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Physicists Discover New Massless Particle; Could Revolutionize Electronics & Quantum Computing

Hasan massless particle

Physics may have just taken a new leap forward, as three independent groups of physicists have found strong evidence for massless particles called “Weyl fermions,” which exist as quasiparticles – collective excitations of electrons. Ultimately, this discovery is over 80 years in the making, dating back to Paul Dirac.

In 1928, Dirac came up with an equation that described the spin of fermions (fermions are the building blocks that make up all matter). Within his equation, he discovered that, in relation to particles that have charge and mass, there should be a another particle and antiparticle—what we know as the electron and (its antiparticle) the positron.

Yet, there are more than one ways to skin a cat.

Other solutions to this equation hinted at more exotic kinds of particles. Enter Hermann Weyl, a German mathematician who, in 1929, come up with a solution that involved massless particles. These became known as “Weyl fermions.” And, for a number of years, physicists believed that neutrinos (subatomic particles that are produced by the decay of radioactive elements) were actually Weyl particles. Yet, further studies, which were published in 1998, indicated that neutrinos do, in fact, have mass, which means that they cannot be the aforementioned Weyl particles.

But now, we have evidence that Weyl fermions actually exist.

Unlocking the Find

The research comes thanks to Zahid Hasan over at Princeton University, who uncovered these particles in the semimetal tanatalum arsenide (which is referred to as TaAs). Hasan and his team suggested that  TaAs should contain Weyl fermions and (here is the important bit) it should have what is known as a “Fermi arc.” And in 2014, the team found evidence of such an arc.

Artist's rendition via ChutterStock

But that’s not all, another team, led by Hongming Weng at the Chinese Academy of Sciences, found similar evidence in an independent study that used the same methods. And Marin Soljačić and colleagues (hailing from MIT and the Univeristy of China) have seen evidence of Weyl fermions in a different material, specifically, a “double-gyroid” photonic crystal.

In this latter case, the team fired microwaves at the crystal and measured microwave transmission through it, varying the frequency of the microwaves throughout the experiment. Through this process, the team could map the structure of the crystal, allowing them to determine which microwave frequencies can travel through the crystal and which cannot. In the end, this revealed the presence of “Weyl points” in the structure, which is strong evidence for Weyl fermion states existing within the photonic crystal.

The Future of Physics

The significance of this find, quite literally, cannot be overstated. Hasan is clear to point this out, noting in the press release that, “The physics of the Weyl fermion are so strange, there could be many things that arise from this particle that we’re just not capable of imagining now.”

He goes on to note more specific applications: “It’s like they have their own GPS and steer themselves without scattering. They will move and move only in one direction since they are either right-handed or left-handed and never come to an end because they just tunnel through. These are very fast electrons that behave like unidirectional light beams and can be used for new types of quantum computing.” Soljačić, the head of the second study, adds that, “The discovery of Weyl points is not only the smoking gun to a scientific mystery, it paves the way to absolutely new photonic phenomena and applications.”

Ultimately, it is believed Weyl fermions could be very useful, in that, because they are massless, they can conduct electric charge much faster than normal electrons. Admittedly, this same feature is exhibited by electrons in graphene. Yet, graphene is a 2D material, Weyl fermions are thought to exist in more practical 3D materials.

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World’s thinnest light bulb created from graphene

graphene-light-bulb

When a current was run through strips of graphene that were placed across a trench of silicon, the result was light emission. (Young Duck Kim/Columbia Engineering)

Graphene, a form of carbon famous for being stronger than steel and more conductive than copper, can add another wonder to the list: making light.

Researchers have developed a light-emitting graphene transistor that works in the same way as the filament in a light bulb.

“We’ve created what is essentially the world’s thinnest light bulb,” study co-author James Hone, a mechanical engineer at Columbia University in New York, said in a statement.

Scientists have long wanted to create a teensy “light bulb” to place on a chip, enabling what is called photonic circuits, which run on light rather than electric current. The problem has been one of size and temperature — incandescent filaments must get extremely hot before they can produce visible light. This new graphene device, however, is so efficient and tiny, the resulting technology could offer new ways to make displays or study high-temperature phenomena at small scales, the researchers said.

Making light

When electric current is passed through an incandescent light bulb’s filament — usually made of tungsten — the filament heats up and glows. Electrons moving through the material knock against electrons in the filament’s atoms, giving them energy. Those electrons return to their former energy levels and emit photons (light) in the process. Crank up the current and voltage enough and the filament in the light bulb hits temperatures of about 5,400 degrees Fahrenheit for an incandescent. This is one reason light bulbs either have no air in them or are filled with an inert gas like argon: At those temperatures tungsten would react with the oxygen in air and simply burn.

In the new study, the scientists used strips of graphene a few microns across and from 6.5 to 14 microns in length, each spanning a trench of silicon like a bridge. (A micron is one-millionth of a meter, where a hair is about 90 microns thick.) An electrode was attached to the ends of each graphene strip. Just like tungsten, run a current through graphene and the material will light up. But there is an added twist, as graphene conducts heat less efficiently as temperature increases, which means the heat stays in a spot in the center, rather than being relatively evenly distributed as in a tungsten filament.

Myung-Ho Bae, one of the study’s authors, told Live Science trapping the heat in one region makes the lighting more efficient. “The temperature of hot electrons at the center of the graphene is about 3,000 K [4,940 F], while the graphene lattice temperature is still about 2,000 K [3,140 F],” he said. “It results in a hotspot at the center and the light emission region is focused at the center of the graphene, which also makes for better efficiency.” It’s also the reason the electrodes at either end of the graphene don’t melt.

As for why this is the first time light has been made from graphene, study co-leader Yun Daniel Park, a professor of physics at Seoul National University, noted that graphene is usually embedded in or in contact with a substrate.

“Physically suspending graphene essentially eliminates pathways in which heat can escape,” Park said. “If the graphene is on a substrate, much of the heat will be dissipated to the substrate. Before us, other groups had only reported inefficient radiation emission in the infrared from graphene.”

The light emitted from the graphene also reflected off the silicon that each piece was suspended in front of. The reflected light interferes with the emitted light, producing a pattern of emission with peaks at different wavelengths. That opened up another possibility: tuning the light by varying the distance to the silicon.

The principle of the graphene is simple, Park said, but it took a long time to discover.

“It took us nearly five years to figure out the exact mechanism but everything (all the physics) fit. And, the project has turned out to be some kind of a Columbus’ Egg,” he said, referring to a legend in which Christopher Columbus challenged a group of men to make an egg stand on its end; they all failed and Columbus solved the problem by just cracking the shell at one end so that it had a flat bottom.

The research is detailed in the June 15 issue of Nature Nantechnology.

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Wormhole Illusion Causes Magnetic Field To Move Through Space Undetected

August 20, 2015 | by Jonathan O’Callaghan

Wormhole illustration

photo credit: An illustration of a wormhole in action. edobric/Shutterstock.

Scientists have developed a magnetic system that mimics the behavior of a wormhole – theorized to allow space-time to be bent, and vast distances to be traveled in an instant – but it absolutely is not an actual wormhole, so don’t get too excited. However, what they did, which was to make a propagating magnetic field invisible, is actually very interesting. You can get excited again.

The research, by a team from the Autonomous University of Barcelona (UAB), was published in the journal Scientific Reports. They describe how they created a small sphere about 45 millimeters (1.8 inches) across, made of a spherical ferromagnetic (one that can become magnetized) surface, a spherical superconducting layer, and an inner ferromagnetic sheet wound in a spiral. The superconducting layer was made of superconducting strips glued to a sphere, and the entire device needed to be submerged in liquid nitrogen for the superconductor to work. The magnetic field was supplied at one end by a current passing through a coil.

When the magnetic field entered the sphere at one end, the researchers showed how it would appear at the other end as an isolated monopolar-like field – but within the sphere itself, there was no trace of the magnetic field. The dual-layered design was responsible for making the magnetic field invisible; the attraction and repulsion of the magnetic field was cancelled out, making it undetectable. “Our wormhole transfers the magnetic field from one point in space to another through a path that is magnetically undetectable,” the researchers wrote in their paper.

“It disappears in one point and reappears in a different point, as if it were travelling through another dimension,” lead researcher Alvaro Sanchez added to IFLScience.

Shown is an illustration of the field entering the sphere, left, and passing out, right, like a “wormhole.” Jordi Prat-Camps and Universitat Autònoma de Barcelona.

Why is this important? It means that the magnetic field could travel from one side of the sphere to the other without producing any noticeable effects. If you placed a magnet inside the sphere, it would not be influenced by this propagating field at all. Of course, in this case the magnetic field is actually very much there in the sphere – it’s just not detectable. In an actual theoretical wormhole, an object would disappear at one point in space-time and reappear at another. So this isn’t quite the real deal.

“It can be said to be like an illusion,” said Sanchez. “It’s not an actual wormhole, it’s not creating a real path in space-time that connects two points. It’s a magnetic field that achieves a similar effect.”

On the possible applications for the research, Sanchez said it could be useful for magnetic resonance imagers (MRIs) in medicine. “One could perhaps use this kind of wormhole to do simultaneous imaging,” he said. “You could have three detectors in one MRI scan to take images of the knee, liver and head. They would not interfere, because their magnetic fields would be invisible.”

The team now wants to study the same effect using different geometries. For example, they might try and use a cylinder instead of a sphere to recreate the effect, to highlight some of the more practical applications for the technique.

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Physicists see 27th dimension of photons

Physicists see 27th dimension of photons

By Jesse Emspak

Published January 29, 2014

  • photon-eye

    Scientists find a way to directly measure quantum states, such as momentum, of photons. (MPQ, Quantum Dynamics Division.)

Quantum computers and communications promise more powerful machines and unbreakable codes. But to make them work, it’s necessary to measure the quantum state of particles such as photons or atoms. Quantum states are numbers that describe particle characteristics such as momentum or energy.

But measuring quantum states is difficult and time-consuming, because the very act of doing so changes them, and because the mathematics can be complex. Now, an international team says they found a more efficient way to do it, which could make it simpler to build quantum-mechanical technologies.

In a study detailed in the Jan. 20 issue of the journal Nature Communications, researchers from the University of Rochester and the University of Glasgow took a direct measurement of a photon’s 27-dimensional quantum state. These dimensions are mathematical, not dimensions in space, and each one is a number that stores information.

To understand a 27-dimensional quantum state, think about a line described in 2 dimensions. A line would have a direction in the X and Y coordinates 3 inches left and 4 inches up, for instance. The quantum state has 27 such coordinates. [Quantum Physics: The Coolest Little Particles in Nature]

“We chose 27, kind of to make a point about 26 letters in the alphabet and throwing in one more,” said Mehul Malik, now a postdoctoral researcher at the University of Vienna. That means each quantum bit, or “qubit,” could store a letter instead of a simple 1 or 0.

Seeing a photon The group, led by Malik and Robert Boyd, a professor of optics and physics at the University of Rochester, was able to see a photon’s states directly. They measured the photon’s orbital angular momentum, which is how much the particles of light “twist” as they travel through space.

Ordinarily, finding the quantum state of a photon requires a two-step process. First, scientists have to measure some property of the photon, such as its polarization or momentum. The measurements are performed on many copies of the quantum state of a photon. But that process sometimes introduces errors. To get rid of the errors, the scientists have to look at what results they got that are “disallowed” states ones that don’t follow the laws of physics. But the only way to find them is to search through all the results and discard the ones that are impossible. That eats up a lot of computing time and effort. This process is called quantum tomography. [The 9 Biggest Unsolved Mysteries in Physics]

A light wave is a combination of an electric and magnetic field, each of which oscillates and makes a wave. Each wave moves in time with the other, and they are perpendicular to each other. A beam of light is made up of lots of these waves.

Light can have what is called orbital angular momentum. In a beam with no orbital angular momentum, the peaks of the waves the electric ones, for example are lined up. A plane connecting these peaks will be flat. If the beam has orbital angular momentum, a plane connecting these peaks will make a spiral, helical pattern, because the light waves are offset from one another slightly as you go around the beam. To measure the state of the photons, scientists must “unravel” this helical shape of the waves in the beam.

Measuring a photon’s quantum state The team first fired a laser through a piece of transparent polymer that refracted the light, “unraveling” the helix formed by the waves. The light then passed through special lenses and into a grating that makes many copies of the beam. After passing through the grating, the light is spread out to form a wider beam.

After the beam is widened, it hits a device called a spatial light modulator. The modulator carries out the first measurement. The beam then reflects back in the same direction it came from and passes through a beam splitter. At that point, part of thebeam moves toward a slit, which makes a second measurement. [Twisted Physics: 7 Mind-Blowing Experiments]

One of the two measurements is called “weak” and the other “strong.” By measuring two properties, the quantum state of the photons can be reconstructed without the lengthy error-correction calculations tomography requires.

In quantum computers, the quantum state of the particle is what stores the qubit. For instance, a qubit can be stored in the photon’s polarization or its orbital-angular momentum, or both. Atoms can also store qubits, in their momenta or spins.

Current quantum computers have only a few bits in them. Malik noted that the record is 14 qubits, using ions. Most of the time, ions or photons will only have acouple of bits they can store, as the states will be two-dimensional. Physicists use two-dimensional systems because that is what they can manipulate it would be very difficult to manipulate more than two dimensions, he said.

Direct measurement, as opposed to tomography, should make it easier to measure the states of particles (photons, in this case). That would mean it is simpler to add more dimensions three, four or even as in this experiment, 27 and store more information.

Mark Hillery, a professor of physics at Hunter College in New York, was skeptical that direct measurement would prove necessarily better than current techniques. “There is a controversy about weak measurements in particular, whether they really are useful or not,” Hillery wrote in an email to LiveScience. “To me, the main issue here is whether the technique they are using is better (more efficient) than quantum-state tomography for reconstructing the quantum state, and in the conclusion, they say they don’t really know.”

Jeff Savail, a master’s candidate researcher at Canada’s Simon Fraser University, worked on a similar direct measurement problem in Boyd’s lab, and his work was cited in Malik’s study. In an email he said one of the more exciting implications is the “measurement problem.” That is, in quantum mechanical systems the question of why some measurements spoil quantum states while others don’t is a deeper philosophical question than it is about the quantum technologies themselves.

“The direct measurement technique gives us a way to see right into the heart of the quantum state we’re dealing with,” he said. That doesn’t mean it’s not useful far from it. “There may also be applications in imaging, as knowing the wave function of the image, rather than the square, can be quite useful.”

Malik agreed that more experiments are needed, but he still thinks the advantages might be in the relative speed direct measurement offers. “Tomography reduces errors, but the post-processing [calculations] can take hours,” he said.

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Absolute Zero No longer Coldest

Science gets colder than absolute zero

By Charles Choi

Published January 04, 2013

LiveScience

  • negative-temperature-atoms.jpg

    When an object is heated, its atoms can move with different levels of energy, from low to high. With positive temperatures (blue), atoms more likely occupy low-energy states than high-energy states, while the opposite is true for negative temperatures (red). (LMU / MPQ Munich)

Absolute zero is often thought to be the coldest temperature possible. But now researchers show they can achieve even lower temperatures for a strange realm of “negative temperatures.”

Oddly, another way to look at these negative temperatures is to consider them hotter than infinity, researchers added.

This unusual advance could lead to new engines that could technically be more than 100 percent efficient, and shed light on mysteries such as dark energy, the mysterious substance that is apparently pulling our universe apart.

An object’s temperature is a measure of how much its atoms move — the colder an object is, the slower the atoms are. At the physically impossible-to-reach temperature of zero kelvin, or minus 459.67 degrees Fahrenheit (minus 273.15 degrees Celsius), atoms would stop moving. As such, nothing can be colder than absolute zero on the Kelvin scale.

Bizarro negative temperatures

To comprehend the negative temperatures scientists have now devised, one might think of temperature as existing on a scale that is actually a loop, not linear. Positive temperatures make up one part of the loop, while negative temperatures make up the other part. When temperatures go either below zero or above infinity on the positive region of this scale, they end up in negative territory. [What’s That? Your Basic Physics Questions Answered]

‘The temperature scale simply does not end at infinity, but jumps to negative values instead.’

– Ulrich Schneider, a physicist at the University of Munich in Germany

With positive temperatures, atoms more likely occupy low-energy states than high-energy states, a pattern known as Boltzmann distribution in physics. When an object is heated, its atoms can reach higher energy levels.

At absolute zero, atoms would occupy the lowest energy state. At an infinite temperature, atoms would occupy all energy states. Negative temperatures then are the opposite of positive temperatures — atoms more likely occupy high-energy states than low-energy states.

“The inverted Boltzmann distribution is the hallmark of negative absolute temperature, and this is what we have achieved,” said researcher Ulrich Schneider, a physicist at the University of Munich in Germany. “Yet the gas is not colder than zero kelvin, but hotter. It is even hotter than at any positive temperature — the temperature scale simply does not end at infinity, but jumps to negative values instead.”

As one might expect, objects with negative temperatures behave in very odd ways. For instance, energy typically flows from objects with a higher positive temperature to ones with a lower positive temperature — that is, hotter objects heat up cooler objects, and colder objects cool down hotter ones, until they reach a common temperature. However, energy will always flow from objects with negative temperature to ones with positive temperatures. In this sense, objects with negative temperatures are always hotter than ones with positive temperatures.

Another odd consequence of negative temperatures has to do with entropy, which is a measure of how disorderly a system is. When objects with positive temperature release energy, they increase the entropy of things around them, making them behave more chaotically. However, when objects with negative temperatures release energy, they can actually absorb entropy.

Negative temperatures would be thought impossible, since there is typically no upper bound for how much energy atoms can have, as far as theory currently suggests. (There is a limit to what speed they can travel — according to Einstein’s theory of relativity, nothing can accelerate to speeds faster than light.)

Wacky physics experiment

To generate negative temperatures, scientists created a system where atoms do have a limit to how much energy they can possess. They first cooled about 100,000 atoms to a positive temperature of a few nanokelvin, or billionth of a kelvin. They cooled the atoms within a vacuum chamber, which  isolated them from any environmental influence that could potentially heat them up accidentally. They also used a web of laser beams and magnetic fields to very precisely control how these atoms behaved, helping to push them into a new temperature realm. [Twisted Physics: 7 Mind-Blowing Findings]

“The temperatures we achieved are negative nanokelvin,” Schneider told LiveScience.

Temperature depends on how much atoms move — how much kinetic energy they have. The web of laser beams created a perfectly ordered array of millions of bright spots of light, and in this “optical lattice,” atoms could still move, but their kinetic energy was limited.

Temperature also depends on how much potential energy atoms have, and how much energy lies in the interactions between the atoms. The researchers used the optical lattice to limit how much potential energy the atoms had, and they used magnetic fields to very finely control the interactions between atoms, making them either attractive or repulsive.

Temperature is linked with pressure — the hotter something is, the more it expands outward, and the colder something is, the more it contracts inward. To make sure this gas had a negative temperature, the researchers had to give it a negative pressure as well, tinkering with the interactions between atoms until they attracted each other more than they repelled each other.

“We have created the first negative absolute temperature state for moving particles,” said researcher Simon Braun at the University of Munich in Germany.

New kinds of engines

Negative temperatures could be used to create heat engines — engines that convert heat energy to mechanical work, such as combustion engines — that are more than 100-percent efficient, something seemingly impossible. Such engines would essentially not only absorb energy from hotter substances, but also colder ones. As such, the work the engine performed could be larger than the energy taken from the hotter substance alone.

Negative temperatures might also help shed light on one of the greatest mysteries in science. Scientists had expected the gravitational pull of matter to slow down the universe’s expansion after the Big Bang, eventually bringing it to a dead stop or even reversing it for a “Big Crunch.” However, the universe’s expansion is apparently speeding up, accelerated growth that cosmologists suggest may be due to dark energy, an as-yet-unknown substance that could make up more than 70 percent of the cosmos.

In much the same way, the negative pressure of the cold gas the researchers created should make it collapse. However, its negative temperature keeps it from doing so. As such, negative temperatures might have interesting parallels with dark energy that may help scientists understand this enigma.

Negative temperatures could also shed light on exotic states of matter, generating systems that normally might not be stable without them. “A better understanding of temperature could lead to new things we haven’t even thought of yet,” Schneider said. “When you study the basics very thoroughly, you never know where it may end.”

The scientists detailed their findings in the Jan. 4 issue of the journal Science.

Read more: http://www.foxnews.com/science/2013/01/04/science-gets-colder-than-absolute-zero/?intcmp=trending#ixzz2H5FSxvTv

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