Recently in Quantum physics and information Category

Gizmag: With the rising popularity of "cloud computing"—the sharing of resources, software, and information over the internet—security is a growing concern. To preserve privacy while users interact with remote computing centers, researchers in Austria have combined quantum computing with quantum cryptography in a process called blind quantum computation. According to Stefanie Barz and colleagues, whose paper was published online in Science on 20 January, users prepare qubits in a state known only to themselves. They send the qubits to a quantum computer, which entangles and then manipulates them to execute a particular computation, whose results are sent back to the users. The users' input, output, and algorithms are never disclosed to the company doing the computations, and no eavesdropper can read the qubits without knowing their initial state. The researchers emphasize, however, that their experiment is only one step toward unconditionally secure quantum computing.

Nature: New research indicates that not everything on a quantum level exhibits quantum behavior. Wires just a few nanometers wide have now been shown to conduct electricity in the same way as the larger components of existing devices. Michelle Simmons, a physicist and director of the Centre for Quantum Computation and Communication Technology at the University of New South Wales in Sydney, Australia, and her colleagues made atomic-scale wires of phosphorous-doped silicon in which the phosphorous provided the extra electrons needed to generate a current, writes Edwin Cartlidge for Nature. Although the width of the wires varied from 1.5 to 11 nm, the resistivity did not differ substantially, thus obeying Ohm’s law of classical electronics. David Ferry, an electrical engineer at Arizona State University in Tempe, noted the importance of the finding to such devices as transistors, which every two years have been shrinking in size yet yielding ever-better performance—a trend known as Moore’s law. If quantum coherence came into play, he said, the transistors wouldn’t turn on and off as expected. Therefore, the new research could have significant implications for the microchip industry. What the implications will be for quantum computing, however, remains to be seen.

Science: Researchers at the US National Renewable Energy Laboratory (NREL) have created a new type of solar cell that captures some of the excess solar energy normally lost as heat, writes Robert Service for Science. When high-energy photons from the Sun hit a semiconducting material in a solar cell, they excite the semiconductor’s electrons from a static position so they can conduct. But the photons carry more energy than is needed, and the rest gets lost as heat. Several years ago, it was found that the high-energy photons can excite more than one electron if the semiconductor consists of nanometer-sized particles called quantum dots. The NREL group used the process, known as multiple exciton generation (MEG), in their quantum dot solar cell to achieve a 5% overall efficiency at converting light to electricity. That efficiency is still well below conventional silicon solar cells, which make better use of the full solar spectrum. But the device is the first to collect more electrical charges than the number of photons that struck the quantum dots—a convincing demonstration of MEG. The group’s results were published 16 December.

Science: Quantum tunneling is a phenomenon in which a particle tunnels through a barrier that it could not, according to the laws of classical mechanics, surmount. It has already been demonstrated in semiconductors in which electrons tunnel through nonconducting layers of material. Mika Sillanpää of Aalto University in Finland and colleagues think that much larger objects can be made to behave similarly. They designed an experiment in which a micrometer-wide membrane made of graphene is suspended over a metal plate. With electrical voltage applied, the membrane would have two stable positions: bowed slightly in the middle, or bent enough to be in contact with the metal plate underneath. The combined electrical and mechanical forces on the membrane would create an energy barrier between the two positions. At temperatures of less than 1 millikelvin, the membrane could only move from one stable position to the other by quantum tunneling. Sillanpää says achieving the necessary low temperatures may take several years, but he and his team are moving forward with an experiment.

National Post: Random number sequences are usually generated by computational algorithms, which only give the appearance of randomness, but a new technique uses a laser light pulse to create truly random numbers. Ben Sussman of Canada’s National Research Council and coworkers have found that when they shine a pulse of laser light at a diamond, the light changes as it passes through because it interacts with quantum vacuum fluctuations. What happens to the light is unknown and, fundamentally, unknowable. The measurements of the pulses of light that emerge from the diamond are therefore random in a way that nothing in our ordinary surroundings is, writes Tom Spears for Canada’s National Post. “A truly random number generator will provide impenetrable encryption for communications—be they military transmissions, secure banking, or online purchasing—that underpin the modern connected world,” said Sussman.

Nature: With the use of lasers, hackers have now found a way to fake the quantum property of entanglement at the heart of cryptographic systems, reports Nature's Zeeya Merali. Entanglement here refers to the relationship between two photons that are connected in such a way that measuring the polarization state of one instantaneously modifies the polarization state of its partner. Each of the two entangled photons is assigned to an entity, say Alice and Bob. Any attempt by a third party to eavesdrop by intercepting either Alice’s or Bob's photon will destroy the entanglement. To check the entanglement is secure a technique called the Bell test is used..

Christian Kurtsiefer of the National University of Singapore and colleagues, however, discovered one can cheat the Bell test by blinding Bob's detectors with a laser beam and intercepting its photons. While blinded, the detector can be tricked into registering the correct value whenever the hacker fires an additional laser pulse at it.

The theoretical version of the Bell test would pick up on this deception, but in the real world, the equipment compensates for inperfections and hence treats the signal as valid.

New Scientist: Researchers at the University of Cambridge have succeeded in capturing single electrons and moving them back and forth between two electrical traps. Such quantum manipulation represents a milestone in the area of quantum computing. Quantum computers send information in the form of single particles, called quantum bits, or qubits. However, those qubits are notoriously fragile—just trying to measure them can destroy them. So the researchers had to develop a method to transfer the qubits from the area where they perform the calculations to a separate spot where the qubits can be measured in isolation. Using a surface acoustic wave, Crispin Barnes and colleagues were able to bounce a single electron between two quantum dots connected via a long channel. Their results appear today in Nature.

Cosmos: "'Squeezing' laser light could significantly improve the accuracy of detectors searching for Einstein's elusive gravitational waves," writes Myles Gough for Cosmos magazine. Because gravitational waves, which are generated by violent astronomical events, have traveled billions of light-years before reaching Earth, they are greatly weakened and thus difficult to detect. Until now, the accuracy of the laser interferometers used to detect the waves has been limited by a quantum phenomenon of light called "shot noise"—a type of electronic interference. To overcome this problem, Roman Schnabel of the Max Planck Institute for Gravitational Physics in Germany and coworkers perfected a method of "squeezing" the light to reduce the noise to less than that dictated by the Heisenberg uncertainty principle and then feeding the squeezed light into the interferometer, along with the normal laser light, which resulted in a laser beam with a much more uniform intensity. "One can say that for the first time a 'technology' is based on one of the distinct features of quantum physics itself. We were able to leave the stage of laboratory experiments and realize a real application," said Schnabel. The group's results, published in Nature Physics, are an exciting step forward for the Laser Interferometry Gravitational-Wave Observatory (LIGO) project in its quest to observe gravitational waves using Earth-based detectors.

Nature: Last month's "excess events" at the Large Hadron Collider (LHC) were probably just statistical fluctuation, rather than hints of the Higgs boson, according to new data. The events appeared as an excess of W bosons at around 144 gigaelectronvolts (GeV) in the ATLAS and Compact Muon Solenoid detectors; higher-than-expected numbers of W bosons were predicted to be an early indicator of the Higgs. Presented today at the Lepton Photon 2011 conference in Mumbai, India, the new results, which use about twice the data, show the significance of the find dropping from 2.8 sigma to 2 sigma, which means that the odds of it being the real Higgs have fallen, from more than 99% to 95%—the opposite of what one would hope with additional data. While teams at the LHC can't yet say where the Higgs is, the CMS experiment ruled out its presence at energies between 145 and 400 GeV, while the ATLAS has eliminated large patches between 146 and 466 GeV. If the Higgs exists, it may be at the lower mass end of the energy spectrum, between about 120 and 140 GeV.

New Scientist: Can large objects follow quantum laws? To answer that question, Oriol Romero-Isart from the Max Planck Institute of Quantum Optics in Garching, Germany, and colleagues are experimenting to see whether a nanometer-sized glass sphere can exist in two entirely distinct places at one time, with no overlap. They propose placing the sphere in a small cavity and striking it with a laser, causing it to bounce around in the cavity. But since the light is quantum in nature, writes Michael Brooks for New Scientist, so too will be the position of the sphere, which forces the sphere into a quantum superposition. So far, such superposition has only been achieved with molecules containing a few hundred atoms. Romero-Isart is lead author on the group’s paper published 8 July in Physical Review Letters.

Nature: One of the most important tenets of quantum mechanics, writes Geoff Brumfiel for Nature, is the principle that empty space is not empty at all. Vacuum contains particles coming in and out of existence, some so quickly that they're described as virtual. They can have tangible effects regardless of the brevity of their presence.

Theoretically, a mirror moving through a vacuum at nearly the speed of light can convert virtual photons into observable real photons. Per Delsing of Chalmers University of Technology in Sweden and colleagues used a piece of quantum electronics known as a superconducting quantum interference device (SQUID) to make a superconducting circuit in which the SQUID acted as a mirror.

When they passed a magnetic field through the SQUID, it moved slightly, and when they switched the direction of the magnetic field back and forth several billion times a second, the SQUID moved back and forth in response, at about 5% the speed of light, and produced a shower of observable microwave photons. If the findings are verified, they would be one of the most unusual experimental proofs of quantum mechanics in recent years.

Nature: Quantum effects are usually detected indirectly via precision instruments. Now Nicolas Gisin, of the University of Geneva in Switzerland, and colleagues have created a new test to see if the human eye can pick up signs of entanglement, writes Zeeya Merali for Nature. The researchers entangled two photons, sent one to a standard photon detector, and amplified the other, creating a light field of thousands of photons with the same quantum state. The humans in the experiment observed the same effects of entanglement that the photon detectors recorded. However, Gisin set up the experiment so that the state of the second, amplified photon was measured before amplification, thus breaking the entanglement. Both the human observers and the photon detectors were deceived into giving false positives by the effect known as the detection loophole: Some photons will always be lost during the experiment. The more photons involved, the more the effect is magnified—and the more the results for both human and mechanical detectors are distorted.

Ars Technica: The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory has produced the heaviest antimatter particle ever seen in a laboratory: antihelium-4, the antimatter partner of the alpha particle. Antihelium-3 was detected in the 1970s, but the antialpha has proved more difficult to spot. For a nucleus to condense, the right number of antimatter baryons of the right types must be traveling near enough to one another, with similar enough momenta. By colliding gold atoms, which each have 79 protons and 118 neutrons, RHIC increased the chances that antialphas would form. The discovery, published in Nature, will inform the search for antimatter elsewhere, including on the International Space Station. On 29 April the space shuttle Endeavour will begin a journey to the station to drop off the Alpha Magnetic Spectrometer, which will look for primordial antimatter.

Daily Mail: Scientists at the University of Tokyo have found a way to teleport photons from one place to another. A team led by Noriyuki Lee used the quantum entanglement characteristic—where two particles can affect each other even after being separated—to dismantle a photon and then reassemble it elsewhere. According to livescience.com, the team linked a photon to one half of a pair of entangled particles, and then destroyed the photon and the particle it had been linked to. But because the remaining particle of the formerly entangled pair maintains a link to its partner—which had been linked with the photon—the photon can be reassembled elsewhere. Although a far cry from the teleportation machine in Star Trek, the technology may be one small step on the road to teleporting larger objects. On Friday Lee and coworkers published their results in Science, and physicist Philippe Grangier of France’s Institut d’Optique published an accompanying essay on the research.

BBC: Data from Fermilab's Tevatron particle accelerator, which could indicate a never-before-seen particle, may signal the most radical change in physics that has occurred in decades. Data from the collisions between protons and anti-protons yielded an unexpected "bump" that did not indicate the presence of the much-sought-after Higgs boson but rather something that the standard model does not include. The result is at the three-sigma level of certainty—there is about a one in a thousand chance that it is due to a statistical fluctuation and nothing more. Formal discoveries require a five-sigma level of certainty—a one in a million chance that the result is a statistical fluke. The possibility also exists that the result was caused by mismodelng of the background. Researchers have at least twice as much data as are contained in the first analysis, and they are working through the data to find out if their initial understanding was correct. If so, they may have discovered a fifth fundamental force of nature.

New Scientist: A researcher at the University of Tours in France has proposed that the vacuum of space could be turned into a superconductor. Maxim Chernodub’s proposal is a consequence of the uncertainty principle of quantum theory, which states that one can never be sure that a vacuum is truly empty. “Instead, space is fizzing with ‘virtual’ particles, which tend to disappear almost as soon as they form,” writes Maggie McKee for New Scientist. Exposing those charged particles to a strong magnetic field causes their internal magnetic field to align with the external one; if the field is strong enough, the virtual particles can become real. Such particles all share the same quantum state and form what is known as a Bose–Einstein condensate, in which they flow together as one and carry current without resistance. Chernodub’s work is due to be published in Physical Review Letters.

BBC: The controversial idea that our sense of smell may have its basis in quantum events is gaining traction, writes Jason Palmer for BBC News. Andrew Horsfield at Imperial College London and colleagues, presenting at this month's American Physical Society meeting in Dallas, Texas, say that quanta lost by electrons are the key to the process. Luca Turin of MIT recently published a paper showing that flies can distinguish molecules containing a heavier version of hydrogen from other, chemically similar molecules. Like a spring with a heavier weight at one end, the vibration frequency is lowered, and flies appear to notice. "All sorts of interesting biological physics that implements quantum processes" is cropping up, said Jennifer Brookes, also at MIT. "I believe it's time for the idea to develop and for us to get on with testing it."

Science News: A new way to manipulate atoms inside diamond crystals so that they store information long enough to function as quantum memory is being developed, writes Devin Powell for Science News. But the scientists involved aren’t looking for perfect diamonds, rather for ones with defects. One of the most common defects in diamond is nitrogen, which turns the stone yellow. When a nitrogen atom sits next to a vacant spot in the carbon crystal, the intruding element provides an extra electron that moves into the hole. Several years ago, scientists learned how to change the spin of such electrons using microwave energy and put them to work as quantum bits, or qubits. Diamond memory has several advantages: It works at room temperature, it’s very stable, and it can be scaled up to larger sizes. David Awschalom of the University of California, Santa Barbara, discussed the technique at the American Physical Society’s March meeting in Dallas, Texas.

Chronicle of Higher Education: This year's TED conference winds down today in Long Beach, California. Short for Technology, Entertainment, Design, TED features short talks by eloquent, engaging experts from diverse fields, including the physical sciences. As the Chronicle's Jeffrey Young explains, TED is unlike the kind of conferences that academics usually attend. Talks are just 18 minutes long, lack question-and-answer sessions at the end, and are professionally videoed and posted on the Web. Among the speakers at this year's event is Aaron O'Connell, who is part of the team that succeeded in nudging a tiny cantilever in and out of its quantum ground state.

Nature: The latest results from the Large Hadron Collider in Switzerland are casting doubt on the theory of supersymmetry (SUSY), which was developed to help resolve problems with the standard model of particle physics, writes Geoff Brumfiel for Nature. Colliders have failed to turn up direct evidence of the superparticles predicted by the theory, such as supersymmetrical quarks or the Higgs boson. Theorists can still make SUSY work, but only by assuming very specific masses for the superparticles—the kind of fine-tuning exercise that the theory was invented to avoid. If SUSY is not discovered, theoretical physicists will have to go back to the drawing board and find an alternative way to solve the problems with the standard model.

New York Times: In an elegant melding of theoretical and experimental physics, scientists at Yale University have taken the basic function of a laser and flipped it around—producing a device that absorbs, rather than emits, a beam of light, writes Henry Fountain for the New York Times. The device, which the scientists call a “coherent perfect absorber” or, more popularly, an anti-laser, may lead to the development of new kinds of switches, filters, and other components that could be useful in hybrid optical-electronic computers under development, among other applications. A. Douglas Stone, a theoretical physicist at Yale, and colleagues published their results last week in Science.

Scientific Computing: Inspired by the popular confidence trick known as the "shell game," researchers at the University of California, Santa Barbara, have demonstrated the ability to hide and shuffle "quantum-mechanical peas"—in the form of microwave single photons—under and between three microwave resonators, or "quantized shells." In a paper published in Nature Physics, UCSB researchers show the first demonstration of the coherent control of a multi-resonator architecture. That feat has been a holy grail among physicists studying photons at the quantum-mechanical level for more than a decade.

MSNBC: Physicists from Canada’s TRIUMF particle-physics facility, the University of British Columbia, and Brookhaven National Laboratory have theorized a particle that can explain both dark matter and the origins of matter and antimatter—the “X” particle. In their paper published last month in Physical Review Letters, the team explains that the yet-to-be-discovered X particle is expected to decay mostly to normal matter, whereas its antiparticle is expected decay mostly to "hidden" antimatter. The team claims that its existence in the early universe could explain why there is more matter than antimatter in the universe—and that dark matter is in fact hidden antimatter, as explained by Kate McAlpine writing for Physics World.

Science: A planned €500 million particle collider to be built outside Rome is moving forward as Italy increases its investment and other groups jump on board. The SuperB project, which will be built from parts of a decommissioned US accelerator, would generate large quantities of B mesons to study charge conjugation–parity (CP) violation—the asymmetry between matter and antimatter. The project faces competition from the Japanese, however, who are working to build the Super KEKB, which would pursue much the same research.

Nature: Solid-state quantum computing moved a step closer to being realized as two research groups report their progress on entangling qubits—or quantum bits—made from superconducting circuits. The groups have achieved three-qubit entanglement, the minimum number needed for quantum error correction. Eugenie Samuel Reich tackles the technical details in her Nature article.

Nature: In theory, sending quantum-encrypted messages is secure because any attempt at snooping is apparent to the recipient. In practice, the physical systems that encrypt the messages are imperfect. Noise creeps in. Still, until now, physicists had believed that if noise remained below 20%, snooping would be exposed. The University of Toronto's Feihu Xu, Bing Qi, and Hoi-Kwong Lo have devised a method to intercept quantum encrypted communication while remaining below the 20% detection threshold.

physicsworld.com: A war of words has broken out in the dark-matter community over a report posted on the arXiv e-print server earlier this week. The preprint from the XENON100 collaboration poured cold water on claims that dark matter has been detected by two other experiments—but now the report itself has been attacked by other researchers in the field.

New Scientist: Corrected: 5/6/2010: The tetraquark, a massive particle made up of four quarks, may have been seen at KEK particle accelerator in Tsukuba, Japan.

Thirty years ago, tetraquarks were proposed as a solution to the equations of quantum chromodynamics. QCD is a theory developed to describe how quarks combine to make two-quark mesons, such as pions and kaons, and three-quark baryons like protons or neutrons.

Possible sightings of tetraquarks have occurred before at KEK, the SLAC National Accelerator Laboratory in Stanford, California, and D-Zero at the Fermilab accelerator in Illinois. It is extremely rare to observe these particles.

Ahmed Ali and colleagues at German Electron Synchrotron (DESY) in Hamburg, Germany, found a 2008 data anomaly in KEK's BELLE experiment, in which the end result from colliding electrons and positrons decayed at too rapid a rate for the suspected particle created. If this particle was a tetraquark, however, then the decay rate would match the experimental results.

Related link
Tetraquark interpretation of the BELLE data on the anomalous Υ(1S)π⁺π^- and Υ(2S)π⁺π^- production near the Υ(5S) resonance

NYTimes.com: XENON100, a new widely anticipated experiment underneath a mountain in Italy designed to detect dark matter particles, did not see anything during a test run last fall, scientists reported Saturday.

But, they said, the clarity with which they saw nothing spurred hopes that such experiments are approaching the rigor and sensitivity necessary to detect the elusive gravitational glue of the cosmos.

The results also cast further doubt on some controversial claims that dark matter has already been seen.

"It's the strongest statement about dark matter today and it reads: we have looked here and there and over there but didn't find nothing," said Rafael Lang of Columbia University, one of the researchers.

A paper describing the work has been submitted to Physical Review Letters.

Related link
First dark matter results from the XENON100 experiment

Nature: Bose–Einstein condensates are ideal tools with which exotic phenomena can be investigated. The hitherto-unrealized Dicke quantum phase transition has now been observed with one such system in an optical cavity.

Science News: If the weird rules of atomic physics do help birds find their way around the globe — as some scientists suspect — a new study has identified ways of finding out how.

The study is among the first to propose a direct test of how quantum entanglement, an effect that inexorably links two electrons in a way that Einstein called “spooky,” could change the behavior of whole animals.

“This paper has really made a contribution by suggesting an experimental test,” comments Thorsten Ritz, a physicist at the University of California, Irvine, who was not involved in the new work.

New Scientist: Pure randomness is surprisingly difficult to create, even if you draw on the inherent randomness of quantum mechanics. Now, though, a "true" random number generator is on the cards, by using entangled "qubits."

ScienceNOW: It's not every day that scientists reduce the uncertainty in a fundamental constant of nature from 30% to 1.5%, but a team of theoretical physicists claims to have done just that.

Using supercomputers and mind-bogglingly complex simulations, the researchers have calculated the masses of particles called "up quarks" and "down quarks" that make up protons and neutrons with 20 times greater precision than the previous standard.

The new numbers could be a boon to theorists trying to decipher particle collisions at atom smashers like Europe's Large Hadron Collider (LHC) or trying to develop deeper theories of the structure of matter.

"It's an audacious claim, and it will have to be looked at very carefully, but I think the result is robust," says Paul Mackenzie, a theorist at Fermi National Accelerator Laboratory in Batavia, Illinois, who was not involved in the work.

Science: Physicists' best chance of spotting an effect of "quantum gravity"—the melding of quantum mechanics and Einstein's theory of gravity—may have evaporated.

According to some quantum-gravity theories, the speed of light may change very slightly with the light's wavelength, and experimenters are searching for the effect in radiation from distant stellar explosions.

Those searches may be in vain, however says Sabine Hossenfelder of the Nordic Institute for Theoretical Physics in Stockholm. If light's speed varied in this way, then untenable paradoxes would arise, she says.

The speed variations must be at least 23 orders of magnitude smaller than experimental limits set last year, she adds.

Related link
The box-problem in deformed special relativity

Nature News: The 'ticks' of the current standard atomic clocks are marked by the regular vibrations of an ensemble of caesium atoms, which vibrate 9.2 billion times every second.

However, noise inherent in the system means that there is a fundamental 'classical limit' to how accurately the clocks can measure those vibrations.

Now two groups, one led by Markus Oberthaler at the University of Heidelberg in Germany, and the other by Philipp Treutlein, then at the Ludwig-Maximilians University of Munich, Germany, have shown that this classical limit can be breached using a quantum twist.

Nature: Non-abelian anyons are hypothesized particles that, if found, could form the basis of a fault-tolerant quantum computer. The theoretical finding that they may turn up in three dimensions comes as a surprise.

Related link
Majorana fermions and non-abelian statistics in three dimensions

Al Jazeera English: The Large Hadron Collider,one of the most expensive experiments in history, started working this week. Al Jazeera English takes a look at the LHC, what it is that scientists are looking for, and whether there are tangible benefits from such an experiment. Interviewees include CERN physicist Jonathan Butterworth, New Scientist's Valerie Jamieson, and biochemist Otto Rossler, who is concerned about the risks associated with running the LHC.

Physics Today: CERN's Large Hadron Collider has finally started colliding two 3.5-TeV circulating beams of protons together to produce 7-TeV collisions and the official start of the LHC research program.

The collisions above (image credit: CERN) occurred at 13:06 Central European Summer Time, according to a live broadcast from CERN, with a couple hundred thousand collisions taken in the first hour.

"It's a great day to be a particle physicist," said CERN director general Rolf Heuer. "A lot of people have waited a long time for this moment, but their patience and dedication is starting to pay dividends."

Science: Have you noticed that computers have stopped getting faster?
Microprocessor clock frequencies plateaued around 2005, a stunning break after a decades-long run of ever-compounding improvements in computing speed.

The cause is a breakdown of the simple constant-electric-field scaling rules that had guided the shrinking of field-effect transistors for decades. As transistors shrank, they switched faster and used less power to switch but a certain amount of power is still needed to switch them from ON to OFF and vice versa.

Companies continue to shrink the transistor, emphasizing the increasing number of parallel processors (cores) they can place on a single silicon chip. But with power supply voltages stuck at about 1 V, increasing clock frequencies as in the past would result in unsupportable increases in power dissipation and heat generation. The transistor is rapidly approaching its ultimate physical limits.

The only way to decisively break the power dissipation bottleneck is to change the physics of transistor operation in ways that facilitate further reduction of operating voltage says Thomas N. Theis and Paul M. Solomon in Science.

Nature News: An obscure class of materials could be used to simulate a slew of exotic particles predicted by physicists

University of Würzburg physicist Laurens Molenkamp has announced some preliminary results from using mercury telluride (HgTe) as a topological insulator to test quantum field theory.

Nature News: Neutrinos like to keep to themselves. These ghostly particles are so reluctant to interact with ordinary matter that billions zip harmlessly through each person every day, and it takes giant, specialized detectors to capture even a handful of them. Now astronomers are finding hints of an even more elusive type of neutrino, one so shy that it could never be detected directly: the sterile neutrino.

"The question of sterile neutrinos is absolutely crucial for nuclear particle physics and astrophysics."

For more than a decade, this subatomic spectre has intrigued theorists and experimenters, but experimental efforts have had trouble catching them. Now, two observations in space—one in microwaves and the other in x rays—are raising hopes again.

Various: Andrew Cleland, John Martinis, and colleagues at the University of California, Santa Barbara, have provided the first clear demonstration that the theory of quantum mechanics applies to the mechanical motion of an object large enough to be seen by the naked eye. Their work satisfies a longstanding goal among physicists.

Nature News: If quantum computing networks are ever to become a reality, physicists must find a way to direct and harness the light emitted in quantum experiments without using cumbersome apparatus.

Now Holger Hofmann, at the Department of Quantum Matter at Hiroshima University in Japan, and his colleagues have developed a way to control the direction of light on the nanoscale. Their technique is based on the workings of the Yagi-Uda antenna commonly used to transmit and detect shortwave radio waves.

Science News: Embracing chaos just might help physicists build a quantum brain. A new study shows that disorder can enhance the coupling between light and matter in quantum systems, a find that could eventually lead to fast, easy-to-build quantum computers.

Related link
Qavity quantum electrodynamics with Anderson-localized modes

Physics Today: Quantum cryptography only works if Alice and Bob share their relative positions in advance.

Now Anthony Laing from the University of Bristol and associates have figured out a new simple protocol that works for particle dimensions of prime or power-prime.

The simplest case in which this works is an entangled pair of qubits, which have been widely used in quantum cryptography experiments.

Laing's protocol can simplify the operation of existing qubit setups and has immediate applications for communication systems such as earth-to-satellite links and the use of integrated photonic waveguides.

The paper also details a photonic implementation of the scheme for entangled pairs of three dimensional particles, so-called qutrits.

The protocol works because security is guaranteed with a measure of the purity on the entanglement shared by Alice and Bob. This kind of measure is robust in an unknown or slowly varying reference frame, yet would reveal the action of any Eavesdropper, (called Eve in this example), as her measurements would strongly and negatively impact the purity. Interestingly, the varying reference frame has no impact at all on the correlations Alice and Bob use determine their secret key.

Crucially, the protocol achieves reference frame independent quantum cryptography without the use of the extra resources which make previous protocols more challenging and in some cases unwieldy.

Related links
Reference frame independent quantum key distribution
Theoretical Breakthrough for Quantum Cryptography MIT Technology Review

Science: What is the formula for the momentum of light zipping through a transparent material? That may sound like a question on a high-school physics quiz, but physicists have been debating the matter ever since two different formulas were proposed more than 100 years ago. Now Stephen Barnett, a theorist at the University of Strathclyde in Glasgow, U.K., says he has resolved the famed "Abraham-Minkowski dilemma." Both formulas are correct, he says, but they denote different things and apply in different contexts.

KEK: The Japanese-led multinational T2K collaboration announced today that they had made the first detection of a neutrino which had travelled 295 km from their neutrino beamline at the Japanese Proton Accelerator Research Complex (J-PARC) facility in Tokai village to the Super- Kamiokande underground neutrino detector near the west coast of Japan.

"Switching on one of the world's first neutrino superbeams is a great achievement," said CERN Director General Rolf Heuer. "Even in a time of financial difficulty around the globe, it's important not to lose sight of the fact that basic science is and always will be a crucial element of progress. It is therefore heartening to see such an important new basic science initiative getting underway now."

"It is a big step forward," said T2K spokesperson Takashi Kobayashi. "We've been working hard for more than 10 years to make this happen."
 

J-PARC now produces the world's most powerful neutrino beams to study neutrino oscillations.
 

"Neutrinos are the elusive ghosts of particle physics," Kobayashi explains. "They come in three types, called electron neutrinos, muon neutrinos, and tau neutrinos, which used to be thought to be immutable."
 

Interacting only weakly with matter, neutrinos can traverse the entire earth with vastly less attenuation than light passing through a window. The very weakness of their interactions allows physicists to make what should be very accurate predictions of their behavior, and thus it came as a shock when measurements of the flux of neutrinos coming from the thermonuclear reactions which power our sun were far lower than predicted.

A second anomaly was then clearly demonstrated in 1998 by Super-Kamiokande, when it showed that the flux of different types of neutrino generated within our atmosphere by cosmic ray interactions was different depending on whether the neutrinos were coming from above or below (which should not have been possible given our understanding of particle physics). Other experiments, such as Kamioka Liquid scintillator Anti-Neutrino Detector (KamLAND), have conclusively demonstrated that these anomalies are caused by neutrino oscillations, whereby one type of neutrino turns into another.

The first T2K event seen in Super-Kamiokande is seen in the image above. Each dot is a photomulipler tube which has detected photons. The two circles of hits indicate that a neutrino has probably produced a particle called a π 0, perfectly in time with the arrival of a pulse of neutrinos from J-PARC. Another faint circle surrounds the viewpoint of this image, showing a third particle was created by the neutrino.

The T2K experiment has been built to make measurements of unprecedented precision of known neutrino oscillations, and to look for a so-far unobserved type of oscillation which would cause a small fraction of the muon neutrinos produced at J-PARC to become electron neutrinos by the time they reach Super-Kamiokande.
 

Observing the new type of oscillation would open the prospect of comparing the oscillations of neutrinos and anti-neutrinos, which many theorists believe may be related to one of the great mysteries in fundamental physics—why is there more matter than anti-matter in the universe? "The observation of this first neutrino means that the hunt has just begun," said Koichiro Nishikawa, director of the Institute for Particle and Nuclear Studies at KEK and founder of T2K. "The first physics results are expected later this year." Today's news he says, "is the beginning."

Science: A view of a coastline appears as a fractal—an object that appears the same at all length scales (perhaps only statistically).

Fractals actually abound in nature, but fractals can occur in the quantum realm as well, even though they have never been observed there, until, perhaps, now.

In Science, Anthony Richardella and associates report direct measurements of quantum mechanical electron waves that indicate that they may also possess a fractal nature.

Related link
Visualizing critical correlations near the metal-insulator transition in Ga_1-xMn_xAs

Nature: A technique used primarily to study fundamental issues in quantum mechanics has now been shown to have promise as a powerful practical tool for making ultra-precise measurements.

APS Meeting - New Scientist: Several times a month, teams of astronomers from three observatories blast the Moon with pulses of light from a powerful laser and wait for the reflections from a network of mirrors placed on the lunar surface by the Apollo missions, as well as two Soviet Lunokhod landers.

By timing the light's round trip, they can pinpoint the distance to the Moon with an accuracy of around a millimeter—a measurement so precise that it has the potential to reveal problems with general relativity.

But now Tom Murphy from the University of California, San Diego, thinks the mirrors have become coated in Moon dust. "The lunar reflectors are not as good as they used to be by a factor of 10," he says.

APS Meeting: Physics Today: Physicists at Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC) have discovered some additional experimental hints of why there is matter in the universe by replicating the conditions of the first microseconds after the Big Bang.

The results from RHIC's Pioneering High Energy Nuclear Interaction eXperiment (PHENIX) and STAR detector were discussed at the April meeting of the American Physical Society yesterday and published in Physical Review Letters.

When the Big Bang occurred, according to the symmetry rules that govern the universe, equal parts of matter and antimatter should have been created leading to all matter being annihilated. But this was not the case: Why?

A hot start

To find out, you have to replicate conditions of the early universe. RHIC can duplicate the conditions of the first microseconds by colliding gold atoms together near the speed of light. The resulting collision is hot enough to melt protons and neutrons into a quark gluon plasma, according to the PHENIX's researchers.

Predictions made prior to RHIC's initial operations in 2000 expected that the quark-gluon plasma would exist as a gas. But RHIC's first three years of operation showed that the matter produced at RHIC behaves as a liquid, whose constituent particles interact very strongly among themselves. This liquid matter has been described as nearly "perfect" in the sense that it flows with almost no frictional resistance, or viscosity. Such a "perfect" liquid doesn't fit with the picture of "free" quarks and gluons physicists had previously used to describe the quark-gluon plasma.

In papers published in 2005, RHIC physicists laid out a plan of crucial measurements to clarify the nature and constituents of this "perfect" liquid. Measuring the temperature early in the collisions was one of those goals. Models of the evolution of the matter produced in RHIC collisions had suggested that the initial temperature might be high enough to melt protons, but a more direct measurement of the temperature required detecting photons—particles of light—emitted near the beginning of the collision, which travel outward undisturbed by their surroundings.

"This was an extraordinarily challenging measurement," explained PHENIX spokesperson Barbara Jacak. "There are many ways that photons can be produced in these violent collisions. We were able to 'eliminate' the contribution from these other sources by exploiting RHIC's flexibility to measure them directly and to make the same measurement in collisions of protons, rather than of gold nuclei. Thus we could pin down excess production in the gold-gold collisions, and determine the temperature of the matter that radiated the excess photons. By matching theoretical models of the expanding plasma to the data, we can determine that the initial temperature of the 'perfect' liquid has reached about four trillion degrees Celsius." At its hottest stage, the infusion may reach 7 trillion °C.

"This is the hottest matter ever created in the laboratory" and qualifies as the "highest temperature known in our present universe," said Steven Vigdor, Brookhaven's associate laboratory director for nuclear and particle physics, who oversees research at RHIC.

Breaking the universe's rules

Cosmologists have predicted that the solution to this dichotomy of why equal amounts of matter and antimatter were not created would be bubbles or local regions in which there would be a breakdown in the existing rules governing the behavior of particles in the universe.

The symmetry "rule" suggests that events should occur in exactly the same way whether seen directly or in a mirror, with no directional dependence. But STAR has observed regions in the quark-gluon plasma at the heart of the RHIC collisions in which asymmetric charge separations occurs.

STAR observed that positively charged quarks may prefer to emerge parallel to the magnetic field in a given collision event, while negatively charged quarks prefer to emerge in the opposite direction. Because this preference would appear reversed if the situation were reflected through a mirror, it appears to violate mirror symmetry.

"In all previous studies of systems governed by the strong force among quarks and gluons, it has been found to very high precision that events and their mirror reflections occur at exactly the same rate, with no directional dependence," said Vigdor. "So this observation at STAR is truly intriguing."

STAR data also suggest the local breaking of another form of symmetry, known as charge conjugation–parity or CP invariance. According to this fundamental physics principle, when energy is converted to mass or vice versa according to Einstein's famous E=mc² equation, equal numbers of particles and oppositely charged antiparticles must be created or annihilated. If CP symmetry had not been broken at some very early time in the evolution of our universe, the particles and antiparticles created in equal numbers in the Big Bang would subsequently have annihilated one another in pairs, leaving no matter to form the galaxies, stars, planets.

While some small violations of CP symmetry have been found in previous laboratory experiments, those violations are far too weak to account for the amount of matter remaining in the universe today.

"These new results thus suggest that RHIC may have a unique opportunity to test in the laboratory some crucial features of symmetry-altering bubbles," said Vigdor.

The signs of possible local CP violation at STAR cannot completely explain the global predominance of matter in today's universe, but they may offer some insight into how such symmetry violations occur. CERN's Large Hadron Collider, which restarts this week, will eventually produce collisions 3 times more powerful than those at RHIC to see if this quark-gluon plasma actually does transition into a gas.

RHIC will be upgraded over the next few years to investigate these broken symmetry effects more closely but there could also be less sexy explanations for the observed charge separation, said Berndt Mueller, a theorist at Duke University in Durham, North Carolina, to ScienceNOW's Lauren Schenkman. If more refined analyses do turn up conclusive evidence of parity violation, it would be like mining for silver and finding gold, said Mueller.

Paul Guinnessy

Related coverage
Atom smasher shows vacuum of space in a twist New Scientist
The hottest science experiment on the planet Discover magazine
Scientists re-create high temperatures from Big Bang USA Today
Hottest temperature ever heads science to Big Bang Reuters
In Brookhaven collider, scientists briefly break a law of nature New York Times
Particle collision puts twist in early universe ScienceNOW

Science: The different colors on the surface of a soap bubble arise from the interference of light waves reflecting from the outer and inner surface of the liquid film. As the thickness of the film varies, so will the wavelength of light that undergoes constructive interference and remains visible.

According to quantum mechanics, even material particles such as electrons behave like waves. In addition to their charge, electrons also have two distinguishable spin states, spin-up and spin-down.

In Science, Petta and associates demonstrate beam splitting and interferometry for the spin degrees of freedom of two electrons on a semiconductor chip.

Related link
A coherent beam splitter for electronic spin states

Science News: Groups at Harvard and the University of Queensland in Brisbane, Australia, have designed and built a quantum computer to simulate and calculate the behavior of a molecular, quantum system.

The simulation mimics reality exactly.

New Scientist: A complex 248-dimensional symmetry called E₈ has been glimpsed in laboratory experiments on exotic crystals.

Radu Coldea of the University of Oxford and his colleagues chilled a crystal made of cobalt and niobium to 0.04 °C above absolute zero. Atoms in the crystal are arranged in long, parallel chains. Because of a quantum property called spin, electrons attached to the atom chains act like tiny bar magnets, each of which can only point up or down.

Applying a 5.5-Tesla magnetic field perpendicular to the direction of the electrons create spontaneous patterns in the electron spins in the chains, some of which match the E₈ structure.

Related link
Quantum Criticality in an Ising Chain: Experimental Evidence for Emergent E₈ Symmetry

Nature: The peculiar ultra-fast trembling motion of a free electron—the Zitterbewegung predicted by Erwin Schrödinger in 1930 when he scrutinized the Dirac equation—has been simulated using a single trapped ion.

Related article
Quantum simulation of the Dirac equation

NYTimes.com: He is good-natured, funny, and thought to be among the smartest men in physics: Frank A. Wilczek, 58, a professor at the Massachusetts Institute of Technology, was one of three winners of the 2004 Nobel Prize in Physics and is a frequent columnist for Physics Today.

The award came for work Wilczek had done in his 20s, with David Gross of Princeton University, on quantum chromodynamics, a theoretical advance that is part of the foundation of modern physics.

The New York Times provides an edited version of two conversations with Wilczek, in October and this month.

Science: Predicting the binding rules of quantum particles is a formidable task.

Even for as few as three particles, one would need to know precisely all the details of the mutual interactions among them.

Notable exceptions have been predicted to arise if the interaction between the particles is very large, a condition where universal binding laws are expected to appear.

Because no available physical system composed of atoms, nuclei, or even elementary particles was suitable to observe the phenomenon, these ideas have been mainly confined to theory.

In Science, Scott E. Pollack and colleagues present evidence for the presence of universal scaling laws simultaneously occurring for three- and four-body bound states in an ultracold atomic system.

The observation confirms both old and new theoretical predictions, thus providing a fuller understanding of universal binding.

Related Links
Universal few-body binding
Universality in three- and four-body bound states of ultracold atoms

Science News: A cloud of ultracold atoms can store a beam of yellow light for 1.5 seconds, says a new paper by researchers led by Lene Hau of Harvard University.

The new study is "a beautiful demonstration," says Irina Novikova, a physicist at the College of William & Mary in Williamsburg, Virginia. Before this result, she says, light storage was measured in milliseconds. "Here, it's fractional seconds. It's a really dramatic time."

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Creation of long-term coherent optical memory via controlled nonlinear interactions in Bose–Einstein condensates

Physics Today: Google is working on developing a quantum computer, announced Google's Hartmut Neven at the Neural Information Processing Systems conference (NIPS 2009) in Vancouver, Canada, last week.

Neven, who is the company's technical lead manager for image recognition, gave details of the presentation on the Google research blog.

The reason for Google's interest in quantum computing is speed. As the size of the internet increases exponentially it is becoming harder and harder for Google to maintain the fast speed of the service without having to resort to building massive server farms.

A quantum-based computer could speed up searches dramatically and add a new layer of features to google's existing features, especially on images. As Neven states in the blog:

Assume I hide a ball in a cabinet with a million drawers. How many drawers do you have to open to find the ball? Sometimes you may get lucky and find the ball in the first few drawers but at other times you have to inspect almost all of them. So on average it will take you 500,000 peeks to find the ball. Now a quantum computer can perform such a search looking only into 1000 drawers. This mind boggling feat is known as Grover's algorithm.

The company has spent three years working on quantum adiabatic algorithms with the Canadian company D-Wave providing the hardware.

D-Wave's processors work by magnetically coupling superconducting loops called rf-SQUID flux qubits. "It is not easy to demonstrate that a multi-qubit system such as the D-Wave chip indeed exhibits the desired quantum behavior," says Neven.

At NIPS 2009 Neven demonstrated what google had achieved so far. The company built a detector that has learned to spot cars by looking at example pictures. "There are still many open questions," says Neven, "but in our experiments we observed that this detector performs better than those we had trained using classical solvers running on the computers we have in our data centers today."

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Primer in quantum algorithms
Training a large scale classifier with the quantum adiabatic algorithm
NIPS 2009 demonstration: Binary classification using hardware implementation of quantum annealing

Science: From early childhood we know that to interact with an object, we have either to go to it or to throw something at it. Yet, contrary to all our daily experience, there are spatially separated quantum systems that exhibit nonlocal correlations. Exploring how nature performs its trick of quantum nonlocality has led to new experiments that provide a deeper understanding of the tension between quantum physics and relativity and to proposals for disruptive technologies.

Science News: Studying with the radio on may not be the best way to remember what you've read. But scientists have now built a data storage device whose memory gets a boost from noise.

The device can store one bit of information, such as a 0 or a 1, only when surrounded by electronic noise, which is normally a problem in computer circuits.

"If you remove the noise, it doesn't store the bit at all," says Diego Grosz of the Instituto Tecnológico de Buenos Aires, a coauthor of the study.

Related Link
One-bit stochastic resonance storage device

ScienceNOW: The way light moves, with its fixed speed and its ability to act like either a wave or a particle, often leads to some of the most curious paradoxes of physics. A new one has just been found: Make holes in a film of gold so thin that it's already semitransparent, and less light gets through.

Nature: Quantum systems habitually leak information, limiting their usefulness for practical applications. By optimally reversing the leak, this information loss has been reduced to a trickle in the solid state.

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Preserving electron spin coherence in solids by optimal dynamical decoupling

Science: Since the work of James Clerk Maxwell and Heinrich Hertz, we have known that light is an electromagnetic wave. An intricate mechanism generates magnetic fields around the electric fields, and vice versa. In the optical-wavelength range, experimental studies have been limited to probing only the electric-field components.

In Science, Matteo Burresi and colleagues report direct measurements of the magnetic-field components of light obtained with a nanostructured metallic probe at the tip of a sharp glass fiber.

Related Link
Probing the magnetic field of light at optical frequencies

Various: In a talk entitled Higgs, dark matter and supersymmetry, what the Large Hadron Collider will tell us, given to science writers attending the Council for the Advancement of Science Writing’s annual symposium, Nobel laureate Steven Weinberg of the University of Texas at Austin gave his opinion of what the LHC will discover.

The LHC will eventually attain sufficient energy to produce the Higgs boson, he says, but evidence of supersymmetry is a much more speculative possibility.

"If the Congress had not had the imbecility to cancel the Superconducting Super Collider [in 1993], it would have been discovered long ago here in Texas," says Weinberg in comments reported by Tom Siegfried of Science News.

"Many of us are terrified that the LHC will discover a Higgs particle and nothing more," Weinberg said. That would just confirm the standard model, which everybody believes already. It would not point the way to further progress in solving a deeper problem that physics faces—how to add gravity to the unified theory of the other forces.

Peter Woit of "Not Even Wrong" says that what he found interesting about Weinberg’s talk was that, "whatever Weinberg’s views on more speculative theories in physics such as extra dimensions or string theory landscape, he decided not to mention these at all in his talk."

"As a result, both questioners wanted to ask Weinberg about string theory, which he hadn’t talked about, not about the solid science he did talk about," says Woit.

String theory or superstring theory, is one of the candidates for unifying all the forces in the universe into one theory.

If the LHC creates new particles generated by supersymmetry, then clues to what makes up the bulk of dark matter in the universe would be found, which may give some tangible evidence to whether string theory is correct.

But string theory to this point has not produced a cohesive and clear guide to testing its fit with all the observable features of physical existence. Weinberg said:

"It’s developed mathematically, but not to the point where there is any one theory, or to the point that even if we had one theory we would know how to do calculations to predict things like the mass of the electron, or the masses of the quarks. So, I would say, although there has been theoretical progress... I find it disappointing. One of the hopes would be that the LHC would provide a clue to something we’re missing in superstring theory and I think that supersymmetry is the most likely place to look."

"One of the troubles with superstring theory is that although in a sense the theorists think there is only one theory, there are an infinite number of approximate solutions of it and we don’t know which one corresponds to our world. But at least in a large variety of the solutions of superstring theory there is supersymmetry visible at low energies, and if we see supersymmetry at low energies, superstring theorists may be able to derive from it some kind of clue as to how to solve these theories. But I haven’t talked about it in this lecture because I don’t see how that would work... I mean I couldn’t say that it was likely with any degree of sincerity, and certainly the LHC and any other accelerator that we can imagine being built will not get up to energies which are high enough so that we can directly see the structures that are described by superstring theory, the strings or the D-branes or whatever it is. Those will not be accessible at the LHC, so any clue we get will be very indirect."

"I myself, well I was working on superstring theory in the 80s and gave it up because... I moved into cosmology, which in the last couple of decades has had the excitement that elementary particle physics had in the 60s and 70s, a wonderful coming together of theory and observation. Cosmology now reminds me of the excitement that I felt when I was younger and doing particle physics... and it’s a pity that superstring hasn’t developed better. I still think it’s the best hope we have, I don’t know of anything else. My own work very recently has been trying to develop an alternative to superstring theory as a way of making sense out of quantum gravity at very high energies. But even though I’m working on this I still find superstring theory more attractive, but not attractive enough…"

ISNS: With the speed of computers so regularly seeing dramatic increases in their processing speed, it seems that it shouldn't be too long before the machines become infinitely fast—except they can't.

A pair of physicists has shown that computers have a speed limit as unbreakable as the speed of light. If processors continue to accelerate as they have in the past, we'll hit the wall of faster processing in less than a century.

Intel cofounder Gordon Moore predicted 40 years ago that manufacturers could double computing speed every two years or so by cramming ever-tinier transistors on a chip. His prediction became known as Moore's Law, and it has held true throughout the evolution of computers—the fastest processor today beats out a 10-year-old competitor by a factor of about 30.

If components are to continue shrinking, physicists must eventually code bits of information onto ever smaller particles. Smaller means faster in the microelectronic world, but physicists Lev Levitin and Tommaso Toffoli at Boston University in Massachusetts, have slapped a speed limit on computing, no matter how small the components get.

"If we believe in Moore's law ... then it would take about 75 to 80 years to achieve this quantum limit," Levitin said.

"No system can overcome that limit. It doesn't depend on the physical nature of the system or how it's implemented, what algorithm you use for computation ... any choice of hardware and software," Levitin said. "This bound poses an absolute law of nature, just like the speed of light."

Scott Aaronson, an assistant professor of electrical engineering and computer science at the Massachusetts Institute of Technology in Cambridge, thought Levitin's estimate of 75 years extremely optimistic.

Moore's Law, he said, probably won't hold for more than 20 years.

In the early 1980s, Levitin singled out a quantum elementary operation, the most basic task a quantum computer could carry out. In a paper published in Physical Review Letters, Levitin and Toffoli present an equation for the minimum sliver of time it takes for this elementary operation to occur. This establishes the speed limit for all possible computers.

Using their equation, Levitin and Toffoli calculated that, for every unit of energy, a perfect quantum computer spits out ten quadrillion more operations each second than today's fastest processors. 

"It's very important to try to establish a fundamental limit—how far we can go using these resources," Levitin explained.

The physicists pointed out that technological barriers might slow down Moore's law as we approach this limit. Quantum computers, unlike electrical ones, can't handle "noise"—a kink in a wire or a change in temperature can cause havoc. Overcoming this weakness to make quantum computing a reality will take time and more research.

As computer components are packed tighter and tighter together, companies are finding that the newer processors are getting hotter sooner than they are getting faster. Hence the recent trend in duo and quad-core processing; rather than build faster processors, manufacturers place them in tandem to keep the heat levels tolerable while computing speeds shoot up. Scientists who need to churn through vast numbers of calculations might one day turn to superconducting computers cooled to drastically frigid temperatures. But even with these clever tactics, Levitin and Toffoli said, there's no getting past the fundamental speed limit.

Aaronson called it beautiful that such a limit exists.

"From a theorist's perspective, it's good to know that fundamental limits are there, sort of an absolute ceiling," he said. "You may say it's disappointing that we can't build infinitely fast computers, but as a picture of the world, if you have a theory of physics allows for infinitely fast computation, there could be a problem with that theory."

Lauren Schenkman
First published at Inside Science News Service

NYTimes.com: Holger Bech Nielsen, of the Niels Bohr Institute in Copenhagen, and Masao Ninomiya of the Yukawa Institute for Theoretical Physics in Kyoto, Japan, have suggested that the hypothesized Higgs boson, which physicists hope to produce with CERN's Large Hadron Collider, might be so abhorrent to nature that its creation would ripple backward through time and stop the collider before it could make one, like a man who goes back in time to kill his grandfather.

Nielsen and Ninomiya put this idea forward in a series of papers: "Test of Influence from Future in Large Hadron Collider: A Proposal" and "Search for Effect of Influence from Future in Large Hadron Collider," posted on the physics website arXiv.org.

According to the so-called standard model that rules almost all physics, the Higgs is responsible for imbuing other elementary particles with mass.

"It must be our prediction that all Higgs producing machines shall have bad luck," Nielsen told the New York Times in an e-mail.

Science News: By linking the electrical currents of two superconductors large enough to be seen with the naked eye, researchers have extended the domain of observable quantum effects. Billions of flowing electrons in the superconductors can collectively exhibit a weird quantum property called entanglement, usually confined to the realm of tiny particles, say scientists in Nature.

"It's an exciting piece of work," comments physicist Steven Girvin of Yale University. "People are interested in pushing the boundaries of quantum mechanics."

Nature News: Suspending a cat between life and death is one of the best-known thought experiments in quantum mechanics.

Now researchers from Germany and Spain are proposing a real experiment to probe whether a virus can exist in a superposition of two quantum states.

Such superpositions are typically the domain of smaller, inanimate objects such as atoms. But the team believes that their technique, using finely tuned lasers, will soon allow for the superposition of something much closer to a living organism. They outline the experiment in a paper posted to the arXiv pre-print server.

Related Link
Towards quantum superposition of living organisms

Science: The Moon isn't made of green cheese and almost certainly doesn't harbor hypothetical particles called "strangelets," an analysis of lunar soil has shown. The result undermines a possible strangelet sighting a decade ago and strengthens the case that the bizarre particles, which protesters once feared might emerge from an atom smasher and consume Earth, don't exist.

"I'm not surprised," says Frank Wilczek, a theorist at the Massachusetts Institute of Technology (MIT) in Cambridge. "It would be a great discovery to find strangelets, but the theoretical case for them is pretty shaky." Still, he says, "it's not crazy" to look for them.

Forbes.com: Outsider Peter Woit is challenging the debate about physics "theory of everything."

NYTimes.com: IBM researcher Frances Ross is growing a crop of mushroom-shaped silicon nanowires that may one day become a basic building block for a new kind of electronics.

Nanowires are just one example, although one of the most promising, of a transformation now taking place in the material sciences as researchers push to create the next generation of switching devices smaller, faster, and more powerful than today's transistors.

The reason that many computer scientists are pursuing this goal is that the shrinking of the transistor has approached fundamental physical limits.

guardian.co.uk: For all we know we may live in a world in which windows unbreak and cold cups of coffee spontaneously heat up, we just don't remember. The explanation is quantum entanglement, says Lorenzo Maccone at the Massachusetts Institute of Technology, but other physicists, such as Huw Price, head of the Centre for Time at the University of Sydney, remain skeptical.

Related Link
Quantum Solution to the Arrow-of-Time Dilemma Phys. Rev. Lett.

Various: NOνA is a collaboration of 180 scientists and engineers from 28 institutions which plans to study neutrino oscillations using the existing NuMI neutrino beam at Fermilab. The NOνA experiment is designed to search for oscillations of muon neutrinos to electron neutrinos by comparing the electron neutrino event rate measured at the Fermilab site with the electron neutrino event rate measured at a location just south of International Falls, Minnesota, 810 kilometers distant from Fermilab. If oscillations occur, the far site will see the appearance of electrons in the muon neutrino beam produced at Fermilab.

As the Washington Post describes it in this story:

Scientists are playing an exotic game of pitch and catch between Illinois and Minnesota. Their catcher's mitt is solid iron, weighs 5,500 tons, and is parked in northern Minnesota in an abandoned iron mine. With millions of dollars from the federal stimulus package, construction crews are now building a second mitt near the Canadian border. It's even heavier, some 15,000 tons, and is made of 385,000 liquid-filled cells of PVC plastic.

Five hundred miles to the south is the pitcher: Fermilab, a sprawling U.S. government laboratory west of Chicago where physicists do violent things with tiny particles.

Science News: In a new study, researchers found telltale signs of quantum weirdness lurking in an optical trick called ghost imaging. Discovered over a decade ago, ghost imaging allows researchers to create an image of something using light that never bounced off the actual object. The new work adds to the debate over whether ghost imaging is quantum in nature, or if normal, everyday physics can explain the phenomenon.

Related Link
Holographic Ghost Imaging and the Violation of a Bell Inequality. Physical Review Letters, in press

Technology Review: Researchers at the National Institute of Standards and Technology (NIST) in Boulder, CO, have demonstrated multiple computing operations on quantum bits—a crucial step toward building a practical quantum computer.

Nature News: Until recently, string theory—long heralded as a 'theory of everything'—hadn't been particularly good at explaining anything.

But at a workshop this month at the Kavli Institute for Theoretical Physics in Santa Barbara, California, scientists have been using the theory to make progress in tackling one of the biggest puzzles in condensed-matter physics: the origin of high-temperature superconductivity.

Science News: A team of theoretical physicists and astronomers has calculated that any hidden extra dimension beyond our familiar three-dimensional space, a world known in physics parlance as a 3-brane, must be less than 3 micrometers. The researchers base their findings on the recent discovery of one of the smallest and oldest black holes ever found.

The new limit is less than half that of previous limits on the length of an extra dimension, Oleg Gnedin of the University of Michigan in Ann Arbor and his colleagues report in a study posted online 30 June (http://arxiv.org/abs/0906.5351).

Nature: LaHaye and colleagues have taken an important step towards the observation of quantum phenomena in nearly macroscopic moving objects.

They report experimental evidence of an intriguing interplay between a superconducting artificial atom and a micrometre-size mechanical resonator. Remarkably, their findings can be described using the 'language' of radiation–matter interactions, which has also been successful in explaining the coupling of a superconducting artificial atom to microwave photon.

Related Link
Nanomechanical measurements of a superconducting qubit

ScienceNOW: The first electric motor whirred to life nearly 2 centuries ago, and in recent decades scientists and engineers have worked to build ever-smaller ones.

Now, a team of theoretical physicists has proposed a fully quantum-mechanical version of the classic spinning electric motor that consists of just two atoms trapped in a ring of light.

Experimenters might be able to construct the thing now, the researchers say, even though they themselves don't have an intuitive explanation of exactly how it works.

Nature: For almost a century, physicists have had in hand "the" theoretical framework of the known world—quantum mechanics. But whereas the world clearly comprises large complex systems, quantum mechanics is usually associated with the microworld of atoms and elementary particles, and is hardly ever considered as an underlying feature in our daily life.

This is even more pronounced for some of the seemingly weird predictions of quantum mechanics, such as entanglement, which asserts that the quantum state of physically separated objects is mutually and inextricably connected.

J. D. Jost and colleagues in Nature demonstrate quantum entanglement of two spatially separated mechanical oscillators. Although the quantum nature of mechanical oscillators has been known and observed for a long time, the entanglement of their oscillating motions has not, and its demonstration adds a valuable tool to the toolbox of quantum-state engineering.

Related Links
Entangled mechanical oscillators

Nature: The ability to produce arbitrarily superposed quantum states is a prerequisite for creating a workable quantum computer. Such highly complex states can now be generated on demand in superconducting electronic circuitry.

Related Link
Synthesizing arbitrary quantum states in a superconducting resonator

AFP: A team of French physicists led by Jean-Yves Bigot of the Institute of Materials Physics and Chemistry in Strasbourg say they have used a "femtosecond" laser, using ultra-fast bursts of laser light, to alter electron spin and thus speed up retrieval and storage.

The technique could increase the speed at which data is written and read from a hard drive up to 100,000 times, they say in this week's Nature Physics.

The work builds upon Albert Fert and Peter Gruenberg's discovery that tiny changes in magnetic fields can yield a large electric output. Their research led to the creation of a new electronics field called "spintronics" that relies on electron spin to store data; however, sensors for reading that data until now were too slow to be effective.

"Our method is called the photonics of spin, because it is photons [particles of light] that modify the state of the electrons' magnetisation" on the storage surface, Bigot told AFP.

Related Physics Today articles

Discoverers of Giant Magnetoresistance Win this Year's Physics Nobel (December 2007)
Quantum Spin Hall Effect Shows up in a Quantum Well Insulator, Just as Predicted (January 2008)
Magnetic Semiconductors Enable Efficient Electrical Spin Injection (April 2000)

Related Link

Coherent ultrafast magnetism induced by femtosecond laser pulses

In last week's Science Kukushkin and colleagues describe a variant of this technique for measuring the energy and momentum dependence of the excitations of a two-dimensional (2D) electron system.

In this technique, momentum is imparted with sound and, separately, energy is imparted with light. This approach allows the spectrum of "magnetorotons"—characteristic excitations of the states associated with the fractional quantum Hall effect—to be measured directly.
The observed spectral features were predicted many years ago but have eluded direct measurement until now.

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Dispersion of the Excitations of Fractional Quantum Hall States

Science: Graphene holds enormous promise for transistors and other electronic devices. But it is already making an impact in the arcane world of high-energy physics.

That's because electrons in graphene don't behave like electrons in a standard metal. In the lattice of a typical metal, electrons feel the push and pull of surrounding charges as they move. As a result, moving electrons behave as if they have a different mass from their less mobile partners. When electrons move through graphene, however, they act as if their mass is zero--behavior that makes them look more like neutrinos streaking through space near the speed of light.

At such "relativistic" speeds, particles don't follow the usual rules of quantum mechanics. Instead, physicists must invoke the mathematical language of quantum electrodynamics, which combines quantum mechanics with Albert Einstein's relativity theory. Even though electrons course through graphene at only 1/300 the speed of neutrinos, physicists realized several years ago that the novel material might provide a test bed for studying relativistic physics in the lab.

"This is pretty cool," says Alan Migdall of the National Institute of Standards and Technology in Gaithersburg, Maryland. "I haven't seen an approach like this before." Still, he and others say it's too soon to tell whether the new method, described on page 483 in Science, will outshine techniques that generate pairs of photons entangled from "birth."

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An entanglement filter

Related Article
Ballistic spin resonance

The water level at Homestake is down 254 feet since the high-water mark was reached last August.

Homestake is 8,000 feet deep. Mining stopped in 2001, and the underground pumps were turned off just before Homestake was sealed shut in 2003. Water was slowly filling the mine until last year. Now, the South Dakota Science and Technology Authority is pumping water out to reopen Homestake as an underground laboratory, with experiments as deep as 4,850 feet underground

ScienceNOW: This might be a rare case about which Einstein was wrong. More than 60 years ago, the great physicist scoffed at the idea that anything could travel faster than light, even though quantum mechanics had suggested such a condition. Now four Swiss researchers have brought the possibility closer to reality. Testing a concept called "spooky action at a distance"--a phrase used by Einstein in criticizing the phenomenon--they have shown that two subatomic particles can communicate nearly instantaneously, even if they are separated by cosmic distances.

Nature: A vacuum may be devoid of matter, but its shape is still important. The strength of the Casimir force caused by quantum fluctuations in the space between surfaces is critically dependent on their nanometre-scale shape.

Science: Images are superb conveyors of information. Recent research has shown how subtle quantum mechanical aspects of light can profoundly influence the nature of image formation.In the July 25 issue of Science, two important advances in this emerging area of quantum imaging are presented. Wagner et al. report on the behavior of two beams of light that are quantum mechanically entangled in position and direction of propagation--that is, the outcome of measurements on one beam depends on what sort of measurements have been performed on the other beam. Boyer et al. show that two image-bearing light beams can be entangled such that strong quantum correlations exist both between the two beams and between individual image features within each beam. They find two sorts of quantum correlations: The intensities of the two beams fluctuate in unison, at a level not permitted by classical statistics, and the noise in one part of the light field can be reduced, or "squeezed," at the expense of another part.

Science News: The length of bonds connecting water molecules could demonstrate quantum effects and help explain some of water’s weirdness.

Nature: Traditionally, entanglement was considered to be a quirk of microscopic objects that defied a common-sense explanation. Now, however, entanglement is recognized to be ubiquitous and robust. With the realization that entanglement can occur in macroscopic systems — and with the development of experiments aimed at exploiting this fact — new tools are required to define and quantify entanglement beyond the original microscopic framework.

Nature: A joint exploration of early modern physics and the surreal art movement shows these twentieth-century revolutions had more in common than we thought, explains Nature's Philip Ball.