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Light-Powered Gyroscope is World’s Smallest and Promises a Powerful Spin for Navigation Technologies

Light-Powered Gyroscope is World’s Smallest and Promises a Powerful Spin for Navigation Technologies | Amazing Science | Scoop.it

A pair of light waves – one zipping clockwise the other counterclockwise around a microscopic track – may hold the key to creating the world’s smallest gyroscope: one a fraction of the width of a human hair. By bringing this essential technology down to an entirely new scale, a team of applied physicists hopes to enable a new generation of phenomenally compact gyroscope-based navigation systems, among other intriguing applications.


“We have found a new detection scheme that may lead to the world's smallest gyroscope,” said Li Ge, The Graduate Center and Staten Island College, City University of New York. “Though these so-called optical gyroscopes are not new, our approach is remarkable both in its super-small size and potential sensitivity.”


Ge and his colleagues – physicist Hui Cao and her student Raktim Sarma, both at Yale University in New Haven, Connecticut – recently published their results in The Optical Society’s (OSA) new high-impact journal Optica.


More than creative learning toys, gyroscopes are indispensable components in a number of technologies, including inertial guidance systems, which monitor an object’s motion and orientation. Space probes, satellites, and rockets continuously rely on these systems for accurate flight control. But like so many other essential pieces of aerospace technology, weight is a perennial problem. According to NASA, it costs about $10,000 for every pound lifted into orbit, so designing essential components that are smaller and lighter is a constant struggle for engineers and project managers.


If the size of an optical gyroscope is reduced to just a fraction of a millimeter, as is presented in the new paper, it could then be integrated into optical circuit boards, which are similar to a conventional electric circuit board but use light to carry information instead of electric currents. This could drastically reduce the equipment cost in space missions, opening the possibility for a new generation of micro-payloads.

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A scientific first: Quantum teleportation on a photonic chip

A scientific first: Quantum teleportation on a photonic chip | Amazing Science | Scoop.it

Qubits (quantum bits) are sensitive quantum versions of today's computer 0's and 1's (bits) and are the foundation of quantum computers. Photons are particles of light and they are a promising way to implement excellent qubits. One of the most important tasks is to successfully enable quantum teleportation, which transfers qubits from one photon to another. However, the conventional experimental implementation of quantum teleportation fills a laboratory and requires hundreds of optical instruments painstakingly aligned, a far cry from the scale and robustness of device required in a modern day computer or handheld device.


In 2013, Professor Furusawa and his colleagues succeeded in realizing perfect quantum teleportation, however, this required a set-up covering several square meters; took many months to build, and reached the limit in terms of scalability. New research at the University of Bristol led by Professor Jeremy O'Brien has taken those optical circuits and implemented them on to a silicon microchip measuring just a few millimetres (0.0001 square metres) using state-of-the-art nano-fabrication methods. This is the first time quantum teleportation has been demonstrated on a silicon chip and the result has radically solved the problem of scalability. The team of researchers have taken a significant step closer towards their ultimate goal of integrating a quantum computer into a photonic chip.


While there has been significant progress in current computing technology, its performance is now reaching the fundamental limit of classical physics. On the other hand, it has been predicted that principles of quantum mechanics will enable the development of ultra-secure quantum communication and ultra-powerful quantum computers, overcoming the limit of current technologies. One of the most important steps in achieving this is to establish technologies for quantum teleportation (transferring signals of quantum bits in photons from a sender to a receiver at a distance). The implementation of teleportation on to a micro-chip is an important building block unlocking the potential for practical quantum technologies.


Professor Akira Furusawa from the University of Tokyo said: "This latest achievement enables us to perform the perfect quantum teleportation with a photonic chip. The next step is to integrate whole the system of quantum teleportation."


Professor Jeremy O'Brien, Director of the Centre for Quantum Photonics at the University of Bristol, who led the Bristol elements of the research, said: "Being able to replicate an optical circuit which would normally require a room sized optical table on a photonic chip is a hugely significant achievement. In effect, we have reduced a very complex quantum optical system by ten thousand in size."

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For the first time, ‘Spooky action at a distance’ demonstrated in single-particle quantum experiment

For the first time, ‘Spooky action at a distance’ demonstrated in single-particle quantum experiment | Amazing Science | Scoop.it
A team of scientists have for the first time successfully demonstrated the non-local collapse of a particle’s wave function in an experiment using a single particle.

Using homodyne detectors to measure the particle, and quantum tomography to map the effect of those measurements, the scientists, from Griffith University and the University of Tokyo, were able to verify single-particle quantum entanglement an unusual form of entanglement that could prove invaluable for quantum computing and communications.

While quantum entanglement usually refers to two particles that are bound by opposing spins, the directions of which will only be set when they are observed, single particles can also be entangled, meaning their wave function – ie the equation that defines their likely location and behaviour – can cover any distance.

In other words, a single entangled particle can only be in one place at a given time, but it can be located over a very large distance. When the particle is measured, the wave function will instantly collapse to a set location.


This was demonstrated by the scientists, who split a single photon between their labs in Japan and Australia, but was previously regarded as an unlikely phenomenon by Albert Einstein.


Almost 90 years ago, he used single-particle entanglement as evidence that quantum mechanics was incorrect, deriding non-local wave function collapse as “spooky action at a distance”.


“Einstein never accepted orthodox quantum mechanics and the original basis of his contention was this single-particle argument,” explained Professor Howard Wiseman, director of Griffith University’s Centre for Quantum Dynamics.


The research was published recently in Nature Communications.


Reference: Fuwa M, Takeda S, Zwierz M, Wiseman HM, Furusawa A. Experimental proof of nonlocal wavefunction collapse for a single particle using homodyne measurements. Nature Communications 06 March 2015. doi:10.1038/ncomms7665.

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Scientists make breakthrough in understanding how to control intense heat bursts in fusion experiments

Scientists make breakthrough in understanding how to control intense heat bursts in fusion experiments | Amazing Science | Scoop.it

Researchers from General Atomics and the U.S. Department of Energy's Princeton Plasma Physics Laboratory (PPPL) have made a major breakthrough in understanding how potentially damaging heat bursts inside a fusion reactor can be controlled. Scientists performed the experiments on the DIII-D National Fusion Facility, a tokamak operated by General Atomics in San Diego. The findings represent a key step in predicting how to control heat bursts in future fusion facilities including ITER, an international experiment under construction in France to demonstrate the feasibility of fusion energy.


The studies build upon previous work pioneered on DIII-D showing that these intense heat bursts - called "ELMs" for short - could be suppressed with tiny magnetic fields. These tiny fields cause the edge of the plasma to smoothly release heat, thereby avoiding the damaging heat bursts. But until now, scientists did not understand how these fields worked. "Many mysteries surrounded how the plasma distorts to suppress these heat bursts," said Carlos Paz-Soldan, a General Atomics scientist and lead author of the first of the two papers that report the seminal findings back-to-back in the same issue of Physical Review Letters this week.


Paz-Soldan and a multi-institutional team of researchers found that tiny magnetic fields applied to the device can create two distinct kinds of response, rather than just one response as previously thought. The new response produces a ripple in the magnetic field near the plasma edge, allowing more heat to leak out at just the right rate to avert the intense heat bursts. Researchers applied the magnetic fields by running electrical current through coils around the plasma. Pickup coils then detected the plasma response, much as the microphone on a guitar picks up string vibrations.


The second result, led by PPPL scientist Raffi Nazikian, who heads the PPPL research team at DIII-D, identified the changes in the plasma that lead to the suppression of the large edge heat bursts or ELMs. The team found clear evidence that the plasma was deforming in just the way needed to allow the heat to slowly leak out. The measured magnetic distortions of the plasma edge indicated that the magnetic field was gently tearing in a narrow layer, a key prediction for how heat bursts can be prevented. "The configuration changes suddenly when the plasma is tapped in a certain way," Nazikian said, "and it is this response that suppresses the ELMs."

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Superconductivity Record Broken with highest critical temperature of superconductivity in cuprates: 133˚ K

Superconductivity Record Broken with highest critical temperature of superconductivity in cuprates: 133˚ K | Amazing Science | Scoop.it

For nearly 30 years, the search for a room-temperature superconductor has focused on exotic materials known as cuprates, which can carry currents without losing energy as heat at temperatures up to 164 Kelvin, or –109 ˚C. But scientists say that they have trumped that record using the common molecule hydrogen sulphide. When they subjected a tiny sample of that material to pressures close to those inside Earth’s core, the researchers say that it was superconductive at 190 K (–83 ˚C).


"If the result is reproduced, it will be quite shocking," says Robert Cava, a solid-state chemist at Princeton University in New Jersey. "It would be a historic discovery."

The highest critical temperature of superconductivity Tc has been achieved in cuprates: 133 K at ambient pressure and 164 K at high pressures. As the nature of superconductivity in these materials is still not disclosed, the prospects for a higher Tc are not clear. In contrast the Bardeen-Cooper-Schrieffer (BCS) theory gives a clear guide for achieving high Tc: it should be a favorable combination of high frequency phonons, strong coupling between electrons and phonons, and high density of states. These conditions can be fulfilled for metallic hydrogen and covalent hydrogen dominant compounds.


Numerous followed calculations supported this idea and predicted Tc=100-235 K for many hydrides but only moderate Tc~17 K has been observed experimentally. A group of scientists now found that sulfur hydride transforms at P~90 GPa to metal and superconductor with Tc increasing with pressure to 150 K at ~200 GPa. This is in general agreement with recent calculations of Tc~80 K for H2S. Moreover they found superconductivity with Tc~190 K in a H2S sample pressurized to P>150 GPa at T>220 K. This superconductivity likely associates with the dissociation of H2S, and formation of SHn (n>2) hydrides. They reported that they have proved occurrence of superconductivity by the drop of the resistivity at least 50 times lower than the copper resistivity, the decrease of Tc with magnetic field, and the strong isotope shift of Tc in D2S which evidences a major role of phonons in the superconductivity. H2S is a substance with a moderate content of hydrogen therefore high Tc can be expected in a wide range of hydrogen-contain materials. Hydrogen atoms seem to be essential to provide the high frequency modes in the phonon spectrum and the strong electron-phonon coupling.

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Imaging the 3D structure of a single virus using the world's most powerful x-ray free-electron laser

Imaging the 3D structure of a single virus using the world's most powerful x-ray free-electron laser | Amazing Science | Scoop.it

By measuring a series of diffraction pattern from a virus injected into an XFEL beam, researchers at Stanford’s Linac Coherent Light Source (LCLS) have determined the first three-dimensional structure of a virus, using a mimivirus.


X-ray crystallography has solved the vast majority of the structures of proteins and other biomolecules. The success of the method relies on growing large crystals of the molecules, which isn’t possible for all molecules.


“Free-electron lasers provide femtosecond X-ray pulses with a peak brilliance ten billion times higher than any previously available X-ray source,” the researchers note in a paper inPhysical Review Letters. “Such a large jump in one physical quantity is very rare, and can have far reaching implications for several areas of science. It has been suggested that such pulses could outrun key damage processes and allow structure determination without the need for crystallization.”


The current resolution of the technique (about 100 nanometers) would be sufficient to image important pathogenic viruses like HIV, influenza and herpes, and further improvements may soon allow researchers to tackle the study of single proteins, the scientists say.


Mimivirus is one of the largest known viruses. The viral capsid is about 450 nanometers in diameter and is covered by a layer of thin fibres. A 3D structure of the viral capsid exists, but the 3D structure of the inside was previously unknown.

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Ultra-cold mirrors could reveal gravity's quantum side

Ultra-cold mirrors could reveal gravity's quantum side | Amazing Science | Scoop.it

An experiment not much bigger than a tabletop, using ultra-cold metal plates, could serve up a cosmic feast. It could give us a glimpse of quantum gravity and so lead to a "theory of everything": one that unites the laws of quantum mechanics, governing the very small, and those of general relativity, concerning the monstrously huge.


Such theories are difficult to test in the lab because they probe such extreme scales. But quantum effects have a way of showing up unexpectedly. In a strange quantum phenomenon known as the Casimir effect, two sheets of metal held very close together in a vacuum will attract each other.


The effect occurs because, even in empty space, there is an electromagnetic field that fluctuates slightly all the time. Placing two metal sheets very close to one another limits the fluctuations between them, because the sheets reflect electromagnetic waves. But elsewhere the fluctuations are unrestricted, and this pushes the plates together.

James Quach at the University of Tokyo suggests that we might be able to observe the equivalent effect for gravity. That would, in turn, be direct evidence of the quantum nature of gravity: the Casimir effect depends on vacuum fluctuations, which are only predicted by quantum physics.


But in order to detect it, you would need something that reflects gravitational waves – the ripples in space-time predicted by general relativity. Earlier research suggested that superconductors (for example, metals cooled to close to absolute zero such that they lose all electrical resistance) might act as mirrors in this way.


"The quantum properties of superconductors may reflect gravitational waves. If this is correct, then the gravitational Casimir effect for superconductors should be large," says Quach. "The experiment I propose is feasible with current technology."


It's still unclear if superconductors actually reflect gravitational waves, however. "The exciting part of this paper has to do with a speculative idea about gravitational waves and superconductors," says Dimitra Karabali at Lehman College in New York. "But if it's right, it's wonderful."

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The Search For Neutrons That Leak Into Our World From Other Universes

The Search For Neutrons That Leak Into Our World From Other Universes - The Physics arXiv Blog - Medium

"Braneworld" theories predict that matter can leak into and out of other universes. Thus, physicists are now actively searching for the first evidence of such events. These guys are proposing to measure this effect by placing a neutron detector close to a nuclear reactor to see whether neutrons appear unexpectedly as a result of being transported out of the reactor via another braneworld. Michael Sarrazin at the University of Namur in Belgium and a few pals say they have worked out to detect this leakage by measuring whether neutrons can bypass barriers by leaping into another brane and back again.


The theory is straightforward. Sarrazin and co say that braneworld theories predict that particles such as neutrons can exist in our brane and another at the same time, in a superposition of states. When these neutrons are disturbed by, say, a collision with a nuclei, the superposition is destroyed and the neutron ends up with a certain probability in one brane or the other. This is the process that allows neutrons to leak in and out of branes. An important goal of their experiment is to distinguish neutrons that have leaked into our universe from another brane from those that exist naturally in our universe. So much of Sarrazin and co’s work is determining how this can be done.


The conventional behaviour of neutrons is well understood. Physicists can calculate and measure the number of neutrons a nuclear reactor produces. Indeed, nuclear reactors are carefully shielded to stop these escapees. So the number of neutrons even relatively close to a shielded reactor should be small. But in addition to neutrons produced inside the reactor, there is always a background level of neutrons produced by cosmic ray collisions.


Sarrazin and co say they can distinguish these neutrons from the interlopers in three ways. To start with, their detector will be heavily shielded so neutrons cannot enter it from the outside. So any that are detected must have been created inside the detector.


The possibility for our visible world to be a 3-brane embedded in a multidimensional bulk is at the heart of many theoretical edifices in high energy physics. Probing the braneworld hypothesis is then a major experimental challenge. Following recent theoretical works showing that matter swapping can occur between braneworlds, we propose a "neutron-shining-through-a-wall" experiment. We first show that an intense neutron source such as a nuclear reactor core can induce a hidden neutron flux in an adjacent hidden braneworld. We then describe how a low background detector can detect neutrons arising from the hidden world and we quantify the expected sensitivity to the swapping probability. As a proof of concept, a constraint is derived from previous experiments.

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Exotic states of matter known as quantum spin Hall effect materialize with supercomputers

Exotic states of matter known as quantum spin Hall effect materialize with supercomputers | Amazing Science | Scoop.it
Scientists used supercomputers to find a new class of materials that possess an exotic state of matter known as the quantum spin Hall effect. The researchers published their results in the journal Science in December 2014, where they propose a new type of transistor made from these materials.


The science team included Ju Li, Liang Fu, Xiaofeng Qian, and Junwei Liu, experts in topological phases of matter and two-dimensional materials research at the Massachusetts Institute of Technology (MIT). They calculated the electronic structures of the materials using the Stampede and Lonestar supercomputers of the Texas Advanced Computing Center.


The computational allocation was made through XSEDE, the Extreme Science and Engineering Discovery Environment, a single virtual system funded by the National Science Foundation (NSF) that scientists use to interactively share computing resources, data and expertise. The study was funded by the U.S. Department of Energy and the NSF.


"To me, national computing resources like XSEDE, or specifically the Stampede and Lonestar supercomputers, are extremely helpful to computational scientists," Xiaofeng Qian said. In January 2015, Qian left MIT to join Texas A&M University as the first tenure-track assistant professor at its newly formed Department of Materials Science and Engineering.


What Qian and colleagues did was purely theoretical work, using Stampede for part of the calculations that modeled the interactions of atoms in the novel materials, two-dimensional transition metal dichalcogenides (TMDC). Qian used the molecular dynamics simulation software Vienna Ab initio Simulation Package to model a unit cell of atoms, the basic building block of the crystal lattice of TMDC.


The big picture for Qian and his colleagues is the hunt for new kinds of materials with extraordinarily useful properties. Their target is room-temperature quantum spin Hall insulators, which are basically near-two-dimensional materials that block current flow everywhere except along their edges. "Along the edges you have the so-called spin up electron flow in one direction, and at the same time you have spin down electrons and flows away in the opposite direction," Qian explained. "Basically, you can imagine, by controlling the injection of charge carriers, one can come up with spintronics, or electronics."


The scientists in this work proposed a topological field-effect transistor, made of sheets of hexagonal boron interlaced with sheets of TMDC. "We found a very convenient method to control the topological phase transition in these quantum spin Hall interlayers," Qian said. "This is very important because once we have this capability to control the phase transition, we can design some electronic devices that can be controlled easily through electrical fields."


Qian stressed that this work lays the theoretical ground for future real experiments in the lab. He hopes it might develop into an actual transistor suitable for a quantum computer, basically an as-yet-unrealized machine that manipulates data beyond just the binary of ones and zeros.


"So far, we haven't looked into the detailed applications for quantum computing yet," Qian said. "However, it is possible to combine these materials with superconductors and come up with the so-called Majorana fermion zero mode for quantum computing."

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CERN experiment brings precision to a cornerstone of particle physics

CERN experiment brings precision to a cornerstone of particle physics | Amazing Science | Scoop.it

 In a recent paper published in the journal Physical Review Letters, the COMPASS experiment at CERN reports a key measurement on the strong interaction. The strong interaction binds quarks into protons and neutrons, and protons and neutrons into the nuclei of all the elements from which matter is built. Inside those nuclei, particles called pions made up of a quark and an antiquark mediate the interaction. Strong interaction theory makes a precise prediction on the polarisability of pions – the degree to which their shape can be stretched. This polarisability has baffled scientists since the 1980s, when the first measurements appeared to be at odds with the theory. Today’s result is in close agreement with theory.


“The theory of the strong interaction is one of the cornerstones of our understanding of nature at the level of the fundamental particles,” said Fabienne Kunne and Andrea Bressan, spokespersons of the COMPASS experiment, “so this result, in perfect agreement with the theory, is a very important one.”


Despite the high energies available at CERN, the experiment is a big challenge, as the pion polarizability is tiny and its effect hard to isolate,” said Jan Friedrich, researcher at the Technische Universität München and leading scientist in the project.


Everything we see in the universe is made up of fundamental particles called quarks and leptons. Quarks are bound together in groups of three to make up the building blocks of the nuclei of elements – protons and neutrons. The hydrogen nucleus, for example, consists of a single proton, whereas the nucleus of a gold atom consists of 79 protons and 118 neutrons. Flitting between the protons and neutrons in a nucleus are pions, which mediate the strong force binding the nucleus together. These pions are made up of a quark and an antiquark, themselves held tightly bound by the strong force. This makes their deformability, or polarisability, a direct measure of the strong binding force between the quarks.


To measure the polarizability of the pion, the COMPASS experiment shot a beam of pions at a target of nickel. As the pions approached the nickel on average at distances twice the radius of the particles themselves, they experienced the very strong electric field of the nickel nucleus, which caused them to deform, and change trajectory, in the process emitting a particle of light called a photon. It is by measuring the photon energy and the deflection of the pion for a large sample of 63000 pions that the polarisability could be measured. The result reveals that the pion is significantly stiffer than shown by previous measurements, as expected from strong interaction theory.


“This result is admirably complementary to the studies of fundamental interactions performed at the LHC and a testimony to the diversity and strength of CERN’s research program,” said CERN Director General Rolf Heuer. “While the Higgs boson – proposed by Brout, Englert and Higgs – accounts for the masses of the fundamental particles, thereby allowing composite objects such as us to exist, the bulk of our mass comes from the binding energy of the strong interaction holding them together.”

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Technique greatly extends duration of fragile quantum states, pointing toward practical quantum computers

Technique greatly extends duration of fragile quantum states, pointing toward practical quantum computers | Amazing Science | Scoop.it

Quantum computers are experimental devices that promise exponential speedups on some computational problems. Where a bit in a classical computer can represent either a 0 or a 1, a quantum bit, or qubit, can represent 0 and 1 simultaneously, letting quantum computers explore multiple problem solutions in parallel. But such “superpositions” of quantum states are, in practice, difficult to maintain.


In a paper appearing this week in Nature Communications, MIT researchers and colleagues at Brookhaven National Laboratory and the synthetic-diamond company Element Six describe a new design that in experiments extended the superposition time of a promising type of qubit a hundredfold.


In the long term, the work could lead toward practical quantum computers. But in the shorter term, it could enable the indefinite extension of quantum-secured communication links, a commercial application of quantum information technology that currently has a range of less than 100 miles.


The researchers’ qubit design employs nitrogen atoms embedded in synthetic diamond. When nitrogen atoms happen to be situated next to gaps in the diamond’s crystal lattice, they produce “nitrogen vacancies,” which enable researchers to optically control the magnetic orientation, or “spin,” of individual electrons and atomic nuclei. Spin can be up, down, or a superposition of the two.


To date, the most successful demonstrations of quantum computing have involved atoms trapped in magnetic fields. But “holding an atom in vacuum is difficult, so there’s been a big effort to try to trap them in solids,” says Dirk Englund, the Jamieson Career Development Assistant Professor in Electrical Engineering and Computer Science at MIT and corresponding author on the new paper.


“In particular, you want a transparent solid, so you can send light in and out. Crystals are better than many other solids, like glass, in that their atoms are nice and regular and their electronic structure is well defined. And amongst all the crystals, diamond is a particularly good host for capturing an atom, because it turns out that the nuclei of diamond are mostly free of magnetic dipoles, which can cause noise on the electron spin.”

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Qubits as detectors show that space is not squeezed

Qubits as detectors show that space is not squeezed | Amazing Science | Scoop.it
Ever since Einstein proposed his special theory of relativity in 1905, physics and cosmology have been based on the assumption that space looks the same in all directions -- that it's not squeezed in one direction relative to another. A new experiment by physicists used partially entangled atoms -- identical to the qubits in a quantum computer -- to demonstrate more precisely than ever before that this is true: to one part in a billion billion.


The classic experiment that inspired Albert Einstein was performed in Cleveland by Albert Michelson and Edward Morley in 1887 and disproved the existence of an "ether" permeating space through which light was thought to move like a wave through water. What it also proved, said Hartmut Häffner, a UC Berkeley assistant professor of physics, is that space is isotropic and that light travels at the same speed up, down and sideways.


"Michelson and Morley proved that space is not squeezed," Häffner said. "This isotropy is fundamental to all physics, including the Standard Model of physics. If you take away isotropy, the whole Standard Model will collapse. That is why people are interested in testing this."


The Standard Model of particle physics describes how all fundamental particles interact, and requires that all particles and fields be invariant under Lorentz transformations, and in particular that they behave the same no matter what direction they move.


Häffner and his team conducted an experiment analogous to the Michelson-Morley experiment, but with electrons instead of photons of light. In a vacuum chamber he and his colleagues isolated two calcium ions, partially entangled them as in a quantum computer, and then monitored the electron energies in the ions as Earth rotated over 24 hours.


If space were squeezed in one or more directions, the energy of the electrons would change with a 12-hour period. It didn't, showing that space is in fact isotropic to one part in a billion billion (1018), 100 times better than previous experiments involving electrons, and five times better than experiments like Michelson and Morley's that used light.


The results disprove at least one theory that extends the Standard Model by assuming some anisotropy of space, he said.


Häffner and his colleagues, including former graduate student Thaned Pruttivarasin, now at the Quantum Metrology Laboratory in Saitama, Japan, will report their findings in the Jan. 29 issue of the journal Nature.

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Exotic, gigantic molecules - predicted since 1970 - fit inside each other like Russian nesting dolls

Exotic, gigantic molecules - predicted since 1970 - fit inside each other like Russian nesting dolls | Amazing Science | Scoop.it

University of Chicago scientists have experimentally observed for the first time a phenomenon in ultracold, three-atom molecules predicted by Russian theoretical physicist Vitaly Efimov in 1970.


In this quantum phenomenon, called geometric scaling, the triatomic molecules fit inside one another like an infinitely large set of Russian nesting dolls. “This is a new rule in chemistry that molecular sizes can follow a geometric series, like 1, 2, 4, 8…,” said Cheng Chin, professor in physics. “In our case, we find three molecular states in this sequence where one molecular state is about 5 times larger than the previous one.”

Chin and four members of his research group published their findings Dec. 9, 2014, in Physical Review Letters.


“Quantum theory makes the existence of these gigantic molecules inevitiable, provided proper—and quite challenging—conditions are created,” said Efimov, now at the University of Washington. The UChicago team observed three molecules in the series, consisting of one lithium atom and two cesium atoms in a vacuum chamber at the ultracold temperature of approximately 200 nanokelvin, a tiny fraction of a degree above absolute zero (minus 459.6 degrees Fahrenheit).


Given an infinitely large universe, the number of increasingly larger molecules in this cesium-lithium system also would extend to infinity. This remarkable idea stems from the exotic nature of quantum mechanics, which conforms to different laws of physics than those that govern the universe on a macroscopic scale.


“These are certainly exotic molecules,” said Shih-Kuang Tung, the postdoctoral scholar, now at Northwestern University, who led the project. Only under strict conditions could Tung and his colleagues see the geometric scaling in their Efimov molecules. It appears that neither two-atom nor four-atom molecules can achieve the Efimov state. “There’s a special case for three atoms,” Chin said.


Efimov’s reaction to the research was twofold: “First, I am amazed by the predictive power of the quantum theory,” he said. “Second, I am amazed by the skill of the experimentalists who managed to create those challenging conditions.”

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Information loss paradox may not exist: Black holes don’t erase information

Information loss paradox may not exist: Black holes don’t erase information | Amazing Science | Scoop.it

Shred a document, and you can piece it back together. Burn a book, and you could theoretically do the same. But send information into a black hole, and it’s lost forever. That’s what some physicists have argued for years: That black holes are the ultimate vaults, entities that suck in information and then evaporate without leaving behind any clues as to what they once contained. But new research shows that this perspective may not be correct.


“According to our work, information isn’t lost once it enters a black hole,” says Dejan Stojkovic, PhD, associate professor of physics at the University at Buffalo. “It doesn’t just disappear.” Stojkovic’s new study, “Radiation from a Collapsing Object is Manifestly Unitary,” appeared on March 17 in Physical Review Letters, with UB PhD student Anshul Saini as co-author. The paper outlines how interactions between particles emitted by a black hole can reveal information about what lies within, such as characteristics of the object that formed the black hole to begin with, and characteristics of the matter and energy drawn inside.


This is an important discovery, Stojkovic says, because even physicists who believed information was not lost in black holes have struggled to show, mathematically, how this happens. His new paper presents explicit calculations demonstrating how information is preserved, he says.


The research marks a significant step toward solving the “information loss paradox,” a problem that has plagued physics for almost 40 years, since Stephen Hawking first proposed that black holes could radiate energy and evaporate over time. This posed a huge problem for the field of physics because it meant that information inside a black hole could be permanently lost when the black hole disappeared — a violation of quantum mechanics, which states that information must be conserved.


In the 1970s, Hawking proposed that black holes were capable of radiating particles, and that the energy lost through this process would cause the black holes to shrink and eventually disappear. Hawking further concluded that the particles emitted by a black hole would provide no clues about what lay inside, meaning that any information held within a black hole would be completely lost once the entity evaporated.


Though Hawking later said he was wrong and that information could escape from black holes, the subject of whether and how it’s possible to recover information from a black hole has remained a topic of debate. Stojkovic and Saini’s new paper helps to clarify the story.

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Atomic Hong-Ou-Mandel Experiment: Helium atoms put in same quantum state, start appearing in same place

Atomic Hong-Ou-Mandel Experiment: Helium atoms put in same quantum state, start appearing in same place | Amazing Science | Scoop.it

Quantum mechanics has so many counterintuitive features that it seems possible to learn a new one every month. Today's lesson involves particles that are set into the same quantum state and effectively become indistinguishable. Once they are indistinguishable, they start behaving that way, showing up in the same place even when we'd expect to see them distributed at random. In today's issue of Nature, a paper describes getting atoms to behave this way, blurring the lines between a quantum probability function and what we think of as a physical object.


The original issue of indistinguishability was highlighted in an experiment done decades ago using photons. Called the Hong, Ou, and Mandel experiment, it involved sending photons in the same quantum state into a partial mirror along two different paths. The partial mirror, called a beam splitter, has a 50/50 chance of reflecting a photon, shifting it from one path to the second.


Based on the 50/50 chance, you'd expect three different outcomes. Half the time, when the beamsplitter reflects neither or both of the photons, you'd expect one photon in each of the output paths. When the beamsplitter reflects only one photon, you'd see both photons in one or the other path (with a 25 percent chance for each).


But quantum mechanics has also shown that things like electrons and heavier particles—even molecules—can behave as waves when given the chance. So a team from Universite Paris Sud decided to try to replicate the Hong, Ou, and Mandel experiment with something a bit more substantial than a photon. They chose 4-helium atoms, which are relatively easy to set in an identical quantum state.


The experiment involved holding the atoms over a sensor using an optical trap. Because of the way the trap was set up, the atoms would start off moving upward at two different velocities until the influence of gravity started pulling them back downward. While they were moving upward, the atoms were hit with photons that would exchange their momenta. This causes them to cross paths before they begin to fall. At the precise point where the paths cross, the atoms were hit with photons again. But this time, the photons were only half the intensity, leading to a 50/50 chance that their momenta would change. In essence, this acted like a beam splitter for atoms.


As a result, the atoms became indistinguishable—within the experiment, we'd have no idea of when we'd expect them to impact the detector. Our classically trained expectations would predict a Gaussian (bell) curve, with momenta distributed around the two starting speeds (7 and 12 cm/sec) due to random error and noise. And that's similar to what the results look like. Except if you look at the correlations between when particles land, you see the same sort of bias that Hong, Ou, and Mandel saw: the atoms seem to show up at one or the other of the two speeds, but not both. Since they were indistinguishable, they acted that way and travelled together.


The behavior isn't perfect—there are more atoms traveling along both paths than we'd expect if the experiment were operating perfectly. But the authors ascribe the difference to experimental noise, and the team notes this behavior is still radically different from what classical mechanics would predict. And having gotten this to work with atoms, it's possible the technique could be expanded to work with larger particles, allowing us to probe the boundaries between the quantum and classical worlds.

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Keith Wayne Brown's curator insight, April 3, 2015 11:28 AM

blurring the lines between probability and object

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Superconducting "Cooper pairs" of electrons have been split to create entangled pairs of electrons in a new device

Superconducting "Cooper pairs" of electrons have been split to create entangled pairs of electrons in a new device | Amazing Science | Scoop.it

Superconducting "Cooper pairs" of electrons have been split to create entangled pairs of electrons in a new device built by physicists in Finland and Russia. The device employs two quantum dots made of graphene. Although other types of quantum dots have been used for this purpose, the latest research suggests that graphene quantum dots should deliver long-lived entangled electron pairs that could be used in quantum computers.


Entanglement is a quantum-mechanical phenomenon in which properties of fundamental particles are correlated so that making a measurement on one particle can instantaneously affect another particle – even across very large distances. In principle, a quantum computer can use this connectedness to perform certain calculations much faster than a conventional computer. Although practical quantum computers do not exist today, some potential designs involve using the intrinsic angular momenta, or "spin", of electrons as quantum bits (qubits) of information that can be entangled.


Superconductors provide a ready source of entangled electrons because the Cooper pairs that allow these materials to conduct electricity with little or no resistance are in fact entangled pairs of electrons with opposite spin. Splitting the pairs while preserving the electrons' entanglement can be done simply by connecting ordinary metal wires to either end of the superconductor. If the set-up is just right, each wire will carry away one electron from a pair. However, it is more often the case that both electrons will end up going down the same wire.


One way to boost the odds in favour of separation is to replace the wires with tiny blobs of semiconductor containing just several thousand atoms. These quantum dots have electron energy levels that can be set precisely by carefully adjusting their size. The two electrons from each Cooper pair can be guided to different resonant energy levels and separated as a result. This approach has already been exploited using quantum dots made from indium arsenide and, with greater efficiency, using carbon nanotubes.


The latest work, carried out by Pertti Hakonen and colleagues at Aalto University in Finland together with Gordey Lesovik of the Landau Institute for Theoretical Physics near Moscow, instead uses quantum dots made from graphene. Graphene should be able to preserve the entanglement of the separated electron pair for longer, thanks to the fact that it consists of a single layer of carbon atoms, which constrains the electrons to move in a straight line and so avoids the emission of electromagnetic radiation that interferes with the spin state.


The team used electron-beam lithography to carve out two rectangular quantum dots (each 200 × 150 nm) from a layer of graphene deposited on a silicon-dioxide substrate. The dots were positioned 180 nm apart, covered by a superconductor made from a thin sandwich of titanium and aluminium, and connected to two metal contacts. To split the entangled electrons from the superconductor, the researchers first set the resonant energy level of the quantum dots to equal the energy possessed by the Cooper pairs. They then varied the gate voltage across one of the dots and monitored the current flowing through the other. They found that across most of the voltage range there was no current, but that at certain voltages the current would suddenly increase, drop below zero and then return to the zero mark. The rise, they explain, occurs because at that voltage the energy in one dot increases very slightly, while that in the other drops by the same small amount, causing the electrons to separate and so register a current (unseparated pairs register as zero current). The negative current, meanwhile, is caused by electrons "elastic co-tunnelling" through the superconductor. "It is like having a switch where you reverse the current by aligning the energy levels either symmetrically or antisymmetrically," says Hakonen.

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Bigger crashes promised: CERN’s Large Hadron Collider gears up for run 2

Bigger crashes promised: CERN’s Large Hadron Collider gears up for run 2 | Amazing Science | Scoop.it

Scientists will soon debut the blockbuster sequel to the so-called Big Bang Machine, which already found the elusive Higgs Boson. They're promising nearly twice the energy and far more violent particle crashes this time around. After a two-year shutdown and upgrade, the multi-billion dollar Large Hadron Collider is about to ramp up for its second three-year run. Scientists at the European Organization for Nuclear Research, or CERN, say if nature cooperates, the more powerful beam crashes will give them a peek into the unseen dark universe.


Beams should start running through the giant machine later this month, with the first high energy crashes probably coming in May, accelerator director Frederick Bordry said in a Thursday news conference in Geneva. A test beam ran through the collider last weekend, he said.


Scientists hope to see all sorts of new physics, including a first ever glimpse of dark matter, one of the chief focuses of the experiment.

"I want to see the first light in the dark universe," CERN General Director Rolf Heuer said. "If I see that, then nature is kind to me."


Dark matter — and its cousin, dark energy — make up most of the universe, yet scientists haven't been able to see them yet, so researchers are looking for them in high-energy crashes, in orbit on a special experiment on the international space station, and in a deep underground mine.


"What we know about dark matter is that it exists and then very little after that," MIT professor Michael Williams said at a science conference in February. CERN spent about $150 million to upgrade during its down time, opening the massive machine every 20 meters (66 feet), checking magnets, improving connections. "It's nearly a new machine," Heuer said. "It has the power which can melt 500 kilos (1100 pounds) of copper. Each beam. Two beams together, one ton of copper."

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Two quantum properties teleported together for first time

Two quantum properties teleported together for first time | Amazing Science | Scoop.it

The values of two inherent properties of one photon – its spin and its orbital angular momentum – have been transferred via quantum teleportation onto another photon for the first time by physicists in China. Previous experiments have managed to teleport a single property, but scaling that up to two properties proved to be a difficult task, which has only now been achieved. The team's work is a crucial step forward in improving our understanding of the fundamentals of quantum mechanics and the result could also play an important role in the development of quantum communications and quantum computers.


Quantum teleportation first appeared in the early 1990s after four researchers, including Charles Bennett of IBM in New York, developed a basic quantum teleportation protocol. To successfully teleport a quantum state, you must make a precise initial measurement of a system, transmit the measurement information to a receiving destination and then reconstruct a perfect copy of the original state. The "no-cloning" theorem of quantum mechanics dictates that it is impossible to make a perfect copy of a quantum particle. But researchers found a way around this via teleportation, which allows a flawless copy of a property of a particle to be made. This occurs thanks to what is ultimately a complete transfer (rather than an actual copy) of the property onto another particle such that the first particle loses all of the properties that are teleported.


Teleporting more than one state simultaneously is essential to fully describe a quantum particle and achieving this would be a tentative step towards teleporting something larger than a quantum particle, which could be very useful in the exchange of quantum information. Now, Chaoyang Lu and Jian-Wei Pan, along with colleagues at the University of Science and Technology of China in Hefei, have taken the first step in simultaneously teleporting multiple properties of a single photon.


In the experiment, the team teleports the composite quantum states of a single photon encoded in both its spin and OAM. To transfer the two properties requires not only an extra entangled set of particles (the quantum channel), but a "hyper-entangled" set – where the two particles are simultaneously entangled in both their spin and their OAM. The researchers shine a strong ultraviolet pulsed laser on three nonlinear crystals to generate three entangled pairs of photons – one pair is hyper-entangled and is used as the "quantum channel", a second entangled pair is used to carry out an intermediate "non-destructive" measurement, while the third pair is used to prepare the two-property state of a single photon that will eventually be teleported.

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Google collaborates with UCSB to build a quantum device that detects and corrects its own errors

Google collaborates with UCSB to build a quantum device that detects and corrects its own errors | Amazing Science | Scoop.it

Google launches an effort to build its own quantum computer that has the potential to change computing forever. Google is about to begin designing and building hardware for a quantum computer, a type of machine that can exploit quantum physics to solve problems that would take a conventional computer millions of years. Since 2009, Google has been working with controversial startup D-Wave Systems, which claims to make “the first commercial quantum computer.” Last year, Google purchased one of D-Wave’s machines to be able to test the machine thoroughly. But independent tests published earlier this year found no evidence that D-Wave’s computer uses quantum physics at all to solve problems more efficiently than a conventional machine.


Now, John Martinis, a professor at University of California, Santa Barbara, has joined Google to establish a new quantum hardware lab near the university. He will try to make his own versions of the kind of chip inside a D-Wave machine. Martinis has spent more than a decade working on a more proven approach to quantum computing, and built some of the largest, most error-free systems of qubits, the basic building blocks that encode information in a quantum computer.


“We would like to rethink the design and make the qubits in a different way,” says Martinis of his effort to improve on D-Wave’s hardware. “We think there’s an opportunity in the way we build our qubits to improve the machine.” Martinis has taken a joint position with Google and UCSB that will allow him to continue his own research at the university.


Quantum computers could be immensely faster than any existing computer at certain problems. That’s because qubits working together can use the quirks of quantum mechanics to quickly discard incorrect paths to a solution and home in on the correct one. However, qubits are tricky to operate because quantum states are so delicate.


Chris Monroe, a professor who leads a quantum computing lab at the University of Maryland, welcomed the news that one of the leading lights in the field was going to work on the question of whether designs like D-Wave’s can be useful. “I think this is a great development to have legitimate researchers give it a try,” he says.


Since showing off its first machine in 2007, D-Wave has irritated academic researchers by making claims for its computers without providing the evidence its critics say is needed to back them up. However, the company has attracted over $140 million in funding and sold several of its machines (see “The CIA and Jeff Bezos Bet on Quantum Computing”).


There is no question that D-Wave’s machine can perform certain calculations. And research published in 2011 showed that the machine’s chip harbors the right kind of quantum physics needed for quantum computing. But evidence is lacking that it uses that physics in the way needed to unlock the huge speedups promised by a quantum computer. It could be solving problems using only ordinary physics.


Martinis’s previous work has been focused on the conventional approach to quantum computing. He set a new milestone in the field this April, when his lab announced that it could operate five qubits together with relatively low error rates. Larger systems of such qubits could be configured to run just about any kind of algorithm depending on the problem at hand, much like a conventional computer. To be useful, a quantum computer would probably need to be built with tens of thousands of qubits or more.


Martinis was a coauthor on a paper published in Science earlier this year that took the most rigorous independent look at a D-Wave machine yet. It concluded that in the tests run on the computer, there was “no evidence of quantum speedup.” Without that, critics say, D-Wave is nothing more than an overhyped, and rather weird, conventional computer. The company counters that the tests of its machine involved the wrong kind of problems to demonstrate its benefits.


Martinis’s work on D-Wave’s machine led him into talks with Google, and to his new position. Theory and simulation suggest that it might be possible for annealers to deliver quantum speedups, and he considers it an open question. “There’s some really interesting science that people are trying to figure out,” he says.

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Benjamin Chiong's curator insight, March 23, 2015 7:23 PM

Looking at Amdahl's law, it is not only the data storage that matters but every component of computer. As each piece of hardware advances, the rest of the parts should be able to keep up as well. Quantum Computing forges a world that allows massive processing power to analyze Big Data. This gives us an idea how the future would look like.

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Light simultaneously imaged as a wave and a particle for the first time

Light simultaneously imaged as a wave and a particle for the first time | Amazing Science | Scoop.it

For the first time ever, scientists have photographed light behaving simultaneously as both a particle and a wave. The image is a momentous achievement, providing direct observation of both behaviors simultaneously for the first time, after decades of attempts by the scientific community. Previous research projects have successfully observed wave-like behaviors and particle-like behaviors in light, but not at the same time.


The dual behavior of light, which is demonstrated through quantum mechanics and was first proposed by Albert Einstein, was only possible to capture by scientists at École Polytechnique Fédérale de Lausanne (EPFL), Switzerland, due to an unorthodox imaging technique. The scientists generated the image with electrons, making use of EPFL’s ultrafast energy-filtered transmission electron microscope. This gave them a rare advantage over other institutions, as EPFL has one of only two microscopes in the world.


The image was achieved first by firing a pulse of laser light at a miniscule metallic nanowire, adding energy to charged particles in the nanowire and making them vibrate. The light waves  travel along the nanowire in opposite directions, like lanes of cars on a road, but when they meet from opposite directions they form a new wave the appears as if it is “standing in place”, effectively confined to the nanowire. This wave, which radiates around the nanowire, was the light source that was imaged.


The scientists fired a stream of electrons in close proximity to the nanowire, and imaged their interaction with this “standing wave”. As they came into contact with the light, their changes in behavior acted as a visualization of the light’s behavior. The electrons that interacted with the light, or photons, either slowed down or sped up, together forming a visualization of the light’s wave. However, the changes in speed also appeared as an exchange of quanta – packets of energy – between the electrons and the photons.  These packets were the tell-tale sign of the light behaving as a particle.

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Quantum Physics Can Fight Fraud By Making Credit Card Verification Unspoofable

Quantum Physics Can Fight Fraud By Making Credit Card Verification Unspoofable | Amazing Science | Scoop.it

Decades of data security research have brought us highly reliable, standardized tools for common tasks such as digital signatures and encryption. But hackers are constantly working to crack data security innovations. Current credit/debit card technologies put personal money at risk because they’re vulnerable to fraud.


Physical security – which deals with anti-counterfeiting and the authentication of actual objects – is part of the problem too. The good guys and bad guys are locked in a never-ending arms race: one side develops objects and structures that are difficult to copy; the other side tries to copy them, and often succeeds.


But we think our new invention has the potential to leave the hackers behind. This innovative security measure uses the quantum properties of light to achieve fraud-proof authentication of objects.


The arms race is fought in secret; revealing your technology helps the enemy. Consequently, nobody knows how secure a technology really is. Remarkably, a recent development called Physical Unclonable Functions (PUFs) has made it possible to be completely open. A PUF is a piece of material that can be probed in many ways and that produces a complex response that depends very precisely on the challenge and the PUF’s internal structure.


The best known examples are Optical PUFs. The PUF is a piece of material – such as white paint with millions of nanoparticles – that will strongly scatter any light beamed at it. The light bounces around inside the paint, creating a unique pattern that can be used for authentication. Optical PUFs could be used on any object, but would be especially useful on credit/debit cards.


In 2012, researchers at Twente University realized they discovered something very important. The magic ingredient is a Spatial Light Modulator (SLM), a programmable device that re-shapes the speckle pattern. In their experiments, they programmed an SLM such that the correct response from an Optical PUF gets concentrated and passes through a pinhole, where a photon detector notices the presence of the photon. An incorrect response, however, is transformed to a random speckle pattern that does not pass through the pinhole. The method was dubbed Quantum-Secure Authentication (QSA).


QSA does not require any secrets, so no money has to be spent on protecting them. QSA can be implemented with relatively simple technology that is already available. The PUF can be as simple as a layer of paint. It turns out that the challenge does not have to be a single photon; a weak laser pulse suffices, as long as the number of photons in the pulse is small enough. Laser diodes, as found in CD players, are widely available and cheap. SLMs are already present in modern projectors. A sensitive photodiode or image sensor can serve as the photon detector. With all these advantages, QSA has the potential to massively improve the security of cards and other physical credentials.

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Two new baryons - found at CERN - made of three quarks each are a new exotic twist of normal protons and neutrons

Two new baryons - found at CERN - made of three quarks each are a new exotic twist of normal protons and neutrons | Amazing Science | Scoop.it

Two new particles made of exotic types of quarks have appeared inside the Large Hadron Collider (LHC) near Geneva, Switzerland. The particles are never-before-seen species of baryons—a category of particles that also includes the familiar protons and neutrons inside atoms. The new baryons had been long predicted to exist, but their specific characteristics, such as their mass, were unknown until they were discovered in the flesh. The new measurements serve to confirm and refine the existing theory of subatomic particles and help pave the way for a deeper theory that could include even more exotic particles.
 
Scientists at the collider’s Large Hadron Collider beauty (LHCb) experiment reported the discovery of the baryons, called Xib'and Xib*(pronounced “zi-b-prime” and “zi-b-star”), February 10, 2015,  in Physical Review Letters. (They posted a preprint of their paper in November on the arXiv server.) “These were two things that very much should have existed,” says Matthew Charles of Paris 6 University Pierre and Marie Curie, a co-author of the study. “Of course, you still have to check because every now and then you get a surprise.” Both particles contain one beauty, or b, quark, one strange quark and one down quark. What differentiates these particles from one another, and from one other conglomeration of the same three types of quarks that was previously found at the LHC, is the arrangement of the quarks' spins.


Spin is one of the basic quantum characteristics intrinsic to any particle, and comes in unitless, discrete amounts. All quarks have a spin of one half. When two quarks inside the same particle are spinning in the same direction, their spins add together; when they rotate in opposite directions their spins cancel out. Spins are like magnets in that like repels like, so quarks prefer to spin in opposite directions. Extra energy is needed to align two quarks to spin in the same direction. The lowest-energy configuration of a Xib particle is for the two lightest quarks (the down and strange) to be antialigned, with their spins canceling out to zero, and the heavy b quark spinning in either direction, adding another one-half spin for a total spin of one half. That ground state, called Xib*0, was found at the LHC in 2012.
 
The two newfound baryons are higher-energy configurations. Both have the lightest two quarks spinning in parallel, adding to a combined spin of 1. Xib'has its b quark spinning opposite those two, giving the particle a total spin of one half (from 1 minus one-half). In Xib* the spin of all three quarks is aligned, giving it a total spin of 1 and a half. This triple alignment requires the most energy of any configuration, causing Xib* to be the heaviest of the three states.
 
Before the particles were discovered, physicists had estimated their masses based on a theory called quantum chromodynamics (QCD), which describes the strong force—one of the four fundamental forces of nature—that is responsible for binding quarks together. The strong force is carried by particles called gluons, so inside any particle held together by the strong force there will also be gluons. And in addition to the main quarks and gluons “virtual” pairs of quarks and antiquarks (the antimatter counterpart of quarks) continuously pop into and out of existence. This particle zoo makes calculations based on QCD incredibly difficult, to the point that mass estimates can only be accomplished using powerful supercomputers running complex simulations that aim to take all of the constituents of the particle into account. “We supposedly have a theory that tells us how these particles are supposed to behave and in principle it should open new doors. But in practice, our ability to calculate is quite limited,” says Frank Wilczek, a theoretical physicist at the Massachusetts Institute of Technology who won the Nobel Prize for helping to formulate QCD.

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Scientists slow down the speed of light traveling through air

Scientists slow down the speed of light traveling through air | Amazing Science | Scoop.it

Scientists have long known that the speed of light can be slowed slightly as it travels through materials such as water or glass. However, it has generally been thought impossible for particles of light, known as photons, to be slowed as they travel through free space, unimpeded by interactions with any materials.


In a new paper published in Science Express  on January 23, 2015, researchers from the University of Glasgow and Heriot-Watt University describe how they have managed to slow photons in free space for the first time. They have demonstrated that applying a mask to an optical beam to give photons a spatial structure can reduce their speed. Their experiment was configured like a race, with two photons released simultaneously across identical distances towards a defined finish line.


The team compare a beam of light, containing many photons, to a team of cyclists who share the work by taking it in turns to cycle at the front. Although the group travels along the road as a unit, the speed of individual cyclists can vary as they swap position. The group formation can make it difficult to define a single velocity for all cyclists, and the same applies to light. A single pulse of light contains many photons, and scientists know that light pulses are characterized by a number of different velocities.


The researchers found that one photon reached the finish line as predicted, but the structured photon which had been reshaped by the mask arrived later, meaning it was traveling more slowly in free space. Over a distance of one meter, the team measured a slowing of up to 20 wavelengths, many times greater than the measurement precision.


The work demonstrates that, after passing the light beam through a mask, photons move more slowly through space. Crucially, this is  very different to the slowing effect of passing light through a medium such as glass or water, where the light is only slowed during the time it is passing through the material – it returns to the speed of light after it comes out the other side. The effect of passing the light through the mask is to limit the top speed at which the photons can travel.


Daniel Giovannini, one of the lead authors of the paper, said: “The delay we’ve introduced to the structured beam is small, measured at several micrometers over a propagation distance of one meter, but it is significant. We’ve measured similar effects in two different types of beams known as Bessel beams and Gaussian beams.” Co-lead author Jacquiline Romero said: “We’ve achieved this slowing effect with some subtle but widely-known optical principles. This finding shows unambiguously that the propagation of light can be slowed below the commonly accepted figure of 299,792,458 metres per second, even when travelling in air or vacuum. 

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Self-propelled subatomic particles accelerate without a push, extending lifetime of unstable isotopes

Self-propelled subatomic particles accelerate without a push, extending lifetime of unstable isotopes | Amazing Science | Scoop.it

Some physical principles have been considered immutable since the time of Isaac Newton: Light always travels in straight lines. No physical object can change its speed unless some outside force acts on it.


Not so fast, says a new generation of physicists: While the underlying physical laws haven’t changed, new ways of “tricking” those laws to permit seemingly impossible actions have begun to appear. For example, work that began in 2007 proved that under special conditions, light could be made to move along a curved trajectory — a finding that is already beginning to find some practical applications.


Now, in a new variation on the methods used to bend light, physicists at MIT and Israel’s Technion have found that subatomic particles can be induced to speed up all by themselves, almost to the speed of light, without the application of any external forces. The same underlying principle could also be used to extend the lifetime of some unstable isotopes, perhaps opening up new avenues of research in basic particle physics.


The findings, based on a theoretical analysis, were published in the journal Nature Physics by MIT postdoc Ido Kaminer and four colleagues at the Technion. The new findings are based on a novel set of solutions for a set of basic quantum-physics principles called the Dirac equations; these describe the relativistic behavior of fundamental particles, such as electrons, in terms of a wave structure. (In quantum mechanics, waves and particles are considered to be two aspects of the same physical phenomena). By manipulating the wave structure, the team found, it should be possible to cause electrons to behave in unusual and counterintuitive ways.

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Laser may replace copper in computer chips for high-speed, low-energy data transmission

Laser may replace copper in computer chips for high-speed, low-energy data transmission | Amazing Science | Scoop.it

An international team of scientists has constructed the first germanium-tin* semiconductor laser for CMOS silicon chips. By replacing copper wires with optical transmission, the new device promises higher-speed data transmission on computer chips at a fraction of the energy.

The results by scientists from Forschungszentrum Jülich and the Paul Scherrer Institute in Switzerland in cooperation with international partners were published in the journal Nature Photonics.


Transferring data between multiple cores and between logic elements and memory cells is a key bottleneck in fast-developing computer technology. “Signal transmission via copper wires limits the development of larger and faster computers due to the thermal load and the limited bandwidth of copper wires,” explains Prof. Detlev Grützmacher, Director at the Forschungszentrum Jülich Peter Grünberg Institute. “The clock signal alone uses up to 30% of the energy, which can be saved through optical transmission.”


The more than 10% tin content is what enables the new germanium-tin semiconductor optical properties, according to the scientists. The laser is currently limited to low temperatures of up to minus 183 degrees Celsius in the test system. The next big step will be generating laser light with electricity, and without the need for cooling, if possible. The aim is to create an electrically pumped laser that functions at room temperature.


*The basis of chip manufacturing is silicon, an element of main group IV of the periodic table. Typical semiconductor lasers for telecommunication systems, made of gallium arsenide for example, however, are costly and consist of elements from main groups III or V. This has profound consequences on the crystal properties. Such laser components cannot therefore be applied directly onto silicon. They have to be produced externally at great effort and subsequently glued to the silicon wafer. However, the lifetime of this kind of component is greatly reduced due to the fact that the thermal expansion coefficients of these elements are significantly different from that of silicon. In contrast, semiconductors of main group IV — to which both silicon and germanium belong — can be integrated into the manufacturing process without any major difficulties. Neither element by itself is very efficient as a light source, however. They are classed among the indirect semiconductors. In contrast to direct semiconductors, they emit mostly heat and only a little light when excited.

The scientists at Jülich’s Peter Grünberg Institute have now for the first time succeeded in creating a “real” direct main group IV semiconductor laser by combining germanium and tin, which is also classed in main group IV.

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