Amazing Science
779.4K views | +26 today
Follow
Amazing Science
Amazing science facts - 3D_printing • aging • AI • anthropology • art • astronomy • bigdata • bioinformatics • biology • biotech • chemistry • computers • cosmology • education • environment • evolution • future • genetics • genomics • geosciences • green_energy • history • language • map • material_science • math • med • medicine • microscopy • nanotech • neuroscience • paleontology • photography • photonics • physics • postings • robotics • science • technology • video
Your new post is loading...
Scooped by Dr. Stefan Gruenwald
Scoop.it!

How to make electrons behave like a liquid

How to make electrons behave like a liquid | Amazing Science | Scoop.it
Physicists have found that electrons can sometimes show collective behavior to produce vortices and backward flow of electric current known as “negative resistance.”


Electrical resistance is a simple concept: Rather like friction slowing down an object rolling on a surface, resistance slows the flow of electrons through a conductive material. But two physicists have now found that electrons can sometimes cooperate to turn resistance on its head, producing vortices and backward flow of electric current.


The prediction of “negative resistance” is just one of a set of counterintuitive and bizarre fluid-like effects encountered under certain exotic circumstances, involving systems of strongly interacting particles in a sheet of graphene, a two-dimensional form of carbon. The findings are described in a paper appearing today in the journal Nature Physics, by MIT professor of physics Leonid Levitov and Gregory Falkovich, a professor at Israel’s Weizmann Institute of Science.


Electrons in graphene move in a neatly coordinated way, in many ways resembling the movement of viscous fluids through a tube where they are strongly affected by turbulence and vortices. This is due to interactions producing a long-range current-field response, quite different from the simple “individualist” behavior expected under ordinary circumstances, when electrons move in straight lines like pinballs bouncing among the ions, as described by Ohm's law, the researchers say.


The notion of electron viscosity had been suggested before in theory, but it had proven difficult to test because nobody had come up with a way to directly observe such phenomena. Now, Levitov and Falkovich say they have figured out a set of signs that can serve as an indicator of such collective effects in electron flows.


This work is “a remarkable application of theoretical insight to the prediction of a new experimentally observable effect,” says Subir Sachdev, a professor of physics at Harvard University who was not involved in this work. He says this insight is “very significant and opens a new chapter in the study of electron flow in metals.”

more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

Physicists Test the Response Time of Electrons

Physicists Test the Response Time of Electrons | Amazing Science | Scoop.it

Researchers from the Laboratory for Attosecond Physics generated for the first time visible flashes of light in attosecond dimensions. They dispatched the light-flashes to electrons in krypton atoms. Through the experiment the researchers have been able to display that the electrons, which are stimulated by the flashes, needed roughly 100 attoseconds to respond to the incident light. Until now it was assumed that particles respond to incident light without delay.


Light could be the driving force which makes electronics even faster in the future. This is how physicists pursue their goal of using short pulses of light to control electric currents in circuits at the same rate as the frequency of light. The attophysics discovery made by an international team working with Eleftherios Goulielmakis, Leader of the Attoelectronics Research Group at the Max Planck Institute of Quantum Optics, may make it possible in future to use light to control electrons much more precisely than ever before. This is because electrons apparently follow the electromagnetic forces of light with a slight delay. The researchers determined the time it takes the electrons to react to light by exciting electrons in krypton atoms with attosecond pulses of visible light. They observed that it takes around 100 attoseconds (one attosecond is a billionth of a billionth of a second) until the particles’ reaction to the light pulses becomes noticeable. Physicists previously had to assume that the force of light has an immediate effect because they were unable to measure the delay.


An electron weighs almost nothing at all. If you want to express its mass in grams, you have to write 27 zeros after the decimal point before you can write the first number. But even this lightweight is sluggish, a little bit at least. Quantum mechanics predicts that an electron also needs a certain, albeit very short, period of time to react to the forces of light. Since this takes only several tens to hundreds of attoseconds, this process was considered to be unmeasurably fast – until now. Researchers from the Max Planck Institute of Quantum Optics working with colleagues at Texas A&M University (USA) and Lomonosov Moscow State University (Russia) are now the first to have stopped this reaction time, as it were.


“Our research thereby puts an end to the decade-long debate about the fundamental dynamics of the light-matter interaction,” says Eleftherios Goulielmakis. In recent decades, researchers were already in a position to track both the rotations as well as the nuclear motions in molecules. “This is the first time that we are able to also track the reaction of the electrons bound in the atoms in real time,” stresses Goulielmakis. “But at the same time we are now standing on the threshold of a new era in which we will investigate and manipulate matter by influencing electrons.”


In the current publication, the researchers namely present not only the first measurements of how long an electron takes to respond to a light pulse. They also present the means that made this measurement possible in the first place, and which will enable completely new experiments with electrons to be carried out in the future: a way of tailoring pulses of visible light.

more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

Material deformation at atomic scale resembles avalanches

Material deformation at atomic scale resembles avalanches | Amazing Science | Scoop.it

The rearrangement of particles in materials during deformation, such as when a spoon is bent, doesn't occur independently, but rather resembles highly collective avalanches that span the entire material. This is the conclusion of experimental research conducted by researchers from the University of Amsterdam (UvA) and the University of Illinois at Urbana-Champaign. The team's findings, which are published in the latest edition of Nature Communications, offers a new universal theory of deformation.


Within the field of physics, the every-day deformation of materials has traditionally been described in very different contexts. For example, when a spoon is bent or a mobile phone cover shaped during production, small sporadic atomic rearrangements occur that ultimately give rise to the changing shape of the material. In soft materials such as cream or tooth paste, similar rearrangements occur with much larger constituent particles giving rise to the overall shape change. However, until now attempts to describe what exactly happens during the deformation process have been impeded by the large length-scale gap between microscopic rearrangements and macroscopic deformation. This has precluded a complete understanding of deformation processes.


'Avalanches are important phenomena that occur not only in the surge of snow down an incline, but also in a wider context such as through the spread of forest fires, diseases or in the dynamics of stock markets', says Peter Schall, professor of Soft Condensed Matter Physics at the UvA and one of the researchers who took part in the project. 'They typically develop in highly collective systems that are distinct by their critical state and in which a small event can trigger a large effect.'


The beauty of this finding is that deformation – like many other avalanche phenomena – are described by identical statistical distributions, thereby allowing unification of widely different phenomena, says Schall. 'For the process of deformation, this offers a new universal theory in which the gap between microscopic rearrangements and macroscopic flow is bridged by simple, self-similar scaling relations. These are independent of the material and can include anything from nanorods to rocks to everyday materials. This greatly reduces the complexity of the phenomenon into a unifying framework and should ultimately lead to the better prediction and design of material properties.

more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

Einstein’s Gravitational Waves Detected Originating from Merging Black Holes 1.3 Billion Years Ago

Einstein’s Gravitational Waves Detected Originating from Merging Black Holes 1.3 Billion Years Ago | Amazing Science | Scoop.it
Today, scientists announced that, for the first time in history, gravitational waves have been detected.

Gravitational waves are ripples in spacetime throughout the universe. What’s truly remarkable about this discovery is that Albert Einstein predicted the existence of gravitational waves 100 years ago, but scientists have never been able to detect them, until now.

The discovery came out of the U.S. based Laser Interferometer Gravitational Wave Observatory (LIGO). The mission of LIGO was to directly measure gravitational waves. In order to do that, LIGO scientists needed to construct the most precise measuring device the world had ever seen.

The LIGO project, which began in 1992, was the largest scientific investment the National Science Foundation (NSF) has ever made.

At an NSF press conference this morning, LIGO Laboratory Executive Director, David Reitze, said “This was a scientific moon shot. And we did it – we landed on the moon.”


LIGO consists of two 4 kilometer (2.5 mile) tunnels located in Louisiana and the state of Washington. Because gravitational waves stretch space in one direction and compress space in the other, LIGO was designed to measure changes in length across large land distances. If they could detect a stretch of land in the LIGO tunnels in one direction and compression in the other, they could theoretically detect a gravitational wave.


The “ruler” that scientists used to measure these tunnel lengths was the speed of light. The speed of light is constant, so LIGO can determine the length of the tunnels by measuring the time it takes for a laser to bounce from one end of the tunnel to the other.


Gravitational waves are created when masses accelerate. Measured back on September 14th, 2015, the gravitational wave signal that the LIGO scientists detected matches the exact signal they’d expect from two merging black holes accelerating at half the speed of light.


Reitze explained that the black holes that created this gravitational wave merged 1.3 billion years ago. It took that long for the wave to travel to the Earth. Each of the black holes were 30 times the mass of the sun and were accelerating at half the speed of light when they collided into each other. The ability to measure gravitational waves will open up an entirely new window for astronomy. Reitze explained that this will enable scientists to look at the universe in a new way.


more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

Physicists investigate the structure of time, with implications for quantum mechanics and philosophy

Physicists investigate the structure of time, with implications for quantum mechanics and philosophy | Amazing Science | Scoop.it

Although in theory it may seem possible to divide time up into infinitely tiny intervals, the smallest physically meaningful interval of time is widely considered to be the Planck time, which is approximately 10-43 seconds. This ultimate limit means that it is not possible for two events to be separated by a time smaller than this.


But now in a new paper, physicists have proposed that the shortest physically meaningful length of time may actually be several orders of magnitude longer than the Planck time. In addition, the physicists have demonstrated that the existence of such a minimum time alters the basic equations of quantum mechanics, and as quantum mechanics describes all physical systems at a very small scale, this would change the description of all quantum mechanical systems.


The researchers, Mir Faizal at the University of Waterloo and University of Lethbridge in Canada, Mohammed M. Khalil at Alexandria University in Egypt, and Saurya Das at the University of Lethbridge, have recently published a paper called "Time crystals from minimum time uncertainty" in The European Physical Journal C.


"It might be possible that, in the universe, the minimum time scale is actually much larger than the Planck time, and this can be directly tested experimentally," Faizal explainsThe Planck time is so short that no experiment has ever come close to examining it directly—the most precise tests can access a time interval down to about 10−17 seconds.


Nevertheless, there is a great deal of theoretical support for the existence of the Planck time from various approaches to quantum gravity, such as string theory, loop quantum gravity, and perturbative quantum gravity. Almost all of these approaches suggest that it is not possible to measure a length shorter than the Planck length, and by extension not possible to measure a time shorter than the Planck time, since the Planck time is defined as the time it takes light to travel a single unit of the Planck length in a vacuum.


Motivated by several recent theoretical studies, the scientists further delved into the question of the structure of time—in particular, the long-debated question of whether time is continuous or discrete. "In our paper, we have proposed that time is discrete in nature, and we have also suggested ways to experimentally test this proposal," Faizal said.


One possible test involves measuring the rate of spontaneous emission of a hydrogen atom. The modified quantum mechanical equation predicts a slightly different rate of spontaneous emission than that predicted by the unmodified equation, within a range of uncertainty. The proposed effects may also be observable in the decay rates of particles and of unstable nuclei.


Based on their theoretical analysis of the spontaneous emission of hydrogen, the researchers estimate that the minimum time may be orders of magnitude larger than the Planck time, but no greater than a certain amount, which is fixed by previous experiments. Future experiments could lower this bound on the minimum time or determine its exact value.


The scientists also suggest that the proposed changes to the basic equations of quantum mechanics would modify the very definition of time. They explain that the structure of time can be thought of as a crystal structure, consisting of discrete, regularly repeating segments.


On a more philosophical level, the argument that time is discrete suggests that our perception of time as something that is continuously flowing is just an illusion.

more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

Solving hard quantum problems: Everything is connected

Solving hard quantum problems: Everything is connected | Amazing Science | Scoop.it
Quantum physics is a game of luck and randomness. Initially, the atoms in a cold atom cloud do not have a predetermined position. Much like a die whirling through the air, where the number is yet to be determined, the atoms are located at all possible positions at the same time. Only when they are measured, their positions are fixed. "We shine light on the atom cloud, which is then absorbed by the atoms", says Kaspar Sakmann. "The atoms are photographed, and this is what determines their position. The result is completely random."

There is, however, an important difference between quantum randomness and a game of dice: if different dice are thrown at the same time, they can be seen as independent from each other. Whether or not we roll a six with die number one does not influence the result of die number seven. The atoms in the atom cloud on the other hand are quantum physically connected. It does not make sense to analyse them individually, they are one big quantum object. Therefore, the result of every position measurement of any atom depends on the positions of all the other atoms in a mathematically complicated way.

"It is not hard to determine the probability that a particle will be found at a specific position", says Kaspar Sakmann. "The probability is highest in the centre of the cloud and gradually diminishes towards the outer fringes." In a classically random system, this would be all the information that is needed. If we know that in a dice roll, any number has the probability of one sixth, then we can also determine the probability of rolling three ones with three dice. Even if we roll five ones consecutively, the probability remains the same the next time. With quantum particles, it is more complicated than that.

"We solve this problem step by step", says Sakmann. "First we calculate the probability of the first particle being measured on a certain position. The probability distribution of the second particle depends on where the first particle has been found. The position of the third particle depends on the first two, and so on." In order to be able to describe the position of the very last particle, all the other positions have to be known. This kind of quantum entanglement makes the problem mathematically extremely challenging.


But these correlations between many particles are extremely important - for example for calculating the behaviour of colliding Bose-Einstein-condensates. "The experiment shows that such collisions can lead to a special kind of quantum waves. On certain positions we find many particles, on an adjacent position we do not find any", says Kaspar Sakmann. "If we consider the atoms separately, this cannot be explained. Only if we take the full quantum distribution into account, with all its higher correlations, these waves can be reproduced by our calculations."


Also other phenomena have been calculated with the same method, for instance Bose-Einstein-condensates which are stirred with a laser beam, so that little vortices emerge - another typical quantum many-particle-effect. "Our results show how important theses correlations are and that it is possible to include them in quantum calculations, in spite of all mathematical difficulties", says Sakmann. With certain modifications, the approach can be expected to be useful for many other quantum systems as well.

more...
No comment yet.
Rescooped by Dr. Stefan Gruenwald from Fragments of Science
Scoop.it!

Seeing where energy goes may bring scientists closer to realizing nuclear fusion

Seeing where energy goes may bring scientists closer to realizing nuclear fusion | Amazing Science | Scoop.it

An international team of researchers has taken a step toward achieving controlled nuclear fusion--a process that powers the Sun and other stars, and has the potential to supply the world with limitless, clean energy. The team, led by scientists and engineers at the University of California, San Diego and General Atomics, developed a new technique to "see" where energy is delivered during a process called fast ignition, which is an approach to initiate nuclear fusion reactions using a high-intensity laser. Visualizing the energy flow enabled researchers to test different ways to improve energy delivery to the fuel target in their experiments. The researchers published their findings online in the Jan. 11 issue of the journal Nature Physics.


Fast ignition involves two stages to start nuclear fusion. First, hundreds of lasers compress the fusion fuel (typically a mix of deuterium and tritium contained in a spherical plastic fuel capsule) to high density. Then, a high-intensity laser delivers energy to rapidly heat (ignite) the compressed fuel. Scientists consider fast ignition a promising approach toward controlled nuclear fusion because it requires less energy than other approaches.


But in order for fast ignition to succeed, scientists need to overcome a big hurdle: how to direct energy from the high-intensity laser into the densest region of the fuel. "This has been a major research challenge since the idea of fast ignition was proposed," said Farhat Beg, professor of mechanical and aerospace engineering and director of the Center for Energy Research at UC San Diego.


To tackle this problem, the team devised a way to see, for the first time, where energy travels when the high-intensity laser hits the fuel target. The technique relies on the use of copper tracers inside the fuel capsule. When the high-intensity laser beam is directed at the compressed fuel target, it generates high-energy electrons that hit the copper tracers and cause them to emit X-rays that scientists can image.


"Before we developed this technique, it was as if we were looking in the dark. Now, we can better understand where energy is being deposited so we can investigate new experimental designs to improve delivery of energy to the fuel," said Christopher McGuffey, assistant project scientist in Beg's High Energy Density Physics Group at the UC San Diego Jacobs School of Engineering and co-author on the paper.


And that's what the team did. After experimenting with different fuel target designs and laser configurations, researchers eventually achieved a record high (up to 7 percent) efficiency of energy delivery from the high-intensity laser to the fuel. This result demonstrates an improvement on efficiency by about a factor of four compared to previous fast ignition experiments, researchers said.


Computer simulations also predicted an energy delivery efficiency as high as 15 percent if the experimental design was scaled up. But this prediction still needs to be tested experimentally, said Beg. "We hope this work opens the door to future attempts to improve fast ignition."


Via Mariaschnee
more...
No comment yet.
Rescooped by Dr. Stefan Gruenwald from Systems Theory
Scoop.it!

Mysterious LHC Photons Have Physicists Searching for Answers

Mysterious LHC Photons Have Physicists Searching for Answers | Amazing Science | Scoop.it
Physicists working at the Large Hadron Collider reported an unusual bump in their signal. But this time, they have no idea where the bump came from.


THREE WEEKS AGO, upon sifting through the aftermath of their proton-smashing experiments, physicists working at the Large Hadron Collider reported an unusual bump in their signal: the signature of two photons simultaneously hitting a detector. Physicists identify particles by reading these signatures, which result from the decay of larger, unstable particles that form during high-energy collisions. It’s how they discovered the Higgs boson back in 2012. But this time, they had no idea where the photons came from.


If—and at this point, it’s a big, fat if—this bump is real and not a statistical anomaly, it is a game-changer for physicists’ understanding of the universe. The signature can’t be explained by the Standard Model, the current rulebook for how all particles behave and interact. That could mean entirely new physics—though what kind, researchers don’t yet know.


“We were like, ‘Whoa, what is that?’” says Adam Martin, a physicist at the University of Notre Dame who recently submitted a paper theorizing about the bump to arXiv, the online, pre-peer review science repository. “What if it’s a new particle? What if it’s two?”


The physicists’ excitement comes with a heavy dose of pragmatism. No one is claiming that the bump is a new particle yet because the data simply isn’t good enough. “I can’t tell you if this bump is going to break the books or just fade away,” says Don Lincoln, a physicist at Fermilab who works with CMS, a group that detected the bump. Their measurement had a one in 10 chance of being a statistical fluke.


Those odds are no cause for fanfare, but CMS isn’t the only team that measured the bump; another, Atlas, saw it too. Atlas’s measurement had a one in 100 chance of being an anomaly—also not great, considering that the gold standard for a particle physics discovery is one in 3.5 million. But taken together, the two results were enough to get the field excited.


Via Ben van Lier
more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

Study reveals shared behavior of microbes and electrons

Study reveals shared behavior of microbes and electrons | Amazing Science | Scoop.it

There are certain universal patterns in nature that hold true, regardless of objects' size, species, or surroundings. Take, for instance, the branching fractals seen in both tree limbs and blood vessels, or the surprisingly similar spirals in mollusks and cabbage.


Now scientists at MIT and Cambridge University have identified an unexpected shared pattern in the collective movement of bacteria and electrons: As billions of bacteria stream through a microfluidic lattice, they synchronize and swim in patterns similar to those of electrons orbiting around atomic nuclei in a magnetic material.


The researchers found that by tuning certain dimensions of the microfluidic lattice, they were able to direct billions of microbes to align and swim in the same direction, much the way electrons circulate in the same direction when they create a magnetic field. With slight changes to the lattice, groups of bacteria flowed in opposite directions, resembling electrons in a nonmagnetic material.


Surprisingly, the researchers also identified a mathematical model that applies to the motions of both bacteria and electrons. The model derives from a general lattice field theory, which is typically used to describe the quantum behavior of electrons in magnetic and electronic materials. The researchers reduced this complex model to a much simpler, "textbook" model, which predicts that a phase transition, or a change in flow direction, should occur with certain changes to a lattice's dimensions -- a transition that the team observed in their experiments with bacteria.


"It's very surprising that we see this universality," says Jörn Dunkel, assistant professor of applied mathematics at MIT. "The really nice thing is, you have a living system here that shows all these behaviors that people think are also going on in quantum systems."


Dunkel and his colleagues at Cambridge University -- Hugo Wioland, Francis Woodhouse, and Raymond Goldstein '83 -- published their results yesterday in the journal Nature Physics.

more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

Understanding the mechanism for generating electric current without energy consumption at room temperature

Understanding the mechanism for generating electric current without energy consumption at room temperature | Amazing Science | Scoop.it

A group of researchers in Japan and China identified the requirements for the development of new types of extremely low power consumption electric devices by studying Cr-doped (Sb, Bi)2Te3 thin films. This study has been reported in Nature Communications.


At extremely low temperatures, an electric current flows around the edge of the film without energy loss, and under no external magnetic field. This attractive phenomenon is due to the material's ferromagnetic properties; however, so far, it has been unclear how the material gains this property. For the first time, researchers have revealed the mechanism by which this occurs. “Hopefully, this achievement will lead to the creation of novel materials that operate at room temperature in the future,” said Akio Kimura, a professor at Hiroshima University and a member of the research group.


Their achievement can be traced back to the discovery of the quantum Hall effect in the 1980’s, where an electric current flows along an edge (or interface) without energy loss. However, this requires both a large external magnetic field and an extremely low temperature. This is why practical applications have not been possible. Researchers believed that this problem could be overcome with new materials called topological insulators that have ferromagnetic properties such as those found in Cr-doped (Sb, Bi)2Te3.


A topological insulator, predicted in 2005 and first observed in 2007, is neither a metal nor an insulator, and has exotic properties. For example, an electric current is generated only at the surface or the edge of the material, while no electric current is generated inside it. It looks as if only the surface or the edge of the material has metallic properties, while on the inside it is an insulator. At extremely low temperatures, a thin film made of Cr-doped (Sb, Bi)2Te3 shows a peculiar phenomenon. As the film itself is ferromagnetic, an electric current is spontaneously generated without an external magnetic field and electric current flows only around the edge of the film without energy loss. However, it was previously unknown as to why Cr-doped (Sb, Bi)2Te3 had such ferromagnetic properties that allowed it to generate electric current. “That’s why we selected the material as the object of our study,” said Professor Kimura.


Because Cr is a magnetic element, a Cr atom is equivalent to an atomic-sized magnet. The N-S orientations of such atomic-sized magnets tend to be aligned in parallel by the interactions between the Cr atoms. When the N-S orientations of Cr atoms in Cr-doped (Sb, Bi)2Te3 are aligned in parallel, the material exhibits ferromagnetism. However, the interatomic distances between the Cr atoms in the material are, in fact, too long to interact sufficiently to make the material ferromagnetic.


The group found that the non-magnetic element atoms, such as the Sb and Te atoms, mediate the magnetic interactions between Cr atoms and serve as the glue to fix the N-S orientations of Cr atoms that face one direction. In addition, the group expects that its finding will provide a way to increase the critical temperature for relevant device applications.


The experiments for this research were mainly conducted at SPring-8. “We would not have achieved perfect results without the facilities and the staff there. They devoted themselves to detecting the extremely subtle magnetism that the atoms of non-magnetic elements exhibit with extremely high precision. I greatly appreciate their efforts,” Kimura said.

more...
No comment yet.
Rescooped by Dr. Stefan Gruenwald from Systems Theory
Scoop.it!

Closing the Door on Einstein and Bohr’s Quantum Debate

Closing the Door on Einstein and Bohr’s Quantum Debate | Amazing Science | Scoop.it
By closing two loopholes at once, three experimental tests of Bell’s inequalities remove the last doubts that we should renounce local realism. They also open the door to new quantum information technologies.


In 1935, Albert Einstein, Boris Podolsky, and Nathan Rosen (EPR) wrote a now famous paper questioning the completeness of the formalism of quantum mechanics. Rejecting the idea that a measurement on one particle in an entangled pair could affect the state of the other—distant—particle, they concluded that one must complete the quantum formalism in order to get a reasonable, “local realist,” description of the world. This view says a particle carries with it, locally, all the properties determining the results of any measurement performed on it. The ensemble of these properties constitutes the particle’s physical reality.

It wasn’t, however, until 1964 that John Stewart Bell, a theorist at CERN, discovered inequalities that allow an experimental test of the predictions of local realism against those of standard quantum physics. In the ensuing decades, experimentalists performed increasingly sophisticated tests of Bell’s inequalities. But these tests have always had at least one “loophole,” allowing a local realist interpretation of the experimental results unless one made a supplementary (albeit reasonable) hypothesis.

Now, by closing the two main loopholes at the same time, three teams have independently confirmed that we must definitely renounce local realism [13]. Although their findings are, in some sense, no surprise, they crown decades of experimental effort. The results also place several fundamental quantum information schemes, such as device-independent quantum cryptography and quantum networks, on firmer ground.


It is sometimes forgotten that Einstein played a major role in the early development of quantum physics [4]. He was the first to fully understand the consequences of the energy quantization of mechanical oscillators, and, after introducing “lichtquanten‚” in his famous 1905 paper, he enunciated as early as 1909 the dual wave-particle nature of light [5]. Despite his visionary understanding, he grew dissatisfied with the “Copenhagen interpretation” of the quantum theory, developed by Niels Bohr, and tried to find an inconsistency in the Heisenberg uncertainty relations. At the Solvay conference of 1927, however, Bohr successfully refuted all of Einstein’s attacks, making use of ingenuous gedankenexperiments bearing on a single quantum particle.


But in 1935, Einstein raised a new objection about the Copenhagen interpretation, this time with a Gedankenexperiment involving two particles. He had discovered that the quantum formalism allows two particles to be entangled in a state such that strong correlations are predicted between measurements on these two particles. These correlations would persist at particle separations large enough that the measurements could not be directly connected by any influence, unless it were to travel faster than light. Einstein therefore argued for what he felt was the only reasonable description: that each particle in the pair carries a property, decided at the moment of separation, which determines the measurement results. But since entangled particles are not described separately in the quantum formalism, Einstein concluded the formalism was incomplete [6]. Bohr, however, strongly opposed this conclusion, convinced that it was impossible to complete the quantum formalism without destroying its self-consistency


Via Ben van Lier
more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

Time Unidirectionally Moving Forward Even In The Quantum World

Time Unidirectionally Moving Forward Even In The Quantum World | Amazing Science | Scoop.it
Physicists have proven that the laws of thermodynamics work in the quantum world. This discovery has huge implications for technologies currently being developed, such as quantum computers. 

Researchers created an experiment in which they showed the irreversibility of a quantum mechanical process. They created an isolated quantum system and measured the change in entropy – defined as a gradual decline into disorder – when applying an oscillating magnetic field. If the process was reversible, the entropy wouldn’t increase and move towards disorder, but in reality it does. The team link this finding to the concept of the arrow of time.

We don’t know why time passes. We think that the arrow of time has a direction due to the second law of thermodynamics. The law states that the entropy of the universe always increases, with the entropy being the level of disorder of a system. Basically, the second law says that you can’t perfectly put back together a broken vase. If we see a broken vase, we know that it was broken in the past. 

Quantum mechanics has so far avoided being affected by thermodynamics. Most of the quantum laws are perfectly symmetric in time. “Quantum vases” break apart and jump back together and both situations are perfectly allowed. But this experiment showed that thermodynamics affects the quantum world as well and that the arrow of time arises naturally from the fundamental laws of the universe. 

In the experiment, the scientists measured the entropy of a sample of liquid chloroform. The substance is useful because the spin of the nucleus of the hydrogen atom couples with the spin of the nucleus of the carbon atom. A variable magnetic field was applied to the system, and every time the magnetic field would reverse, the spin would flip. 

The changes in the magnetic field were so rapid that the spins stopped keeping up with it and they ceased being in equilibrium, letting the entropy of the system increase. 

The researchers think that the lack of equilibrium arises directly from the initial condition of the system. The laws of quantum mechanics always start with systems in perfect equilibrium, but creating such a system in reality is very difficult and all the processes we have observed so far are not truly in equilibrium. "Full and perfect reversibility is an abstraction that might be approximately achieved in very controlled situations," Mauro Paternostro, co-author of the study, told IFLScience.
more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

Scientists have figured out what we need to achieve secure quantum teleportation

Scientists have figured out what we need to achieve secure quantum teleportation | Amazing Science | Scoop.it

"We've got this."


For the first time, researchers have demonstrated the precise requirements for secure quantum teleportation – and it involves a phenomenon known 'quantum steering', first proposed by Albert Einstein and Erwin Schrödinger.


Before you get too excited, no, this doesn't mean we can now teleport humans like they do on Star Trek. Instead, this research will allow people to use quantum entanglement to send information across large distances without anyone else being able to eavesdrop. Which is almost as cool, because this is how we'll form the un-hackable communication networks of the future.


Quantum teleportation isn't new in itself. Researchers have already had a lot of success quantum teleporting information over 100 km of fiber. But there's a slight issue – the quantum message was getting to the other end kinda incoherent, and scientists haven't exactly known what to do to prevent that from happening, until now. 


"Teleportation works like a sophisticated fax machine, where a quantum state is transported from one location to another," said one of the researchers, Margaret Reid, from Swinburne University of Technology in Australia. "Let’s say 'Alice' begins the process by performing operations on the quantum state – something that encodes the state of a system – at her station. Based on the outcomes of her operations, she communicates (by telephone or public Internet) to 'Bob' at a distant location, who is then able to create a replica of the quantum state," she explains.


"The problem is that unless special requirements are satisfied, quantum mechanics demands that the state at Bob’s end will be 'fuzzed up'." The researchers have now shown that to avoid this, Alice and Bob (or anyone else who wants to send an entangled message) need to use a special form of quantum entanglement known as 'Einstein-Podolsky-Rosen steering'.


"Only then can the quality of the transported state be perfect," said Reid. "The beauty is that quantum mechanics guarantees that a perfect state can only be transported to one receiver. Any second 'eavesdropper' will get a fuzzy version." Basically, in this quantum steering state, the measurement of one entangled particle can have an immediate 'steering' effect on the state of another distant particle.

The researchers will continue to investigate this phenomenon to figure out how it can be used to more reliably communicate using quantum entanglement.

more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

Pulsar Web Could Detect Low-Frequency Gravitational Waves

Pulsar Web Could Detect Low-Frequency Gravitational Waves | Amazing Science | Scoop.it
Monitoring a vast network of rapidly spinning pulsars is key to finding very-low-frequency gravitational waves, researchers say.


Pulsars emit beams of radio waves, some of which sweep across Earth once every rotation. Astronomers detect this as a rapid pulse of radio emission. Most pulsars rotate several times a second. But some, called millisecond pulsars, rotate hundreds of times faster.


"Millisecond pulsars have extremely predictable arrival times, and our instruments are able to measure them to within a ten-millionth of a second," said Maura McLaughlin, a radio astronomer at West Virginia University in Morgantown and member of the NANOGrav team. "Because of that, we can use them to detect incredibly small shifts in Earth's position."


But astrophysicists at JPL and Caltech caution that detecting faint gravitational waves would likely require more than a few pulsars. "We're like a spider at the center of a web," said Michele Vallisneri, another member of the JPL/Caltech research group. "The more strands we have in our web of pulsars, the more likely we are to sense when a gravitational wave passes by."


Vallisneri said accomplishing this feat will require international collaboration. "NANOGrav is currently monitoring 54 pulsars, but we can only see some of the southern hemisphere. We will need to work closely with our colleagues in Europe and Australia in order to get the all-sky coverage this search requires."


The feasibility of this approach was recently called into question when a group of Australian pulsar researchers reported that they were unable to detect such signals when analyzing a set of pulsars with the most precise timing measurements. After studying this result, the NANOGrav team determined that the reported non-detection was not a surprise, and resulted from the combination of optimistic gravitational wave models and analysis of too few pulsars. Theirone-page response was released recently via the arXiv electronic print service.


Despite the technical challenges, Taylor is confident their team is on the right track. "Gravitational waves are washing over Earth all the time," Taylor said. "Given the number of pulsars being observed by NANOGrav and other international teams, we expect to have clear and convincing evidence of low-frequency gravitational waves within the next decade."


NANOGrav is a collaboration of over 60 scientists at more than a dozen institutions in the United States and Canada. The group uses radio pulsar timing observations acquired at NRAO's Green Bank Telescope in West Virginia and at Arecibo Radio Observatory in Puerto Rico to search for ripples in the fabric of spacetime. In 2015, NANOGrav was awarded $14.5 million by the National Science Foundation to create and operate a Physics Frontiers Center.


"With the recent detection of gravitational waves by LIGO, the outstanding work of the NANOGrav collaboration is particularly relevant and timely," said Pedro Marronetti, National Science Foundation program director for gravitational wave research. "This NSF-funded Physics Frontier Center is poised to complement LIGO observations, extending the window of gravitational wave detection to very low frequencies."

more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

Three new gravitational wave projects unveiled in China

Three new gravitational wave projects unveiled in China | Amazing Science | Scoop.it
Chinese scientists have unveiled three separate projects to investigate gravitational waves, state media said Wednesday, days after earthshaking US discoveries that confirmed Einstein's century-old predictions.


Space officials said such research would give China—which has an ambitious, military-run, multi-billion-dollar space programme that Beijing sees as symbolising the country's progress—an opportunity to become a "world leader" in the field.


Gravitational waves are direct evidence of ripples in the fabric of space-time, and their first-ever observation was announced by US scientists last week. The Chinese Academy of Sciences (CAS) rolled out a proposal for a space-based gravitational wave detection project, the official Xinhua news agency reported.


The proposed Taiji programme, named after the "supreme ultimate" of Chinese philosophy symbolised by the yin-yang sign, would send satellites of its own into orbit or share equipment with the European Space Agency's eLISA initiative.


Separately, Sun Yat-sen University in Guangzhou also proposed to launch satellites into space, while the Institute of High Energy Physics at CAS suggested a land-based scheme in Tibet. All three projects have yet to obtain government approval, state media said.

more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

A Toolkit for Silicon-based Quantum Computing

A Toolkit for Silicon-based Quantum Computing | Amazing Science | Scoop.it
Before quantum computing becomes practical, researchers will need to find a practical way to store information as quantum bits, or qubits. Researchers are making significant progress toward the creation of electronic devices based on qubits made of single ions implanted in silicon, one of the most practical of all materials.


“Bit” is a contraction of “binary digit,” but unlike a classical bit, which is plain-vanilla binary with a value of either 0 or 1, a quantum bit, or qubit — the theoretical basis of quantum computing — holds both 0 and 1 in a superposed state until it is measured.


A vast computational space can be created with relatively few quantum-mechanically entangled qubits, and the measurement of one qubit can instantly resolve an intricate calculation when all the entangled qubits are “collapsed” to a specific value by the measurement.


So how does one make and measure a qubit? The problem has engaged scientists for years. Many arrangements have been proposed and some demonstrated, each with its advantages and disadvantages, including tricky schemes involving superconducting tunnel junctions, quantum dots, neutral atoms in optical lattices, trapped ions probed by lasers, and so on.


In the long run, however, qubits based on individual dopant atoms implanted in silicon may have the edge. The materials and methods of silicon-chip manufacturing are familiar and, when applied to quantum-computer devices, have the potential for easy scale-up.


“There are three pillars to the development program my colleagues and I have been following,” says Thomas Schenkel of Berkeley Lab’s Accelerator and Fusion Research Division. “One is the theory of quantum measurement in the devices we build, led by Professor Birgitta Whaley from the Department of Chemistry at UC Berkeley; another is the fabrication of these devices, headed by myself and Professor Jeff Bokor from UC Berkeley’s Department of Electrical Engineering and Computer Science; and the third is to actually measure quantum states in these devices, an effort led by Professor Steve Lyon from Princeton’s Department of Electrical Engineering. Of course, things don’t necessarily happen in that order.”

more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

Revolutionizing heat transport: Quantum-limited heat conduction over macroscopic distances

Revolutionizing heat transport: Quantum-limited heat conduction over macroscopic distances | Amazing Science | Scoop.it

Scientists at Aalto University, Finland, have made a breakthrough in physics. They succeeded in transporting heat maximally effectively ten thousand times further than ever before. The discovery may lead to a giant leap in the development of quantum computers.


Heat conduction is a fundamental physical phenomenon utilized, for example, in clothing, housing, car industry, and electronics. Thus our day-to-day life is inevitably affected by major shocks in this field. The research group, led by quantum physicist Mikko Möttönen has now made one of these groundbreaking discoveries. This new invention revolutionizes quantum-limited heat conduction which means as efficient heat transport as possible from point A to point B. This is great news especially for the developers of quantum computers.


Quantum technology is still a developing research field, but its most promising application is the super-efficient quantum computer. In the future, it can solve problems that a normal computer can never crack. The efficient operation of a quantum computer requires that it can be cooled down efficiently. At the same time, a quantum computer is prone to errors due to external noise.


Möttönen's innovation may be utilized in cooling quantum processors very efficiently and so cleverly that the operation of the computer is not disturbed.


"Our research started already in 2011 and advanced little by little. It feels really great to achieve a fundamental scientific discovery that has real practical applications", Professor Mikko Möttönen rejoices.


In the QCD Labs in Finland, Möttönen's research group succeeded in measuring quantum-limited heat transport over distances up to a meter. A meter doesn't sound very long at first, but previously scientists have been able to measure such heat transport only up to distances comparable to the thickness of a human hair.


"For computer processors, a meter is an extremely long distance. Nobody wants to build a larger processor than that", stresses Möttönen.

more...
No comment yet.
Rescooped by Dr. Stefan Gruenwald from Fragments of Science
Scoop.it!

Physicists control electrons at femtosecond timescales

Physicists control electrons at femtosecond timescales | Amazing Science | Scoop.it

When you shine a light on a conducting surface like silicon or graphene, that light jump-starts certain electrons into high-energy states and kicks off a cascade of interactions that happens faster than the blink of an eye. Within just a few femtoseconds — a thousand trillionth of a second — these energized electrons can scatter among other electrons like balls on a billiard table, quickly dissipating energy in an ultrafast process known as thermalization.


Now physicists at MIT have come up with a way to manipulate electrons in graphene within the first few femtoseconds of photo-excitation. With their technique, the researchers can redirect these high-energy electrons before they interact with other electrons in the material. The team’s ultrafast control of high-energy electrons may ultimately lead to more efficient photovoltaic and energy-harvesting devices, which capture photo-excited electrons before they lose their energy to thermalization.


“We’re intellectually excited about whether this will have technological applications,” says Pablo Jarillo-Herrero, associate professor of physics at MIT. “It’s too soon to know, but there are certain angles of looking at this where it's clear there might be ways to engineer energy flow or transfer in ways that are novel. Now we need more people thinking about this.”


The group’s results are published this week in the journal Nature Physics. Jarillo-Herrero’s co-authors include lead author and graduate student Qiong Ma, along with Jing Kong, professor of electrical engineering and computer science, and Nuh Gedik, associate professor of physics.


Via Mariaschnee
more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

The very first experimental observations of knots in quantum matter have just been reported

The very first experimental observations of knots in quantum matter have just been reported | Amazing Science | Scoop.it

The very first experimental observations of knots in quantum matter have just been reported in Nature Physics by scientists at Aalto University (Finland) and Amherst College (USA). The scientists created knotted solitary waves, or knot solitons, in the quantum-mechanical field describing a gas of superfluid atoms, also known as a Bose-Einstein condensate.


In contrast to knotted ropes, the created quantum knots exist in a field that assumes a certain direction at every point of space. The field segregates into an infinite number of linked rings, each with its own field direction. The resulting structure is topologically stable as it cannot be separated without breaking the rings. In other words, one cannot untie the knot within the superfluid unless one destroys the state of the quantum matter.


To make this discovery, the scientists tied the knot by squeezing the structure into the condensate from its outskirts. This required them to initialize the quantum field to point in a particular direction, after which they suddenly changed the applied magnetic field to bring an isolated null point, at which the magnetic field vanishes, into the center of the cloud. Then they just waited for less than a millisecond for the magnetic field to do its trick and tie the knot.


For decades, physicists have been theoretically predicting that it should be possible to have knots in quantum fields, but nobody else has been able to make one. "Now that we have seen these exotic beasts, we are really excited to study their peculiar properties. Importantly, our discovery connects to a diverse set of research fields including cosmology, fusion power, and quantum computers", says research group leader Mikko Möttönen, Aalto University.


Knots have been used and appreciated by human civilizations for thousands of years. For example, they have enabled great seafaring expeditions and inspired intricate designs and patterns. The ancient Inca civilization used a system of knots known as quipu to store information. In modern times, knots have been thought to play important roles in the quantum-mechanical foundations of nature, although they have thus far remained unseen in quantum dynamics.


In everyday life, knots are typically tied on ropes or strings with two ends. However, these kinds of knots are not what mathematicians call topologically stable since they can be untied without cutting the rope. In stable knots, the ends of the ropes are glued together. Such knots can be relocated within the rope but cannot be untied without scissors.


Mathematically speaking, the created quantum knot realizes a mapping referred to as Hopf fibration that was discovered by Heinz Hopf in 1931. The Hopf fibration is still widely studied in physics and mathematics. Now it has been experimentally demonstrated for the first time in a quantum field.

more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

Physicists discover new fundamental quantum mechanical property

Physicists discover new fundamental quantum mechanical property | Amazing Science | Scoop.it

Nanotechnologists at the University of Twente research institute MESA+ have discovered a new fundamental property of electrical currents in very small metal circuits. They show how electrons can spread out over the circuit like waves and cause interference effects at places where no electrical current is driven. The geometry of the circuit plays a key role in this so called nonlocal effect. The interference is a direct consequence of the quantum mechanical wave character of electrons and the specific geometry of the circuit. For designers of quantum computers it is an effect to take account of. The results are published in the British journal Scientific Reports.


Interference is a common phenomenon in nature and occurs when one or more propagating waves interact coherently. Interference of sound, light or water waves is well known, but also the carriers of electrical current – electrons – can interfere. It shows that electrons need to be considered as waves as well, at least in nanoscale circuits at extremely low temperatures: a canonical example of the quantum mechanical wave-particle duality.


The researchers from the University of Twente have demonstrated electron interference in a gold ring with a diameter of only 500 nanometers (a nanometer is a million times smaller than a millimeter). One side of the ring was connected to a miniature wire through which an electrical current can be driven. On the other side, the ring was connected to a wire with a voltmeter attached to it. When a current was applied, and a varying magnetic field was sent through the ring, the researchers detected electron interference at the other side of the ring, even though no net current flowed through the ring.


This shows that the electron waves can "leak" into the ring, and change the electrical properties elsewhere in the circuit, even when classically one does not expect anything to happen. Although the gold ring is diffusive (meaning that the electron mean free path is much smaller than the ring), the effect was surprisingly pronounced.

more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

The physics of life: From flocking birds to swarming molecules - in search for a fundamental theory

The physics of life: From flocking birds to swarming molecules - in search for a fundamental theory | Amazing Science | Scoop.it
From flocking birds to swarming molecules, physicists are seeking to understand 'active matter' — and looking for a fundamental theory of the living world.


First, Zvonimir Dogic and his students took microtubules — threadlike proteins that make up part of the cell's internal 'cytoskeleton' — and mixed them with kinesins, motor proteins that travel along these threads like trains on a track. Then the researchers suspended droplets of this cocktail in oil and supplied it with the molecular fuel known as adenosine triphosphate (ATP). To the team's surprise and delight, the molecules organized themselves into large-scale patterns that swirled on each droplet's surface. Bundles of microtubules linked by the proteins moved together “like a person crowd-surfing at a concert”, says Dogic, a physicist at Brandeis University in Waltham, Massachusetts.


With these experiments, published1 in 2012, Dogic's team created a new kind of liquid crystal. Unlike the molecules in standard liquid-crystal displays, which passively form patterns in response to electric fields, Dogic's components were active. They propelled themselves, taking energy from their environment — in this case, from ATP. And they formed patterns spontaneously, thanks to the collective behavior of thousands of units moving independently.


Researchers hope that this work will lead them to a complete, quantitative theory of active matter. Such a theory would build on physicists' century-old theory of statistical mechanics, which explains how the motion of atoms and molecules gives rise to everyday phenomena such as heat, temperature and pressure. But it could go much further, providing a mathematical framework for still-mysterious biological processes such as how cells move things around, how they create and maintain their shapes and how they divide. “We want a theory of the mechanics and statistics of living matter with a status comparable to what's already been done for collections of dead particles,” says Sriram Ramaswamy, a physicist and director of the Tata Institute of Fundamental Research's Centre for Interdisciplinary Sciences in Hyderabad, India.


All known life forms are based on self-propelled entities uniting to create large-scale structures and movements. If this didn't happen, organisms would be limited to using much slower, passive processes such as diffusion to move DNA and proteins around inside cells or tissues, and many of life's complex structures and functions might never have evolved. Biologists and physicists have speculated for decades about the general principles of living matter, but research on cellular processes has focused on identifying the dizzying array of molecules involved, rather than on working out the principles by which they self-organize. As a result, what is now known as active-matter research did not really get under way until the mid-1990s.


One of the most influential early experiments was conducted by the team of Stanislas Leibler, a biophysicist who was then at Princeton University in New Jersey and is now at the Rockefeller University in New York. The group was among the first to show that complex, life-like structures could self-assemble from microtubules and a few proteins supplied with ATP2. Around the same time, an influential model of active matter was being developed by Tamás Vicsek, a theoretical biophysicist at Eötvös Loránd University in Budapest. In the early 1990s, Vicsek was trying to account for the collective motions of bird flocks, bacterial colonies and cytoskeleton components when he realized that no existing theory would work. “It's not like equilibrium statistical mechanics, where you take a book and you find what to do,” says physicist Jean-François Joanny of the Curie Institute in Paris.

Instead, Vicsek found a starting point in a model of magnetic materials developed in 1928 by German physicist Werner Heisenberg. Heisenberg imagined each atom as a freely rotating bar magnet, and found that large-scale magnetism emerges when interactions between these atomic magnets cause the majority of them to align. To explain active matter, Vicsek replaced the tiny magnets with moving 'arrows' symbolizing particles with velocities that aligned with the average velocity of their neighbours — albeit with a certain amount of random error. That led to what is now known as Vicsek's flocking model3. His simulations showed that when enough arrows were packed into a small enough space, they began to move in patterns that closely resembled the familiar movements of bird flocks and fish schools (see 'Smart swarms').

more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

New half-meter record for quantum superposition at macroscopic level

New half-meter record for quantum superposition at macroscopic level | Amazing Science | Scoop.it

A team of researchers working at Stanford University has extended the record for quantum superposition at the macroscopic level, from 1 to 54 centimeters. In their paper published in the journal Nature, the team describes the experiment they conducted, their results and also discuss what their findings might mean for researchers looking to find the cutoff point between superposition as it applies to macroscopic objects versus those that only exist at the quantum level. Nature has also published an editorial on the work done by the team, describing their experiment and summarizing their results.


Scientists entangling quantum particles and even whole atoms has been in the news a lot over the past couple of years as experiments have been conducted with the goal of attempting to better understand the strange phenomenon—and much has been learned. But, as scientists figure out how to entangle two particles at ever greater distances apart there has come questions about the size of objects that can be entangled. Schrödinger's cat has come up in several such discussions as theorists and those in the applied fields seek to figure out if it might be truly possible to cause a whole cat to actually be in two places at once. In this new work, the team at Stanford has perhaps muddied the water even more as they have extended the record for supposition from a mere one centimeter to just over half a meter.


They did it by creating a Bose-Einstein condensate cloud made up of 10,000 rubidium atoms (inside of a super-chilled chamber) all initially in the same state. Next, the used lasers to push the cloud up into the 10 meter high chamber, which also caused the atoms to enter one or the other of a given state. As the cloud reached the top of the chamber, the researchers noted that the wave function was a half-and-half mixture of the given states and represented positions that were 54 centimeters apart. When the cloud was allowed to fall back to the bottom of the chamber, the researchers confirmed that atoms appeared to have fallen from two different heights, proving that the cloud was held in a superposition state.


The team acknowledges that while their experiment has led to a new record for superposition at the macroscopic scale, it still was done with individual atoms, thus, it is still not clear if superposition will work with macroscopic sized objects.

more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

Giant enhancement of magnetic effect will benefit spintronics

Giant enhancement of magnetic effect will benefit spintronics | Amazing Science | Scoop.it

Researchers have demonstrated that coating a cobalt film in graphene doubles the film's perpendicular magnetic anisotropy (PMA), so that it reaches a value 20 times higher than that of traditional metallic cobalt/platinum multilayers that are being researched for this property.


In a material with a high PMA, the magnetization is oriented perpendicular to the interface of the material's layers. High-PMA materials are being researched for their applications in next-generation spintronic devices, such as high-density memories and heat-tolerant logic gates.


In general, spintronic devices work by using magnetic and electric fields to switch electron spins between their two states, which allows the spins to be used as binary information carriers. One of the goals in this area is to reduce the size of spintronic devices while achieivng long-term information retention of 10-plus years. In order to do this, the storage material must have a large PMA.


"Perpendicular magnetic anisotropy (PMA) at ferromagnetic transition-metal/insulator interfaces has become of huge interest in the context of development of various spintronic devices," coauthor Mairbek Chshiev, a theoretical physicist and professor at Joseph Fourier University in Grenoble, France, told Phys.org. "Enhancement of effective PMA could be achieved either by increasing the surface PMA or by minimizing the saturation magnetization of the storage layer. The co-graphene heterostructures presented in the manuscript benefits from both these properties."


As the researchers explain in their paper, the PMA enhancement in the graphene-coated cobalt films originates at the atomic level, where graphene affects the energy of cobalt's different electron orbitals. The graphene coating changes how these orbitals overlap with one another, which in turn changes the direction of the cobalt film's overall magnetic field: some of the magnetization that was originally parallel to the film surface is now oriented perpendicular to the film surface.

more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

Physicists continue to investigate why the universe did not collapse shortly after big bang

Physicists continue to investigate why the universe did not collapse shortly after big bang | Amazing Science | Scoop.it

According to the best current physics models, the universe should have collapsed shortly after inflation—the period that lasted for a fraction of a second immediately after the Big Bang.


The problem lies in part with Higgs bosons, which were produced during inflation and which explain why other particles have the masses that they do. Previous research has shown that, in the early universe, the Higgs field may have acquired large enough fluctuations to overcome an energy barrier that caused the universe to transition from its standard vacuum state to a negative energy vacuum state, which would have caused the universe to quickly collapse in on itself.


In a new paper published in Physical Review Letters, Matti Herranen at the University of Copenhagen and coauthors may have come a step closer to solving the problem by constraining the strength of the coupling between the Higgs field and gravity, which is the last unknown parameter of the standard model.


As the physicists explain, the stronger the Higgs field is coupled to gravity, the larger are the fluctuations that may eventually trigger a fatal transition to the negative energy vacuum state.


In the new paper, the scientists calculated that a collapse after inflation would have happened only if the coupling strength had been above a value of 1. Combining this result with the lower bound of 0.1, which the same physicists derived last year by analyzing the requirements for stability during (rather than after) inflation, and the range of 0.1-1 constrains the coupling to near its historically estimated value of 1/6.


This value of 1/6 is traditionally used as an estimate because it corresponds to zero Higgs-gravity coupling, though it is likely incorrect. Narrowing down the Higgs-gravity coupling strength will guide physicists when analyzing experimental data to help pinpoint the coupling value with greater precision. Data on the cosmic microwave background radiation and gravitational waves, for example, are expected to help further constrain the value. When combined with other parameters, the Higgs-gravity coupling strength should produce a picture of a universe that did not transition to a state of collapse.

more...
No comment yet.
Scooped by Dr. Stefan Gruenwald
Scoop.it!

LHC sees hint of boson heavier than Higgs (750 GeV)

LHC sees hint of boson heavier than Higgs (750 GeV) | Amazing Science | Scoop.it
Tantalizing results from upgraded collider will be followed up within a year.


The two experiments that discovered the Higgs boson in 2012 have sensed an intriguing — if very preliminary — whiff of a possible new elementary particle. Both collaborations announced their observations on 15 December, as they released their first significant results since a major upgrade of the Large Hadron Collider (LHC) outside Geneva, Switzerland, was completed earlier this year.


The results largely match a rumour that has been circulating on social media and blogs for several days: that both the CMS and ATLAS detectors at the LHC have seen an unexpected excess of pairs of photons, together carrying around 750 gigaelectronvolts (GeV) of energy, in the debris of their proton–proton collisions. This could be a tell-tale sign of a new particle — also a boson, but not necessarily similar to the Higgs — decaying into two photons of equal mass. If so, the particle would be about four times more massive than the next heaviest particle discovered so far, the top quark, and six times more massive than the Higgs.


In their talks at CERN — the laboratory that hosts the LHC — the speakers for the two experiments took turns in surveying the results of the higher-energy, 'run 2' of experiments, which began in June and was suspended in early November. Both speakers left the results on photon pairs for the end of their talks.


In both cases, the statistical significances were very low. Marumi Kado of the Linear Accelerator Laboratory at the University of Paris-Sud said that his experiment, ATLAS, had detected about 40 more pairs of photons than would have been expected from the predictions of the standard model of particle physics. Jim Olsen of Princeton University in New Jersey reported that CMS saw merely ten. Neither team would have mentioned the excesses had the other experiment had not seen an almost identical hint. “It is a little intriguing,” says ATLAS spokesperson Dave Charlton of the University of Birmingham, UK. “But it can happen by coincidence.”


more...
No comment yet.