental level," says Flaminia Giacomini, the lead author of the paper. This insight might play a role at the interplay of quantum mechanics and gravity -a regime that is mostly still unexplored- as in that regime it is expected that the classical notion of reference frames will not be sufficient and that reference frames will have to be fundamentally quantum.



[Image: 1x1.gif] Explore further: How Einstein's equivalence principle extends to the quantum world



More information: Flaminia Giacomini et al. Quantum mechanics and the covariance of physical laws in quantum reference frames, Nature Communications (2019). DOI: 10.1038/s41467-018-08155-0 


Journal reference: Nature Communications [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: University of Vienna






obverse that effect CNOT GATES  Sheep S33 NOT STAT3S  affect this observe






Quote:Quantum doink-head

Two doink-head were used in this work. Both utilize 3 CNOT gates, which allow for the whole set of 3-qubit occupation numbers to be spanned with suitable single qubit rotations. 


Experimental data from a quantum computer verifies the generalized Pauli exclusion principle
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Communications Physicsvolume 2, Article number: 11 (2019) Download Citation[/size]

Abstract
“What are the consequences… that Fermi particles cannot get into the same state…” R. P. Feynman wrote of the Pauli exclusion principle, “In fact, almost all the peculiarities of the material world hinge on this wonderful fact.” In 1972 Borland and Dennis showed that there exist powerful constraints beyond the Pauli exclusion principle on the orbital occupations of Fermi particles, providing important restrictions on quantum correlation and entanglement. Here we use computations on quantum computers to experimentally verify the existence of these additional constraints. Quantum many-fermion states are randomly prepared on the quantum computer and tested for constraint violations. Measurements show no violation and confirm the generalized Pauli exclusion principle with an error of one part in one quintillion.

Introduction
While performing calculations with classical computers at IBM, Borland and Dennis discovered something unexpected and surprising about the electronic structure of atoms and molecules1. In 1926 Pauli had observed that no more than a single electron can occupy a given one-electron quantum state known as a spin orbital2. Formally, the Pauli exclusion principle implies that the spin-orbital occupations are rigorously bounded by zero and one. In their calculations Borland and Dennis discovered, however, that even in three-electron atoms and molecules there are additional constraints beyond the well-known exclusion principle. In 2006 Klyachko (and in 2008 with Altunbulak) presented a systematic mathematical procedure for generating these constraints for potentially arbitrary numbers of electrons and orbitals3,4. These inequalities, which have become known as generalized Pauli constraints5,6,7,8, provide new insights into the electronic structure of many-electron atoms and molecules7,9,10,11,12, the limitations of entanglement as a resource for quantum control13,14, as well as the fundamental distinctions between open and closed quantum systems15.
In this work we use quantum states prepared on a quantum computer to provide experimental verification of the generalized Pauli constraints. Quantum computers differ from classical computers in that quantum states can be prepared on the quantum computer. doink-head which utilize these quantum states promise a large computational advantage over known classical doink-head for solving critically important problems such as integer factorization, eigenvalues estimation, and fermionic simulation16,17,18,19. Rapid advances in quantum hardware and hybrid classical-quantum doink-head have led to multi-qubit experimental implementations20,21,22. We first randomly prepare the quantum state of a 3-electron system and second measure the occupations of the natural orbitals. The natural orbitals are the eigenfunctions of the 1-electron reduced density matrix (1-RDM) that is defined by integrating the many-electron density matrix over the coordinates of all electrons except one

1D(1;1¯)=Ψ(123)Ψ(1¯23)d2d31D(1;1¯)=∫Ψ(123)Ψ∗(1¯23)d2d3

(1)
in which Ψ(123) is the 3-electron wave function. The two-step process is repeated many times on the quantum computer to explore all possible physically realizable orbital occupations. Because of the generalized Pauli constraints a large convex set of orbital occupations should be experimentally forbidden. In contrast to the classical computations of Borland and Dennis, we are not representing the quantum states by matrices but rather preparing quantum states directly, which allows us to measure the orbital occupations experimentally.

Results
Measurement of 1-RDM eigenvalues
Pauli observed in 1926 that for quantum systems of fermion particles such as electrons the occupation ni of each spin orbital must obey the following inequalities:

0ni1,0≤ni≤1,

(2)
known as the Pauli exclusion principle or Pauli constraints. In 1963 Coleman proved mathematically that these constraints plus a normalization constraint in which the occupation numbers sum to Nare necessary and sufficient for the occupation numbers ni to represent at least one ensemble state of N electrons23. Borland and Dennis in 1972, however, discovered that there exist additional conditions on the occupation numbers for the representation of at least one pure state of N electrons, which are presently known as the generalized Pauli constraints1. A pure state is a quantum state that is describable by a single wave function. Borland and Dennis found the following generalized Pauli constraints for three electrons in six orbitals:

n5+n6n40n5+n6−n4≥0

(3)
where

n1+n6=1n1+n6=1

(4)

n2+n5=1n2+n5=1

(5)

n3+n4=1,n3+n4=1,

(6)
where ni are the natural-orbital occupations ordered from largest to smallest.
To test the generalized Pauli constraints on a quantum computer, we prepare an initial pure state |Ψ0(123)〉 of 3 fermions in 6 orbitals and perform arbitrary unitary transformations U^iU^i of the initial state to generate a set of random pure states |Ψi(123)〉 of 3 fermions in 6 orbitals

|Ψi(123)=U^i|Ψ0(123).|Ψi(123)⟩=U^i|Ψ0(123)⟩.

(7)
We measure the matrix elements of the 1-RDM of each state |Ψi(123)〉 generated on the quantum computer and check each 1-RDM to verify satisfaction of the generalized Pauli constraints for 3 fermions in 6 orbitals. The 1-RDM is diagonalized on a classical computer and the eigenvalues (natural occupation numbers) are inserted into the generalized Pauli constraints to check for satisfaction. The eigenvalues of the 1-RDM, ordered from highest to lowest, form a special type of convex set with “flat” sides known as a polytope. The boundaries or “flat” sides of the polytope are determined by the Pauli and generalized Pauli constraints. Suppose the experimental data satisfies the Pauli constraints but not the generalized Pauli constraints, then the smallest 3 eigenvalues of each measured 1-RDM will describe the Pauli polytope which is shown as the combined yellow and blue regions in Fig. 1. On the other hand, suppose the experimental data obeys not only the Pauli constraints but also the generalized Pauli constraints, then the smallest 3 eigenvalues of each measured 1-RDM will only describe the smaller generalized Pauli polytope, pictured as just the yellow region in Fig. 1. Comparison of the measured scatter plot of 1-RDM eigenvalues with these two polytopes provides an experimental means of observing the generalized Pauli constraints and thereby verifying their validity in a quantum system.
Fig. 1
[Image: 42005_2019_110_Fig1_HTML.png]
Orbital occupations of the 1-electron reduced density matrix (1-RDM) form convex polytopes. The eigenvalues (natural occupations) of the 1-RDM, ordered from largest to smallest, form a special convex set with “flat” sides known as a polytope. Because the three smallest eigenvalues for a 3-electrons-in-6-orbitals state (n4n5n6) determine the other eigenvalues, we can visualize the polytope in three dimensions. The figure shows two polytopes: (i) the Pauli polytope of eigenvalues obeying the ordinary Pauli constraints (the combination of the yellow and blue regions), as well as (ii) the generalized Pauli polytope of eigenvalues obeying the generalized Pauli constraints (the yellow region only). The plane separating the yellow and blue regions arises from the Borland-Dennis inequality shown in Eq. (3)

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The system of 3 fermions in 6 orbitals can be expressed as a system of 3 qubits, allowing the above procedure to be simplified. Because the occupations of each pair, {n1n6}, {n2n5}, and {n3n4}, must sum to one, the three electron system has a one-to-one mapping to a system of three qubits. The occupation numbers n4n5, and n6, which are eigenvalues of the 1-RDM, can be viewed as the eigenvalues p1p2, and p3 of the 1-qubit reduced density matrix of a 3-qubit system. Hence, for the 3-qubit system the generalized Pauli constraints in Eqs. (3)–(6) can be written as the single inequality

p2+p3p10,p2+p3−p1≥0,

(8)
which was first obtained by Higuchi in 200224. The Higuchi inequalities for N qubits are a subset of the generalized Pauli constraints for Nelectrons in 2N orbitals. In the case of three electrons in six orbitals the Higuchi inequality is equivalent to the generalized Pauli constraint in Eq. (3) under the assumption that Eqs. (46) hold. In the quantum computation we exploit this relationship to represent the 3 electron in 6 orbital quantum system efficiently as a 3 qubit system with a compact fermionic mapping, described in the Methods section. In this representation the violation of the Higuchi inequality in Eq. (8) is equivalent to the violation of the generalized Pauli inequality in Eq. (3).
The initial 3-qubit state is chosen to be the non-interacting state in which all 3 qubits are in their lower-energy (off) state. The arbitrary unitary transformations are generated on the quantum computer from

|Ψi(123)=C31Ry(γ)C13Ry(β)C21Ry(α)|Ψ0(123),|Ψi(123)⟩=C13Ry(γ)C31Ry(β)C12Ry(α)|Ψ0(123)⟩,

(9)
where the parameters αβ, and γ in the Pauli rotation matrices Ry(α) are chosen randomly and the CjiCij are controlled NOT (CNOT) gates. The rotation matrices are applied to the control qubit of the ensuing CNOT gate. It is known that any 3-qubit state can be prepared from the non-interacting state by a unitary transformation built from only 3 CNOT gates plus universal single-qubit gates25. The above transformation generates states that span the most general entanglement class for the system and whose 1-qubit RDMs cover all possible real 1-qubit occupation numbers14,26,27. Computations were also performed with a slightly more general transformation, discussed in the Methods and Supplementary Fig. 1, albeit without a significant change in the results. Because of the mapping between the 3-qubit and the 3-fermion-in-6-orbitals system, the measured occupations p1p2, and p3 are equivalent to the natural occupations (eigenvalues) n4n5, and n6 of the 1-RDM. For the remainder of this work we primarily discuss the results in terms of the 3-fermion system.
Verification of generalized Pauli constraints
The scatter plot of the measured 1-RDM natural occupations is shown in Fig. 2 relative to the Pauli polytope, the combination of the yellow and blue regions, and the smaller generalized Pauli polytope, only the yellow region. Results show that the physical system only accesses the generalized Pauli polytope (yellow), defined by the generalized Pauli constraints. None of the natural occupation numbers lie in the part (blue) of the Pauli polytope which is forbidden by the Borland-Dennis constraint. Therefore, the experimental data from the quantum computer verifies the generalization of the Pauli exclusion principle for pure states. Supplementary Fig. 2 visualizes the effect of error on the occupation numbers. We observe that the errors consistently push the triplet of occupations into the generalized Pauli polytope, which reflects upon the nature of the quantum noise. Despite the presence of quantum noise the fundamental result is statistically robust14. The Pauli polytope is twice the size of the generalized Pauli polytope. Consequently, without further restrictions beyond the ordinary Pauli constraints the probability of a randomly prepared state being in the yellow region would be one out of two. The probability of n random states being on the yellow side, therefore, would be 1/2n. With n being approximately 60, we observe that the probability of measuring all 60 points within the yellow region would be 1/260 or a highly improbable one in one quintillion. Hence, we have verified the generalized Pauli exclusion principle by quantum computer to a high degree of confidence.
Fig. 2
[Image: 42005_2019_110_Fig2_HTML.png]
Measured orbital occupations verify generalized Pauli principle. The scatter plot of the three lowest measured 1-electron reduced density matrix (1-RDM) eigenvalues (n4n5n6) is shown relative to the Pauli polytope, the combination of the yellow and blue regions, and the smaller generalized Pauli polytope, only the yellow region. Results show that none of the eigenvalues lie in the part (blue) of the Pauli polytope which is forbidden for pure quantum states by the Borland-Dennis constraint[/size]

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Despite the restrictions on the pure-state observables from the generalized Pauli constraints, the set of realizable 1-RDMs exhibits all limits of quantum behavior including the mean-field limit, as well as the strong-electron-correlation limit including phenomena like superconductivity. Figure 3 shows examples of chemical systems which widely vary in the degree of correlation present. As observed in previous work, for 3-electron-in-6-orbital systems the ground-state triplet of occupation numbers (n4n5n6) lies on the Borland-Dennis generalized Pauli constraint, separating pure and ensemble states in the set of 1-RDMs. Excited-state natural occupation numbers of these systems, in contrast, can lie on the generalized Pauli constraint like the ground states or elsewhere in the polytope, reflecting substantial variations in the one-electron properties of excited states7. The 3 lowest occupation numbers (n4n5n6) can be readily expressed in the natural-orbital basis set in terms of single, double, and triple excitations from the single determinant |ϕ1ϕ2ϕ3〉, composed of the 3 most occupied natural orbitals; for nu where u indicates the index of one of the unoccupied orbitals of the reference determinant we have

nu=i|cui|2+ija|cauij|2+ijkab|cabuijk|2nu=∑i⁡|ciu|2+∑ija⁡|cijau|2+∑ijkab⁡|cijkabu|2

(10)
in which ij, and k denote indices of natural orbitals in the reference determinant and a and b denote indices of natural orbitals not in the reference determinant and cuiciucauijcijaucabuijkcijkabu are the single-excitation, double-excitation, and triple-excitation coefficients. From the formula we observe that when (n4n5n6) equals (0, 0, 0), all of the excitation coefficients vanish, and the quantum state is the reference determinant 1ϕ2ϕ3〉. All other points in the polytope have contributions from one or more of the excitation coefficients. The triple excitations vanish when the natural occupation numbers (n4n5n6) are pinned to the Borland–Dennis inequality3,4,11. The triplet of occupation numbers from ground and excited states tends to gravitate towards the boundaries of the polytope, reflecting the interplay between the energy optimization and the restrictions imposed on fermions from the Pauli constraints.
Fig. 3
[Image: 42005_2019_110_Fig3_HTML.png]
Orbital occupations of correlated 3-electron atoms and molecules. The lowest three eigenvalues (natural occupations) of the 1-electron reduced density matrix (1-RDM) for ground and excited states of 3-electron-in-6-orbital atoms and molecules (n4n5n6) are shown: a Lithium atom (red) and the π orbitals of the Boron atom (blue). b Allyl radical in the cyclic form (C3H3, red) and linear H3 (blue). The triplet of occupation numbers from ground and excited states tends to gravitate towards the boundaries of the polytope, reflecting the interplay between the energy optimization and the restrictions imposed on fermions from the Pauli constraints. These eigenvalues were calculated by full configuration interaction on a classical computer[/size]

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https://www.nature.com/articles/s42005-019-0110-3
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#93
The force is with us, always? Tuning quantum vacuum forces from attractive to repulsive
March 4, 2019, Arizona State University

[Image: theforceiswi.jpg]
ASU physicist Frank Wilczek has shown for the first time that the Casimir force can be reversed and made repulsive, tunable or enhanced, depending on the properties of the material inserted in between the plates. Credit: Alan Stonebraker, American Physical Society
The force is strong not only in Star Wars lore but also as a fundamental property in physics. For example, scientists can put two uncharged metal plates close together in a vacuum, and "voila!" —-they will attract each other like Luke Skywalker and his trusted lightsaber.




In 1948, Dutch theoretical physicist Hendrick Casimir first predicted an attractive force responsible for this effect——later dubbed the Casimir effect. A half-century later, in 1996, the Casimir force was experimentally measured for the first time by Steve Lamoreaux at Los Alamos National Laboratory.

But just like the light and dark side of the force in Star Wars, scientists have wondered, can there be an equal yet opposite kind of Casimir force?

"Between two like materials, this force always corresponds to an attractive Casimir force, regardless of the mediating materials," said Arizona State University physicist Frank Wilczek. "Yet in principle the Casimir force can be repulsive."

Wilczek explains that generating a repulsive Casimir force has gained a great deal of interest in practical applications like the semiconductor industry, as chips have grown tinier and tinier with atomic-scale features.

"In recent years, people have devoted substantial efforts to realizing repulsive Casimir forces, especially with a view toward applications to nano-devices and colloids, which can contain nearby parts that one wants to keep separate."

Now, Wilczek, along with colleague Qing-Dong Jiang of Stockholm University, have shown for the first time that the Casimir force can be reversed and made repulsive, tunable or enhanced, depending on the properties of the material inserted in between the plates.

"We find that the Casimir force can, as a function of distance, oscillate between attractive and repulsive, and that it can be tuned by application of an external magnetic field," said

[Image: 1-theforceiswi.jpg]
To make the Casimir force between metal plates repulsive, Wilczek and Stockholm University colleague Qing-Dong Jiang inserted a material between the plates that breaks this behavior. This 'chiral' material (chiral comes from the Greek word …more
Wilczek, a professor of physics at ASU who also holds faculty appointments at Massachusetts Institute of Technology and Stockholm University.

Far from being a science about nothing, the "material" within the empty space of vacuums between the two metal plates, because of quantum effects, are actually rivers teeming with an invisible force—-electromagnetic waves that contain untapped energy. During the Casimir effect, as the plates are moved together, some of the waves in the vacuum are gradually squeezed out, giving more energy to their surroundings, and causing the attractive force.



The vacuum is filled with quantum fluctuations of the electromagnetic field—virtual photons that pop in and out of existence—-that are assumed to behave in the same way. To make the plates repulsive and tunable, Wilczek and Stockholm University colleague Qing-Dong Jiang inserted a material between the plates that breaks this behavior. This "chiral" material (chiral comes from the Greek word meaning hand) causes two types of photons that differ like your left and right hand, or in this case, right and left-circular polarized photons. The material causes the photons to have different velocities that can each transfer a different amount of momentum to the plates.

Wilczek and Jiang calculated the Casimir force between two plates for two types of intervening chiral materials and at different temperatures. They found that the force could be adjusted by changing the distance between the plates or changing the strength of an applied magnetic field. They found that making these adjustments could yield a repulsive Casimir force more than three times as strong as the attractive force for the same setup in a vacuum.

"The key to realizing repulsive Casimir forces between similar objects is to insert an intermediate chiral material between them," said Wilczek. "The chiral Casimir force has several distinctive features: it can be oscillatory, its magnitude can be large, and it can vary in response to external magnetic fields."

Their hope is that these results will provide physicists and engineers interested in semiconductors and nanodevices with a new way to explore the behaviors and properties of different materials at the quantum level.

"Through the connection of this force to independently measurable material properties, one obtains a wealth of predicted phenomena which directly reflect macroscopic effects of quantum fluctuations."

And perhaps, scientists can even draw a bit of innovational inspiration by tapping into their inner Star Wars geek from one of Darth Vader's most famous movie quotes:  Duel  "Don't underestimate the force."

Explore further: Raising the prospects for quantum levitation

More information: Qing-Dong Jiang et al, Chiral Casimir forces: Repulsive, enhanced, tunable, Physical Review B (2019). DOI: 10.1103/PhysRevB.99.125403 

Journal reference: Physical Review B
Provided by: Arizona State University



Read more at: https://phys.org/news/2019-03-tuning-quantum-vacuum-repulsive.html#jCp
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#94
More Than One Reality Exists (in Quantum Physics)
By Mindy Weisberger, Senior Writer March 20, 2019 07:00am ET

[img=553x0]https://img.purch.com/w/660/aHR0cDovL3d3dy5saXZlc2NpZW5jZS5jb20vaW1hZ2VzL2kvMDAwLzEwNC84MTgvb3JpZ2luYWwvZHVlbGluZy1yZWFsaXR5LXBob3RvbnM=[/img][Image: aHR0cDovL3d3dy5saXZlc2NpZW5jZS5jb20vaW1h...Bob3RvbnM=]

Different observations of the same reality (in photons) may both be correct, according quantum mechanics.
Credit: Shutterstock
Can two versions of reality exist at the same time? Physicists say they can — at the quantum level, that is.
Researchers recently conducted experiments to answer a decades-old theoretical physics question about dueling realities. This tricky thought experiment proposed that two individuals observing the same photon could arrive at different conclusions about that photon's state — and yet both of their observations would be correct.
For the first time, scientists have replicated conditions described in the thought experiment. Their results, published Feb. 13 in the preprint journal arXiv, confirmed that even when observers described different states in the same photon, the two conflicting realities could both be true. [The Biggest Unsolved Mysteries in Physics]

"You can verify both of them," study co-author Martin Ringbauer, a postdoctoral researcher with the Department of Experimental Physics at the University of Innsbrück in Austria, told Live Science.
Wigner's friend
This perplexing idea was the brainchild of Eugene Wigner, winner of the Nobel Prize for Physics in 1963. In 1961, Wigner had introduced a thought experiment that became known as "Wigner's friend." It begins with a photon — a particle of light. When an observer in an isolated laboratory measures the photon, they find that the particle's polarization — the axis on which it spins — is either vertical or horizontal.
However, before the photon is measured, the photon displays both polarizations at once, as dictated by the laws of quantum mechanics; it exists in a "superposition" of two possible states.
Once the person in the lab measures the photon, the particle assumes a fixed polarization. But for someone outside that closed laboratory who doesn't know the result of the measurements, the unmeasured photon is still in a state of superposition.
That outsider's observation — their reality — therefore diverges from the reality of the person in the lab who measured the photon. Yet, neither of those conflicting observations is thought to be wrong, according to quantum mechanics.
Altered states
For decades, Wigner's mind-bending proposal was just an interesting thought experiment. But in recent years, important advances in physicsfinally enabled experts to put Wigner's proposal to the test, Ringbauer said.
"Theoretical advances were needed to formulate the problem in a way that is testable. Then, the experimental side needed developments on the control of quantum systems to implement something like that," he explained.
Ringbauer and his colleagues tested Wigner's original idea with an even more rigorous experiment which doubled the scenario. They designated two "laboratories" where the experiments would take place and introduced two pairs of entangled photons, meaning that their fates were linked, so that knowing the state of one automatically tells you the state of the other. (The photons in the setup were real. Four "people" in the scenario — "Alice," "Bob" and a "friend" of each — were not real, but instead represented observers of the experiment).
The two friends of Alice and Bob, who were located "inside" each of the labs, each measured one photon in an entangled pair. This broke the entanglement and collapsed the superposition, meaning that the photon they measured existed in a definite state of polarization. They recorded the results in quantum memory — copied in the polarization of the second photon.
Alice and Bob, who were "outside" the closed laboratories, were then presented with two choices for conducting their own observations. They could measure their friends' results that were stored in quantum memory, and thereby arrive at the same conclusions about the polarized photons.
But they could also conduct their own experiment between the entangled photons. In this experiment, known as an interference experiment, if the photons act as waves and still exist in a superposition of states, then Alice and Bob would see a characteristic pattern of light and dark fringes, where the peaks and valleys of the light waves add up or cancel each other out. If the particles have "chosen" their state, you'd see a different pattern than if they hadn't. Wigner had previously proposed that this would reveal that the photons were still in an entangled state.
The authors of the new study found that even in their doubled scenario, the results described by Wigner held. Alice and Bob could arrive at conclusions about the photons that were correct and provable and that yet still differed from the observations of their friends — which were also correct and provable, according to the study.
Quantum mechanics describes how the world works at a scale so small that the normal rules of physics no longer apply; over many decades, experts who study the field have offered numerous interpretations of what that means, Ringbauer said.
However, if measurements themselves aren't absolutes — as these new findings suggest — that challenges the very meaning of quantum mechanics.
"It seems that, in contrast to classical physics, measurement results cannot be considered absolute truth but must be understood relative to the observer who performed the measurement," Ringbauer said.
"The stories we tell about quantum mechanics have to adapt to that," he said.

Originally published on Live Science.


https://www.livescience.com/65029-duelin...otons.html





Physicists reverse time using quantum computer

March 13, 2019, Moscow Institute of Physics and Technology



[Image: physicistsre.jpg]
Credit: @tsarcyanide/MIPT
Researchers from the Moscow Institute of Physics and Technology teamed up with colleagues from the U.S. and Switzerland and returned the state of a quantum computer a fraction of a second into the past. They also calculated the probability that an electron in empty interstellar space will spontaneously travel back into its recent past. The study is published in Scientific Reports.








"This is one in a series of papers on the possibility of violating the second law of thermodynamics. That law is closely related to the notion of the arrow of time that posits the one-way direction of time from the past to the future," said the study's lead author Gordey Lesovik, who heads the Laboratory of the Physics of Quantum Information Technology at MIPT.



"We began by describing a so-called local perpetual motion machine of the second kind. Then, in December, we published a paper that discusses the violation of the second law via a device called a Maxwell's demon," Lesovik said. "The most recent paper approaches the same problem from a third angle: We have artificially created a state that evolves in a direction opposite to that of the thermodynamic arrow of time."



What makes the future different from the past



Most laws of physics make no distinction between the future and the past. For example, let an equation describe the collision and rebound of two identical billiard balls. If a close-up of that event is recorded with a camera and played in reverse, it can still be represented by the same equation. Moreover, it is not possible to distinguish from the recording if it has been doctored. Both versions look plausible. It would appear that the billiard balls defy the intuitive sense of time.



However, imagine recording a cue ball breaking the pyramid, the billiard balls scattering in all directions. In that case, it is easy to distinguish the real-life scenario from reverse playback. What makes the latter look so absurd is our intuitive understanding of the second law of thermodynamics—an isolated system either remains static or evolves toward a state of chaos rather than order.



Most other laws of physics do not prevent rolling billiard balls from assembling into a pyramid, infused tea from flowing back into the tea bag, or a volcano from "erupting" in reverse. But these phenomena are not observed, because they would require an isolated system to assume a more ordered state without any outside intervention, which runs contrary to the second law. The nature of that law has not been explained in full detail, but researchers have made great headway in understanding the basic principles behind it.







Spontaneous time reversal



Quantum physicists from MIPT decided to check if time could spontaneously reverse itself at least for an individual particle and for a tiny fraction of a second. That is, instead of colliding billiard balls, they examined a solitary electron in empty interstellar space.



"Suppose the electron is localized when we begin observing it. This means that we're pretty sure about its position in space. The laws of quantum mechanics prevent us from knowing it with absolute precision, but we can outline a small region where the electron is localized," says study co-author Andrey Lebedev from MIPT and ETH Zurich.



The physicist explains that the evolution of the electron state is governed by Schrödinger's equation. Although it makes no distinction between the future and the past, the region of space containing the electron will spread out very quickly. That is, the system tends to become more chaotic. The uncertainty of the electron's position is growing. This is analogous to the increasing disorder in a large-scale system—such as a billiard table—due to the second law of thermodynamics.







[Image: 1-physicistsre.jpg]

The four stages of the actual experiment on a quantum computer mirror the stages of the thought experiment involving an electron in space and the imaginary analogy with billiard balls. Each of the three systems initially evolves from order …more"However, Schrödinger's equation is reversible," adds Valerii Vinokur, a co-author of the paper, from the Argonne National Laboratory, U.S. "Mathematically, it means that under a certain transformation called complex conjugation, the equation will describe a 'smeared' electron localizing back into a small region of space over the same time period." Although this phenomenon is not observed in nature, it could theoretically happen due to a random fluctuation in the cosmic microwave background permeating the universe.





The team set out to calculate the probability to observe an electron "smeared out" over a fraction of a second spontaneously localizing into its recent past. It turned out that even across the entire lifetime of the universe—13.7 billion years—observing 10 billion freshly localized electrons every second, the reverse evolution of the particle's state would only happen once. And even then, the electron would travel no more than a mere one ten-billionth of a second into the past.



Large-scale phenomena involving billiard balls and volcanoes obviously unfold on much greater timescales and feature an astounding number of electrons and other particles. This explains why we do not observe old people growing younger or an ink blot separating from the paper.



Reversing time on demand



The researchers then attempted to reverse time in a four-stage experiment. Instead of an electron, they observed the state of a quantum computer made of two and later three basic elements called superconducting qubits.


  • Stage 1: Order. Each qubit is initialized in the ground state, denoted as zero. This highly ordered configuration corresponds to an electron localized in a small region, or a rack of billiard balls before the break.

  • Stage 2: Degradation. The order is lost. Just like the electron is smeared out over an increasingly large region of space, or the rack is broken on the pool table, the state of the qubits becomes an ever more complex changing pattern of zeros and ones. This is achieved by briefly launching the evolution program on the quantum computer. Actually, a similar degradation would occur by itself due to interactions with the environment. However, the controlled program of autonomous evolution will enable the last stage of the experiment.

  • Stage 3: Time reversal. A special program modifies the state of the quantum computer in such a way that it would then evolve "backwards," from chaos toward order. This operation is akin to the random microwave background fluctuation in the case of the electron, but this time, it is deliberately induced. An obviously far-fetched analogy for the billiards example would be someone giving the table a perfectly calculated kick.

  • Stage 4: Regeneration. The evolution program from the second stage is launched again. Provided that the "kick" has been delivered successfully, the program does not result in more chaos but rather rewinds the state of the qubits back into the past, the way a smeared electron would be localized or the billiard balls would retrace their trajectories in reverse playback, eventually forming a triangle.


The researchers found that in 85 percent of the cases, the two-qubit quantum computer returned back into the initial state. When three qubits were involved, more errors happened, resulting in a roughly 50 percent success rate. According to the authors, these errors are due to imperfections in the actual quantum computer. As more sophisticated devices are designed, the error rate is expected to drop.



Interestingly, the time reversal doink-headitself could prove useful for making quantum computers more precise. "Our doink-headcould be updated and used to test programs written for quantum computers and eliminate noise and errors," Lebedev explained.



[Image: 1x1.gif] Explore further: Quantum Maxwell's demon 'teleports' entropy out of a qubit



More information: G. B. Lesovik et al. Arrow of time and its reversal on the IBM quantum computer, Scientific Reports (2019). DOI: 10.1038/s41598-019-40765-6 



Journal reference: Scientific Reports [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: Moscow Institute of Physics and Technology





Read more at: https://phys.org/news/2019-03-physicists-reverse-quantum.html#jCp
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#95
Optic Topic



Researchers measure quantum behavior at room temperature, visible to the naked eye
March 25, 2019 by Elsa Hahne, Louisiana State University

[Image: listeningtot.jpg]
Louisiana State University Department of Physics & Astronomy Associate Professor Thomas Corbitt and his team of researchers now present the first broadband, off-resonance measurement of quantum radiation pressure noise in the audio band, at …more


Since the historic finding of gravitational waves from two black holes colliding over a billion light years away was made in 2015, physicists are advancing knowledge about the limits on the precision of the measurements that will help improve the next generation of tools and technology used by gravitational wave scientists.




Louisiana State University Department of Physics & Astronomy Associate Professor Thomas Corbitt and his team of researchers now present the first broadband, off-resonance measurement of quantum radiation pressure noise in the audio band, at frequencies relevant to gravitational wave detectors, as reported today in the scientific journal Nature.

The research was supported by the National Science Foundation, or NSF, and the results hint at methods to improve the sensitivity of gravitational-wave detectors by developing techniques to mitigate the imprecision in measurements called "back action," thus increasing the chances of detecting gravitational waves.

Corbitt and researchers have developed physical devices that make it possible to observe—and hear—quantum effects at room temperature. It is often easier to measure quantum effects at very cold temperatures, while this approach brings them closer to human experience. Housed in miniature models of detectors like LIGO, or the Laser Interferometer Gravitational-Wave Observatory, located in Livingston, La., and Hanford, Wash., these devices consist of low-loss, single-crystal micro-resonators—each a tiny mirror pad the size of a pin prick, suspended from a cantilever. A laser beam is directed at one of these mirrors, and as the beam is reflected, the fluctuating radiation pressure is enough to bend the cantilever structure, causing the mirror pad to vibrate, which creates noise.

[Image: 1-listeningtot.jpg]
Louisiana State University Department of Physics & Astronomy Associate Professor Thomas Corbitt and his team of researchers now present the first broadband, off-resonance measurement of quantum radiation pressure noise in the audio band, at …more
Gravitational wave interferometers use as much laser power as possible in order to minimize the uncertainty caused by the measurement of discrete photons and to maximize the signal-to-noise ratio. These higher power beams increase position accuracy but also increase back action, which is the uncertainty in the number of photons reflecting from a mirror that corresponds to a fluctuating force due to radiation pressure on the mirror, causing mechanical motion. Other types of noise, such as thermal noise, usually dominate over quantum radiation pressure noise, but Corbitt and his team, including collaborators at MIT, have sorted through them. Advanced LIGO and other second and third generation interferometers will be limited by quantum radiation pressure noise at low frequencies when running at their full laser power. Corbitt's paper in Nature offers clues as to how researchers can work around this when measuring gravitational waves.



"Given the imperative for more sensitive gravitational wave detectors, it is important to study the effects of quantum radiation pressure noise in a system similar to Advanced LIGO, which will be limited by quantum radiation pressure noise across a wide range of frequencies far from the mechanical resonance frequency of the test mass suspension," Corbitt said.

Corbitt's former academic advisee and lead author of the Nature paper, Jonathan Cripe, graduated from LSU with a Ph.D. in physics last year and is now a postdoctoral research fellow at the National Institute of Standards and Technology:



[Image: 2-listeningtot.jpg]
Louisiana State University Department of Physics & Astronomy Associate Professor Thomas Corbitt and his team of researchers now present the first broadband, off-resonance measurement of quantum radiation pressure noise in the audio band, at …more"Day-to-day at LSU, as I was doing the background work of designing this experiment and the micro-mirrors and placing all of the optics on the table, I didn't really think about the impact of the future results," Cripe said. "I just focused on each individual step and took things one day at a time. [But] now that we have completed the experiment, it really is amazing to step back and think about the fact that quantum mechanics—something that seems otherworldly and removed from the daily human experience—is the main driver of the motion of a mirror that is visible to the human eye. The quantum vacuum, or 'nothingness,' can have an effect on something you can see."


Pedro Marronetti, a physicist and NSF program director, notes that it can be tricky to test new ideas for improving gravitational wave detectors, especially when reducing noise that can only be measured in a full-scale interferometer:

"This breakthrough opens new opportunities for testing noise reduction," he said. The relative simplicity of the approach makes it accessible by a wide range of research groups, potentially increasing participation from the broader scientific community in gravitational wave astrophysics."

[Image: 1x1.gif] Explore further: Innovation increases observable volume of the universe by a factor of seven

More information: Jonathan Cripe et al, Measurement of quantum back action in the audio band at room temperature, Nature (2019). DOI: 10.1038/s41586-019-1051-4 

Journal reference: Nature [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: Louisiana State University



Read more at: https://phys.org/news/2019-03-quantum-be...e.html#jCp
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