Nature: LS Cable, a South Korean company based in Anyang-si near Seoul, is taking part in a program to modernize South Korea's electricity grid. As part of that effort, LS Cable has ordered 3000 km of high-Tc superconducting wire from the Devens, Massachusetts-based American Superconductor. Although the dollar value of the sale has not been announced, its scale makes it the largest for superconducting wire. Nature's Joseph Milton reports on the deal and its implications.
Recently in Condensed Matter Physics Category
New York Times: In December 1942, John Pritchard and two other Coast Guard aviators were listed as missing after their plane lost radio contact—and presumably crashed—during a storm off the southeast coast of Greenland.
Now, 68 years later, the Coast Guard has commissioned a private recovery team to try to locate, excavate and repatriate the three men entombed in a J2F-4 Grumman Duck biplane (see left image) buried in a glacier there. The team set out last month with an arsenal of top-of-the-line technology: ground-penetrating radar, which can detect metallic objects close to the surface; advanced ice-melting equipment, which can pinpoint buried objects as it dissolves the ice around them; a camera that can take pictures from inside deep hollows of ice; and sensors to track the speed the glacier is moving before the plane, and bodies move out to sea.
Nature: At low temperatures and high pressure, helium completely solidifies, or does it? In 2004 Eun-Seong Kim and Moses Chan of the Pennsylvania State University found evidence of a phase within frozen He that appeared to flow through the solid like a liquid. Since their experiment, the nature of "supersolidity" has been unresolved: Is it a true many-body quantum phenomenon or is it the result of imperfections in the solid? Nature's Eugenie Samuel Reich reports on recent experiments that might resolve the question.
BBC: Researchers from Australia and the US have created a transistor a mere seven atoms in size and only four-billionths of a meter across. Although not the smallest ever created, it is embedded in a single silicon crystal and is 10 times smaller than those used in contemporary computers. The ongoing goal of computer hardware development has been to make machines that are faster, cheaper, and able to store more data. Michelle Simmons at the University of New South Wales and coworkers, who published their results in Nature Nanotechnology, hope that their tiny transistor will lead to the development of a solid-state quantum computer.
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.
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
symmetry: Business in the particle accelerator world is booming, as is business at Advanced Energy Systems, where Tony Favale is president. His company is doing research and design work for the next generation of accelerators, which will be employed in electron lasers for the Navy, radiation detectors for the Department of Homeland Security, and more efficient particle colliders at US national laboratories.
But of the seven positions he was advertising in November, three were still unfilled in mid-March because Favale can't find enough qualified accelerator scientists.
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.
Nature: Dorothy Hodgkin was born 100 years ago next month. When Hodgkin won the Nobel Prize in Chemistry in 1964, much was made of her gender. She was only the fifth woman to become a laureate in science, the first from Britain, and the first women not married to a scientist.
Hodgkin was therefore by definition exceptional. When Georgina Ferry began to write her biography soon after her death in 1994, one of her principal motives was to try to understand what it was that had enabled her to transcend the conventions of her time. "She never acknowledged that she faced barriers on the grounds of her gender," writes Ferry, "and her story largely bears this out."
What did influence her social and scientific circumstances were also exceptional, and provided the environment in which it was possible for her to fulfil her promise and achieve science's highest honor, says Ferry. The support of her parents, and the forward-thinking planning of Somerville College in Oxford.
Physics Today: Updated 4/7/2010: According to sources at Lawrence Livermore National Laboratory, element number 117 has been successfully synthesized.
There were hints that element 117 had been discovered at the recent 31st meeting of the Program Advisory Committee for Nuclear Physics, but the news became public when a paper describing the research was accepted for publication in Physical Review Letters.
Continue reading Element 117 discovered.
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.
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.
Continue reading The impact of the LHC on society and physics.
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."
Continue reading LHC starts run at 7-TeV collisions.
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.
Science: The first superconductors were discovered in 1911. Half a century passed before physicists came up with a theory that could explain why some compounds had zero resistance at a few degrees above absolute zero. In 1986, researchers discovered complex compounds nicknamed "cuprates" containing copper and oxygen that become superconductors at much higher "critical temperatures"—now as high as 138 kelvin, but couldn't explain how or why they worked.
In the last couple of years, researchers have discovered a new type, four families of iron-based superconductors with distinct crystal structures, that superconduct at temperatures as high at 27 Kelvin. Using tools honed on the cuprates they have made measurements that took decades to achieve in the older materials.
More importantly, although physicists cannot say exactly how the iron-based superconductors work, they have developed a scheme that many say captures the essence of what's going on. "We don't have a full solution yet," says MIT theorist Patrick Lee, "but the situation is better than in the cuprates."
In fact, the emerging portrait of the iron-based superconductors jibes with some theories of the cuprates and seems to undermine more-exotic alternatives. So if physicists are on the right track with the iron-based superconductors, then the cuprates may not be so inscrutable after all.
Physics Today: Evidence for the most massive antinucleus discovered to date has been published by researchers studying high-energy collisions of gold ions at the Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC).
The new antinucleus, discovered at RHIC’s STAR detector (see right), is a negatively charged state of antimatter containing an antiproton, an antineutron, and an anti-Λ particle. It is also the first antinucleus containing an anti-strange quark. The results will be published online by Science Express.
“This experimental discovery may have unprecedented consequences for our view of the world,” commented theoretical physicist Horst Stoecker, vice president of the Helmholtz Association of German National Laboratories. “This antimatter pushes open the door to new dimensions in the nuclear chart—an idea that just a few years ago, would have been viewed as impossible.”
The discovery may help elucidate models of neutron stars and opens up exploration of fundamental asymmetries in the early universe.
New nuclear terrain
All terrestrial nuclei are made of protons and neutrons (which in turn contain only up and down quarks). The standard Periodic Table of Elements is arranged according to the number of protons, which determine each element’s chemical properties. Physicists use a more complex, three-dimensional chart to also convey information on the number of neutrons, which may change in different isotopes of the same element, and a quantum number known as “strangeness,” which depends on the presence of strange quarks (see diagram). Nuclei containing one or more strange quarks are called hypernuclei.
The diagram above is known as the 3-D chart of the nuclides. The familiar Periodic Table arranges the elements according to their atomic number, Z, which determines the chemical properties of each element. Physicists are also concerned with the N axis, which gives the number of neutrons in the nucleus. The third axis represents strangeness, S, which is zero for all naturally occurring matter, but could be non-zero in the core of collapsed stars. Antinuclei lie at negative Z and N in the above chart, and the newly discovered antinucleus (magenta) now extends the 3-D chart into the new region of strange antimatter.
For all ordinary matter, with no strange quarks, the strangeness value is zero and the chart is flat. Hypernuclei appear above the plane of the chart. The new discovery of strange antimatter with an antistrange quark (an antihypernucleus) marks the first entry below the plane.
This study of the new antihypernucleus also yields a valuable sample of normal hypernuclei, and has implications for our understanding of the structure of collapsed stars.
“The strangeness value could be non-zero in the core of collapsed stars,” said Jinhui Chen, one of the lead authors, a postdoctoral researcher at Kent State University and currently a staff scientist at the Shanghai Institute of Applied Physics, “so the present measurements at RHIC will help us distinguish between models that describe these exotic states of matter.”
The findings also pave the way towards exploring violations of fundamental symmetries between matter and antimatter that occurred in the early universe, making possible the very existence of our world.
Collisions at RHIC fleetingly produce conditions that existed a few microseconds after the Big Bang, which scientists think gave birth to the universe some 13.7 billion years ago. In both nucleus-nucleus collisions at RHIC and in the Big Bang, quarks and antiquarks emerge with equal abundance. At RHIC, among the collision fragments that survive to the final state, matter and antimatter are still close to equally abundant, even in the case of the relatively complex antinucleus and its normal-matter partner featured in the present study. In contrast, antimatter appears to be largely absent from the present-day universe.
“Understanding precisely how and why there’s a predominance of matter over antimatter remains a major unsolved problem of physics,” said Brookhaven physicist Zhangbu Xu, another one of the lead authors. “A solution will require measurements of subtle deviations from perfect symmetry between matter and antimatter, and there are good prospects for future antimatter measurements at RHIC to address this key issue.”
In a single collision of gold nuclei at RHIC, many hundreds of particles are emitted most created from the quantum vacuum via the conversion of energy into mass in accordance with Einsteins famous equation E = mc2. The particles leave telltale tracks in the STAR detector (shown here from the end and side). Scientists analyzed about a hundred million collisions to spot the new antinuclei, identified via their characteristic decay into a light isotope of antihelium and a positive pi-meson. Altogether, 70 examples of the new antinucleus were found.
The STAR team has found that the rate at which their heaviest antinucleus is produced is consistent with expectations based on a statistical collection of antiquarks from the soup of quarks and antiquarks generated in RHIC collisions. Extrapolating from this result, the experimenters believe they should be able to discover even heavier antinuclei in upcoming collider running periods. Theoretical physicist Stoecker and his team have predicted that strange nuclei around double the mass of the newly discovered state should be particularly stable.
RHIC’s STAR collaboration is now poised to resume antimatter studies with greatly enhanced capabilities. The scientists expect to increase their data by about a factor of 10 in the next few years.
redOrbit: Unless you're interested in isotopic labeling, neutrons don't figure much into chemistry. Neutral in charge and a bit bigger than a proton, the neutron neither gives an atom its name nor determines much about its reactivity.
But neutrons have some unsung properties that make them useful for investigating matter. Because they are neutral, they can penetrate deeper into a sample than electrons can. Because they have mass and spin, they have a magnetic moment and can probe magnetism. Because they interact with nuclei rather than electron orbitals, they are sensitive to light elements and can even distinguish between hydrogen and deuterium. And they're nondestructive. These features are inspiring researchers to use neutrons to analyze a variety of materials, from coal and complex fluids to cell membranes and membrane proteins and including magnetic materials.
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."
Nature: The finding that the normal phase of an ultracold gas of fermionic atoms in the strongly interacting regime is close to a Fermi liquid isn't quite what theorists expected for these systems.
Science: One of the quests of condensed-matter physics is to discover materials with new types of collective electronic properties, such as the giant magnetoresistance materials now used for memory storage or high-temperature superconductors.
Such "strongly correlated electron" materials challenge our understanding and provide the grist for future technologies.
However, identifying new kinds of electronic behavior is still serendipitous, largely because the materials structures of greatest interest do not crystallize to order.
In Science H. Shishido and associates introduce a systematic approach based on molecular beam epitaxy for the preparation of complex interacting electron materials, thus opening up the possibility of making available many new structures not currently accessible to direct chemical synthesis.
Related link
Tuning the dimensionality of the heavy fermion compound CeIn3
Science: In the natural sciences, x-ray crystallography has clarified how the shapes of proteins and related complexes relate to their cellular function, and x-ray scattering has elucidated the structure and dynamics, mechanical properties, and intermolecular interactions of countless materials.
In Science, H. Cui and coworkers report a new twist in the application of x-ray scattering, where synchrotron x-ray irradiation, in addition to its usual role in probing structure, acts as a reversible switch for self-assembly from a disordered to an ordered state of bundled filaments.
Related link
Spontaneous and x-ray–triggered crystallization at long range in self-assembling filament networks
The Daily Telegraph: A team of scientists from the universities of Bristol, Glasgow, and Southampton have found a way to tie light up in knots.
The light was controlled using holograms specially designed with "knot theory"—a branch of abstract mathematics inspired by twists in shoelaces and rope.
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
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
CDMS group/Physics Today: The Cryogenic Dark Matter Search (CDMS) experiment, located a half mile underground at the Soudan mine in northern Minnesota claims to have seen two events that may be dark matter. The evidence however, is not conclusive, but does limit the interaction range for seeing dark matter, and rules out some theories on how dark matter behaves.
A more detailed story will appear on the Physics Today Update section on the 28 December.
What is dark matter?
Astronomical observations from telescopes, and satellites, and measurements of the cosmic microwave background have led scientists to believe that most of the matter in the universe neither emits nor absorbs light.
This dark matter would have provided the gravitational scaffolding that caused normal matter to coalesce into the galaxies we see today. In particular, scientists think that our own galaxy is embedded within an enormous cloud of dark matter. As our solar system rotates around the galaxy, it moves through this cloud.
Particle physics theories suggest that dark matter may be composed of weakly interacting massive particles (WIMPs). Scientists expect these particles to have masses comparable to, or perhaps heavier than, atomic nuclei.
Although such WIMPs would rarely interact with normal matter, they may occasionally scatter from an atomic nucleus like billiard balls, leaving a small amount of energy that might be detectable under the right conditions.
Detecting WIMPS
The CDMS experiment uses 30 germanium and silicon detectors in an attempt to detect such WIMP scatters.
The detectors are cooled to temperatures very near absolute zero.
Particle interactions in the crystalline detectors deposit energy in the form of heat, and in the form of charges that move in an applied electric field. Special sensors detect these signals, which are then amplified and recorded in computers for later study.
A comparison of the size and relative timing of these two signals can allow the experimenters to distinguish whether the particle that interacted in the crystal was a WIMP or one of the numerous known particles that come from radioactive decays, or from space in the form of cosmic rays.
These background particles must be highly suppressed if we are to see a WIMP signal. Layers of shielding materials, as well as the half-mile of rock above the experiment, are used to limit the background "noise."
New results
The CDMS experiment has been searching for dark matter at Soudan since 2003. Previous data have not yielded evidence for WIMPs, but have provided assurance that the backgrounds have been suppressed to the level where as few as one WIMP interaction per year could have been detected.
The CDMS group is now reporting on a new data set taken in 2007-08, which approximately doubles the sum of all past data sets.
With each new data set, the CDMS group must carefully evaluate the performance of each of the detectors, excluding periods when they were not operating properly.
Detector operation is assessed by frequent exposure to sources of two types of radiation: gamma rays and neutrons.
Gamma rays are the principal source of normal matter background in the experiment.
Neutrons are the only type of normal matter particles that will interact with germanium nuclei in the billiard ball style that WIMPs would, although neutrons frequently scatter in more than one of our detectors.
Those calibration data are carefully studied to see how well a WIMP-like signal (produced by neutrons) can be seen over a background (produced by gamma rays).
The expectation is that no more than one background event would be expected to be visible in the region of the data where WIMPs should appear.
Since background and signal regions overlap somewhat, achievement of this background level required the CDMUS group to throw out roughly 2/3 of the data that might contain WIMPs, because these data would contain too many background events.
All of the data analysis is done without looking at the data region that might contain WIMP events. This standard scientific technique, sometimes referred to as "blinding," is used to avoid the unintentional bias that might lead one to keep events that have some of the characteristics of WIMP interactions but that are really from background sources.
After all of the data selection criteria have been completed, and detailed estimates of background "leakage" into the WIMP signal region are made, the CDMUS group must "open the box" and see if there are any WIMP events present.
In this new data set there are indeed two events seen with characteristics consistent with those expected from WIMPs.
However, there is also a chance that both events could be due to background particles. A strict set of criteria for determine whether a new discovery has been made, in essence that the ratio of signal to background events must be large enough that there is no reasonable doubt.
Typically there must be less than one chance in a thousand of the signal being due to background. In this case, a signal of about 5 events would have met those criteria. The CDMS group estimate that there is about a one in four chance to have seen two backgrounds events, so the CDMS group is not claiming to have discovered WIMPs.
Instead they say that the rate of WIMP interactions with nuclei must be less than a particular value that depends on the mass of the WIMP. The numerical values obtained for these interaction rates from this data set are more stringent than those obtained from previous data for most WIMP masses predicted by theories.
Such upper limits are still quite valuable in eliminating a number of theories that might explain dark matter.
What comes next?
While the same set of detectors could be operated at Soudan for many more years to see if more WIMP events appear, this would not take advantage of new detector developments and would try the patience of even the most stalwart experimenters (not to mention theorists). A better way to increase the sensitivity to WIMPs is to increase the number (or mass) of detectors that might see them, while still maintaining the CDMS group's ability to keep backgrounds under control.
This is precisely what CDMS experimenters (and many other collaborations worldwide) are now in the process of doing. By summer of 2010, the CDMS group hopes to have about three times more germanium nuclei sitting near absolute zero at Soudan, patiently waiting for WIMPs to come along and provide the perfect billiard ball shots that will offer compelling evidence for the direct detection of dark matter in the laboratory.
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."
Related Links
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
Nature News: Rusi Taleyarkhan, of Purdue University, West Lafayette, Indiana, who claimed that he could perform "bubble fusion" in a table-top apparatus has been debarred from receiving federal funding for 28 months, according to the US Office of Naval Research.
Physics Today: Los Alamos National Laboratory has conducted its first-ever double-viewpoint hydrodynamic test of a nuclear weapon component mockup at LANL's Dual Axis Radiographic Hydrodynamic Test (DARHT) facility.
DARHT has been operational for 10 years on one axis, but using a second axis simultaneously is a milestone for the facility.
The test is part of the National Nuclear Security Administration's stockpile stewardship program to continue to maintain the viability of US nuclear weapons without having to resort to underground nuclear tests.
"This is an important development," said Brig. Gen. Garrett Harencak, NNSA principal assistant deputy administrator for military application. "The multiple X-ray images provided by [DARHT] will inform the critical work of our scientists and engineers across the nuclear security enterprise."
"Initial indications show excellent data return," said the hydrodynamic experiments division leader, David Funk. "The baseline experiment captured five time-dependent X-ray images and a variety of data from other diagnostics of pressure, temperature, and timing. This data provides the nation with one of the most rigorous tests of our capability to predict [nuclear] weapons performance."
Conducted inside a specially designed double-walled containment vessel, the test used high explosives to drive an implosion of a duplicate of a W78 nuclear warhead made from non-nuclear surrogate materials. As the mockup is imploding, the DARHT facility fires two electron accelerators positioned at a 90-degree angle from one another to generate high-power x-rays that are used to create multiple images of the imploding device's inner workings, which are then compared with computer predictions.
The DARHT team solved a variety of technical challenges in the months and years leading up to this experiment. "While the first axis of DARHT has been functioning nearly flawlessly for more than 10 years, the second axis is still an operational prototype of the world's longest pulsed electron linear accelerator, so the challenges have been monumental," said Funk. "Just fitting the accelerator in the building had its challenges, leading to the use of a novel material with an exceptionally high magnetic field strength. Using standard materials would have required the accelerator to be five times bigger than it is, and it would not have fit in the building."
Other challenges included designing a cathode injector system that would supply enough electrical current to the accelerator and developing a target that is robust enough to survive four pulses from the extremely high-energy electron beam of the second axis.
"I couldn't be more proud of our team's accomplishments preparing and conducting this first test," said Funk. "The test marks the beginning of what will be a very long operational lifetime for this important diagnostic tool in support of national security."
Nature: Electrical injection and detection of spin-polarized electrons in a silicon chip have now been demonstrated at room temperature, paving the way to the development of low-power semiconductor spintronics circuitry.
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
Nature: The fractional quantum Hall effect (FQHE) is a fascinating form of collective electronic behavior.
It arises when electrons in a strong magnetic field—applied at a right angle to the plane in which the electrons flow—act together to behave like particles with a charge that is a fraction of an electron's charge.
Its observation requires the use of two-dimensional systems virtually free of disorder. This is why, since its discovery by Daniel Tsui and Horst Störmer in 1982—for which they won the 1998 Nobel Physics prize—the effect has been studied in ultrapure semiconductor heterostructures (devices that contain thin layers of one or more semiconductors) grown in an ultrahigh vacuum.
Two papers, one by Xu Du and colleagues and Kirill I. Bolotin and colleagues, show that the FQHE can also be observed in graphene—a one-atom-thick sheet of graphitic carbon, the production of which requires no more sophistication than a common adhesive tape to manually exfoliate graphite in ambient conditions
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Fractional quantum Hall effect and insulating phase of Dirac electrons in graphene
Observation of the fractional quantum Hall effect in graphene
Nature: Materials that combine ferroic properties—such as ferromagnetism and ferroelectricity—are highly desirable, but rare. A new class of multiferroic solids heralds a fresh approach for making such materials.
Multiferroics are attractive candidates for use in electrically controllable microwave elements, magnetic-field sensors and possibly even in spintronics.
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.
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Nature News: Physicists have created a black hole for light that can fit in your coat pocket. Their device, which measures just 22 centimeters across, can suck up microwave light and convert it into heat.
Various: A series of papers in Science and Nature report new results on spin ices and monopoles.
The Nature paper
Spin ices are an exotic class of crystalline solids that are rare, three-dimensional systems in which the magnetic moments (spins) of the ions remain disordered even at the lowest temperatures available writes Shivaji Sondhi in Nature. This means that the geometrical layout of the atoms are such that the norths and souths are never able to align in a satisfactory way and so the magnets continually flip up and down trying to find a stable position says Hannah Delvin in the London Times.
The material has a second property, at regular intervals on the lattice the magnetic fields of individual atoms add up to produce essentially isolated north or south charges, behaving as point-like objects that are the condensed-matter versions of Paul Dirac's theoretical magnetic monopoles—particles that, unlike iron magnets, have a single magnetic pole and hence carry an overall magnetic charge.
Initially, it was not evident that their charge could be measured in a straightforward way. Magnetic monopoles live in a lattice at a moderate density under normal laboratory conditions—not the sort of setting in which you could carry out a magnetic version of Millikan and Fletcher's oil-drop experiment to determine the electric charge of the electron.
But Steve Bramwell of the London Centre for Nanotechnology and colleagues in Nature report a measurement of the magnetic charge of the monopoles in spin ice that is in surprisingly good agreement with the theoretical prediction.
"It is not often in the field of physics you get the chance to ask, ‘How do you measure something?’, and then go on to prove a theory unequivocally," said Bramwell to Delvin. "This is a very important step to establish that magnetic charge can flow like electric charge."
The Science papers
In Science, two groups also report measurements from neutron-scattering experiments showing that the low-energy excitations in spin ices are reminiscent of magnetic monopoles writes Michel J. P. Gingras.
These dissociated north and south poles diffuse away from each other in these oxides and leave behind a "Dirac string" of reversed spins that can be seen as patterns in the intensity of scattered neutrons.
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Discovery of ‘magnetricity’ marks important advance in physics London Times
Measurement of the charge and current of magnetic monopoles in spin ice Nature
Observing Monopoles in a Magnetic Analog of Ice Science
Magnetic Coulomb Phase in the Spin Ice Ho2Ti2O7 Science
Dirac Strings and Magnetic Monopoles in the Spin Ice Dy2Ti2 Science
Science: Ferromagnets, such as those made of iron or nickel, are called itinerant because the electrons whose spins aligned to create the magnetic state are extended and are the same as the ones responsible for conduction. Ferromagnetism was a mystery for classical physics, and its explanation in terms of spin, exchange interactions, and repulsions between identical particles was a triumph of early quantum mechanics.
However, it proved difficult to apply these early models to real ferromagnets in a quantitative way, both because the simple models neglect important features relevant in real materials and because theoretical tools to properly treat the strong correlation problem have only recently been developed. Fortunately, the simple models studied in the early days of quantum mechanics can also be applied to fermions other than electrons. In Science a paper discusses new evidence for an analog of ferromagnetism in an ultracold gas of neutral lithium-6 atoms. When repulsive interactions between these freely moving particles are sufficiently strong, a transition to ferromagnetic ordering is seen.
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Itinerant Ferromagnetism in a fermi gas of ultracold atoms
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."
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.
Science: As they prepare to restart the Large Hadron Collider, accelerator physicists are confident that, instead of suffering a second catastrophic breakdown, the world's largest atom smasher will perform to the standards set by its predecessors—and give them lots of smaller headaches to struggle with.
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CERN confirms that LHC will run at 3.5 TeV
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Nature: Certain insulators have conducting surfaces that arise from subtle chemical properties of the bulk material. The latest experiments suggest that such surfaces may compete with graphene in electronic applications.
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Topological surface states protected from backscattering by chiral spin texture
A tunable topological insulator in the spin helical Dirac transport regime
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.
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Holographic Ghost Imaging and the Violation of a Bell Inequality. Physical Review Letters, in press
Physics Today: CERN's Director General, Rolf Heuer has confirmed that the Large Hadron Collider will run at 3.5 TeV leading to collisions at 7 TeV when it is turned on in November.
"We've selected 3.5 TeV to start," said Heuer, "because it allows the LHC operators to gain experience of running the machine safely while opening up a new discovery region for the experiments."
The lower energies are because not all the magnets appear to be working at full strength, and the copper stabilizer connections cannot be run at the higher energies.
Last year the LHC suffered a critical failure when one of the 10,000 high-current superconducting electrical connections failed. CERN has been cooling down and testing various sectors of the collider in order to track down the bad connectors.
The tests on the final two sectors concluded last week and have revealed no more major problems. This means that no more repairs are necessary for safe running this year and next.
"The LHC is a much better understood machine than it was a year ago," said Heuer. "We can look forward with confidence and excitement to a good run through the winter and into next year."
The procedure for the 2009 start-up will be to inject and capture beams in each direction, take collision data for a few shifts at the injection energy, and then commission the ramp to higher energy.
The first high-energy data should be collected in December after the first beam of 2009 is injected. The LHC will run at 3.5 TeV per beam until a significant data sample has been collected and the operations team has gained experience in running the machine.
Gradually the machine will be raised up towards 5 TeV per beam. At the end of 2010, the LHC will be run with lead ions for the first time. After that, the LHC will shut down and work will begin on moving the machine towards 7 TeV per beam.
Science News: A macromolecule that was accidentally discovered when scientists left stuff sitting on a lab bench seems to soak up atmospheric carbon dioxide.
The original find was made by a research team led by chemists at the University of Southampton in England. They were trying to design and create molecules that could capture negatively charged ions, such as chlorides and phosphates, on the surfaces of bioengineered cells.
In one experiment, the researchers set aside an alkaline solution of various organic substances to evaporate, says geochemist John A. Tossell, author of the new study. When analyzing the crystals that formed, the team found that the organic macromolecule that made up the crystal unexpectedly contained carbonates, which form in solutions containing carbon dioxide.
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Nature: A crystal can grow only if all of its atomic or molecular building blocks fit into the periodic lattice. This is true even for colloidal crystals, which form through the ordered self-assembly of micrometer-sized particles. The requirement for periodicity puts stringent constraints on the variation in the size of particles that can be incorporated into a given colloidal crystalline lattice.
But reporting in Angewandte Chemie, Ashlee St. John Iyer and L. Andrew Lyon show that crystals made of microgel particles are much more tolerant of particle size variations than was expected. This surprising feature might have practical implications for the design of ordered colloidal materials.
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Payne Laboratory
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.
Nature: Physicists often state that nuclear shell structure—the way in which protons and neutrons are arranged within a nucleus—is the cornerstone of any satisfactory description of an atomic nucleus. But over the past decade it has become apparent that the exact number of particles required to fill a particular shell is not as fixed as was once thought. The results of two experiments, one by Kanungo et al. reported in Physical Review Letters, and the other by Hoffman et al. in Physics Letters B, add significantly to the discussion. They demonstrate that 24O, the oxygen isotope with proton number Z = 8 and neutron number N = 16, is a doubly magic nucleus. This result is all the more surprising because 24O is also the heaviest oxygen isotope to exist.
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One-neutron removal measurement reveals 24O as a new doubly magic nucleus
Evidence for a doubly magic 24O
The Economist: A few years ago Yadong Yin was experimenting with tiny beads that changed color when a magnetic field was applied to them. This was interesting but there was no obvious way to turn them into a product
Now Yin and his colleagues at the University of California, Riverside, have come up with possible applications that range from a new type of paint to lipsticks and giant advertising billboards.
Yin’s beads are magnetochromatic microspheres. They are made from tiny blobs of polymer that contain particles of iron oxide. The structure of these particles changes in a magnetic field in a way that produces “interference” colors when light is shone on them.
It is the rearrangement of the particles’ microstructures that produces the pertinent detail.
The new research appears in the 15 June Journal of the American Chemical Society.
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.
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CNET News: IBM already had technology that could measure extremely subtle forces among atoms, but a nanotechnology development at the company's Zurich Research Laboratory shows a new level of sensitivity: the ability to distinguish positively charged atoms from those that are neutral or negatively charged.
The atomic force microscope maps what's below by detecting subtle changes in forces of attraction.
Researchers at the Zurich lab, along with colleagues at the University of Regensburg and Utrecht University, used an atomic force microscope (AFM) with a tuning-fork detector arrangement on the tip of its probe to distinguish among gold atoms that were positively charged, neutral, or negatively charged. The researchers describe their approach in the June 12 issue of Science.
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IBM scientists directly measure charge states of atoms using an atomic force microscope
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Science: The ability to observe individual chemical reactions in real time is reshaping our understanding of molecular processes, revealing subtleties previously hidden in ensemble averages. For example, single-molecule fluorescence detection methods have revolutionized optical microscopy and in situ studies of chemical and biological systems. Liquid cell in situ transmission electron microscopy (TEM) is poised to write a new chapter in the solution synthesis and processing of materials. Haimei Zheng and colleagues use a TEM liquid cell that allows liquids to be examined within the vacuum environment of a TEM in an elegant experiment that uncovers dynamic processes in the growth of platinum (Pt) nanocrystals.
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Observation of Single Colloidal Platinum Nanocrystal Growth Trajectories
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.
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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.
ScienceNOW: Researchers have built a nanoscale device that vibrates when struck by incoming laser light. The contraption, which is sensitive to the energy of a single photon, could speed the development of new optical communications systems. It could also help scientists probe some of the fundamental properties of matter with greater precision
Science: Superfluid helium is best known for its ability to flow without resistance. Superfluids also differ from ordinary fluids in that they fail to respond to a slow steady rotation says John Saunders in Science magazine. The atoms in a superfluid are in the same quantum state, so they move coherently and cannot gradually "spin up," as does water in a rotated container. An intriguing question is whether a supersolid—formed by applying pressure to a superfluid—could combine these remarkable properties, quantum coherence and dissipationless mass flow of atoms, in a solid that still has structural order and rigidity.
In an ordinary classical crystal, all atomic motion is frozen out at absolute zero, but solid helium-4 is a quantum solid; each atom is highly delocalized in a quantum probability cloud around its equilibrium position, and as a result, atoms on neighboring sites can exchange positions and move through the solid. In 2004, Kim and Chan (5) claimed to have observed supersolidity in solid helium-4. This discovery was followed by experimental and theoretical studies suggesting that disordered glassy solids play a key role in creating the putative super-solid state.
Two reports in last week's Science journal address the origin and effects of this disorder. Hunt et al. report their observation of the onset of remarkable ultraslow dynamics on cooling samples of solid helium, which constitutes new evidence for glass-like behavior. They reveal a subtle interplay between this glassiness and the observed supersolid-like mechanical responses. Philip Anderson argues that the supersolid will still occur in a pristine crystal, but coupling to disordered regions near dislocations enhances the supersolid response. His bold hypothesis is that every solid composed of bosons will have a supersolid ground state.
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Nature: The handedness of chiral molecules can be probed spectroscopically, but acquiring data can take hours, which is a problem for time-resolved studies. The latest method records such data in a flash.
Nature News: Contrary to some expectations in the world of nuclear physics, researchers have found that a radioactive nucleus of sulphur oscillates between two different shapes, sometimes appearing like a sphere and other times like an American football. The result, reported this month by researchers in France, is causing nuclear physicists to rethink prevailing theories about what makes some nuclei stable and others prone to splitting apart.
Science: Entanglement, a seemingly impossible link between distant particles, is key to physicists' plans for revolutionary quantum computers and uncrackable quantum communications systems. Creating entangled pairs of light particles, or photons, is a delicate business. Now, physicists from Japan and the United Kingdom have found a way to do it by simply passing ordinary photons through a novel optical filter.
"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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Nature: The conventional approach to flipping electron spins in a semiconductor requires an external alternating field. It seems that the same job can be accomplished without external excitation of any kind.
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Nature News: The fundamental asymmetry in the laws of physics called charge-parity violation is tiny, yet it looms large enough in physics to have led to Nobel prizes on three occasions. A persistent puzzle is why the asymmetry is so small -- some theories imply that it could, and perhaps should, be much bigger. Now, research is bolstering a previous suggestion that the smallness is not a mystery but rather an inevitable consequence of another basic fact in physics: that the three known families of quarks have the masses that they do.
New Scientist: Next month Fabiola Gianotti takes over as head of ATLAS at the Large Hadron Collider at CERN in Switzerland. The largest experiment of its kind, it could answer some of the mysteries of the universe. She talks to Anil Ananthaswamy about dark matter and deep truths
Nature: In most solids, electrons behave much like particles of matter: they have a mass, and they speed up and slow down in response to forces. But in graphene — the single-atom-thick sheet of carbon that constitutes the basic building block of graphite — electrons move as if they have no mass1, 2, and so behave more like photons. In other words, although electrons in graphene can change their momentum and energy, they cannot speed up or slow down. One would therefore intuitively think that electron flow (electrical current) in graphene could never be completely blocked. But reporting in Science, Elias and colleagues show that, when graphene reacts with a small amount of hydrogen, its electrons become stuck and the carbon sheet becomes an insulator.
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Science:Every once in a while, experiments are reported that apply existing tools to apparently well-understood scientific concepts and come up with tantalizing, novel results. In Science magazine, such a case is beautifully demonstrated by Weismann and colleagues. They use scanning tunneling microscopy (STM), a standard surface science technique, to visualize electron flow in the bulk of a piece of copper.
Primarily based on its atomic resolution imaging capability, the STM has had phenomenal success in the field of surface science. How can a truly surface-sensitive technique be used to measure a bulk property? The key trick applied by Weismann et al. is to exploit the wave nature of the electrons in copper and study their interference patterns on the surface caused by scattering centers in the bulk of the material. Their technique opens the door to a real-space investigation of electron propagation in materials and to the scattering of electrons at defects well below the surface.
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BBC: Europe's particle physics lab, Cern, is losing ground rapidly in the race to discover the elusive Higgs boson, or "God particle", its US rival claims
Science: Two years ago, physicists blurred the distinction between science and fiction by producing a shell-like "invisibility cloak" that made both itself and an object inside it undetectable-- albeit when viewed with microwaves of a specific frequency. Now, a team from Hong Kong has gone one better with a theoretical scheme for an "invisibility umbrella" that can make both itself and an object placed beside it disappear
Science News: A flat, two-dimensional flow of electric current has long been thought essential to the secret of how high-temperature superconductors work. But new research shows that an iron-based superconductor allows current to flow in three dimensions.
Science: Officials at CERN, the European particle physics lab near Geneva, Switzerland, issued a four-page report last week tersely describing how they plan to get the 27-kilometer-long Large Hadron Collider (LHC), the world's biggest particle smasher, working again after its 19 September breakdown. Although the report doesn't mention errors in design, the list of fixes does point to flaws, including one that some physicists say cannot be completely eliminated. "There are some questions about the design, and they are fixing some of them and some of them cannot be fixed," says Peter Limon, an accelerator physicist at Fermi National Accelerator Laboratory in Batavia, Illinois.
Science: String theory was first formulated in the early 1970s with the objective of explaining aspects of the strong interactions of particle physics. The strings were literally strings of energy that bound together a quark and an antiquark to form subatomic particles called mesons. This original string theory, however, was ultimately unsuccessful and it was only consistent in 10 dimensions of spacetime. String theory was then reincarnated as a unifying theory of quantum gravity, with breakthroughs in the mid-1980s ushering this grander version into the mainstream. A recent turn of events is leading a growing fraction of string theory research back to studying specific laboratory systems, including those of condensed-matter physics.
Science: Why do some solids conduct electricity like a metal, and others act like insulators? Quantum mechanics has provided some relatively simple (and quite successful) models for electron conductivity, but the underlying physics is often complex, because electrons interact with each other through Coulomb forces and because real materials are not perfectly ordered. In the December 5 issue of Science, Schneider et al. address the microscopic distinction between a conductor and an insulator by examining the conducting properties of repulsively interacting 40K atoms, which, like electrons, are fermions--they have half-integer spin and obey the Pauli Exclusion Principle, which allows only one fermion to occupy a quantum state. By placing ultracold 40K atoms in an artificial crystal held in place through optical fields, they can manipulate the energy scales of the system so that it varies all the way from a metallic state to different kinds of insulating phases.
Nature: Electric fields offer an innovative means of controlling condensed-matter systems. The approach has been applied to nanoscale oxide interfaces, for studying the physics of two-dimensional superconductors.
Nature: Free-electron lasers could produce X-rays intense enough to make atomic-resolution movies. Initial designs are kilometres long, but a prototype working in the ultraviolet points a way to shorter machines.
Nature: Metamaterials are the key to perfect lenses, 'invisibility' cloaks and slow and stored broadband light. A three-dimensional optical metamaterial with a negative refractive index has now been created
Nature: Conductors and semiconductors usually behave like conduits for fluids of electrons. But sometimes the electrons' spins conspire to produce unconventional behaviors that can be turned off and on with magnets.
Science: The self-assembly of block copolymers into nanoscale features is potentially attractive as a means for patterning media in microelectronic applications. This new route to nanopatterning is gaining interest as optical lithography, the current engine of the semiconductor industry, begins to approach intrinsic technological limits while demand for higher-density features for improved data storage and computing speed continues to grow. These applications require not only regularly sized nanoscale features but also a degree of perfection of order and registry relative to other components, which have so far been elusive in self-assembled systems. In this week's issue of Science, two papers ( Graphoepitaxy of Self-Assembled Block Copolymers on Two-Dimensional Periodic Patterned Templates and Density Multiplication and Improved Lithography by Directed Block Copolymer Assembly) describe how block copolymers in conjunction with coarse templates are used to create nanoscale structures with an unprecedented level of control.
Science: Metals are solids in which conduction electrons remain mobile even at absolute zero temperature. In a semimetal, the concentration of such mobile electrons is extremely low. Whereas in a typical metal, say copper, there is roughly one itinerant electron per atom, in bismuth, the archetypal semimetal, 100,000 atoms share a single mobile electron. On the July 25 issue of Science, Li et al. report that in the presence of a strong magnetic field, this dilute electron gas orders in a way never observed in any other material.
Nature: Different material options for high-temperature superconductivity— conduction of electricity with little or no resistance at 'practical' temperatures — have arrived. Iron compounds are the latest thing.
Nature News: Observations of the cosmic microwave background might deal blow to theory.
Science: Do iron-and-arsenic superconductors work the same way as the older, inscrutable copper-and-oxygen compounds? Early evidence points both ways.
Related Physics Today article
New family of quaternary iron-based compounds superconducts at tens of kelvin (May 2008)
Nature: There's a long wish list for a workable quantum computer: a viable system must be fast, compact and stable. The first integrated optical quantum logic circuits are a step in the right direction.
Nature: In the quest for a quantum computer, no obstacle is more formidable than decoherence — the 'collapse' of an information-encoding quantum wavefunction when it couples to its surroundings. We pressingly need to understand what causes it, how it works and how to get rid of it. Bertaina and colleagues have passed a milestone on that road. They report the first observation of Rabi oscillations, a signature of coherent spin dynamics, in a magnetic molecule of a kind envisaged as the basic physical carrier of a 'qubit' of quantum information in a quantum computer. Perhaps more importantly, they have also succeeded in pinpointing the sources of decoherence in their system, and so taken the first step towards eliminating them.
NPR: Introductory electronics classes focus on circuit diagrams involving different combinations of resistors, capacitors and inductors. Now, researchers say that they have discovered a fourth fundamental passive circuit element — one that fills in a gap in the basic equations that describe the relationships between voltage, current and magnetic flux.
The possibility of such a circuit element, known as the "memristor," was first described in 1971, but no one was able to find a device with the properties of that missing element. Now, a group of scientists at HP Labs has found that in nanoscale materials, the "memristance" property becomes easier to see.
The finding could lead to lower power, instant-on computers, as well as novel types of circuitry. HP Senior Fellow Stanley Williams, one of the discoverers of the modern memristor, talks about the find and its potential applications.
The possibility of such a circuit element, known as the "memristor," was first described in 1971, but no one was able to find a device with the properties of that missing element. Now, a group of scientists at HP Labs has found that in nanoscale materials, the "memristance" property becomes easier to see.
The finding could lead to lower power, instant-on computers, as well as novel types of circuitry. HP Senior Fellow Stanley Williams, one of the discoverers of the modern memristor, talks about the find and its potential applications.
Nature News: Could super-heavy elements be lurking in plain sight? One group of physicists says that they are, and claims to have seen the heaviest element yet found hiding amongst thorium atoms.
Some theories predict that some super-heavy elements might be unusually stable, thanks to a 'magic' number of protons and neutrons, and so could be lying around in nature. Several groups are now engaged in searches for them. If confirmed, this would be the first report of finding one.
But the team's claims, which are not peer-reviewed, are being heavily criticised by other physicists, who fear that their technique is flawed. "I have grave doubts," says Rolf-Dietmar Herzberg, a nuclear physicist at the University of Liverpool, UK.
Some theories predict that some super-heavy elements might be unusually stable, thanks to a 'magic' number of protons and neutrons, and so could be lying around in nature. Several groups are now engaged in searches for them. If confirmed, this would be the first report of finding one.
But the team's claims, which are not peer-reviewed, are being heavily criticised by other physicists, who fear that their technique is flawed. "I have grave doubts," says Rolf-Dietmar Herzberg, a nuclear physicist at the University of Liverpool, UK.
Science: The rise of nanotechnology is garnering much attention for its ability to construct objects with individual atoms and molecules, at a scale roughly a billion times smaller than the objects we encounter in our everyday lives. In parallel to nanotechnology's often astonishing achievements, scientists have started to build a capacity to do useful work on an even more minute scale. During the past decade, chemists and physicists have begun a fabrication process at the scale of the atomic nuclei. It is an emergent means of producing, in sufficient quantities, "designer" atomic nuclei, which are new, rare isotopes with unusual numbers of neutrons or protons, or unusual decay modes (1). There are several reasons why a latent demand exists within the scientific community for new isotopes. One is that the properties of particular isotopes often hold the key to understanding some aspect of nuclear science. Another is that the rate of certain nuclear reactions involving rare isotopes can be important for modeling astronomical objects. Finally, the pursuit of ever more exotic isotopes sometimes advances basic understanding of the nuclear landscape, along with unexpected areas of application.
csmonitor.com: Scientists around the world are scrambling to unlock the secrets behind a new group of materials that act as autobahns for electricity – conducting current with virtually no wasteful resistance.
The discovery establishes a third major group of so-called high-temperature superconductors – a broad category that scientists first uncovered in 1986. Such materials hold the promise of making everything from computers to electric motors far more efficient, as scientists boost the temperature frontiers at which the materials work.
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New family of quaternary iron-based compounds superconducts at tens of kelvin May 2008
Nature: After 20 years of hard labour, squeezed states — light and matter whose quantum fluctuations have been arduously suppressed below standard levels of quantum noise — are coming of age and are ripe for application.
Nature News: How does our classical world emerge from the counterintuitive principles of quantum theory? Can we even be sure that the world doesn't 'go quantum' when no one is watching? Philip Ball talks to the theorists and experimentalists trying to find out
Nature News: Some experts think that a quantum computation could be plaited like a skein of string. And now they may have found the sorts of string they need, finds Liesbeth Venema.
When Alexei Kitaev published a preprint suggesting that the topological properties of quasiparticles, moving around each other and behaving as anyons, could be used as the basis for a new form of error-proof quantum computing, it seemed absurd.
“I laughed when I first read it,” recalls Nick Bonesteel, a theoretical physicist at Florida State University in Tallahassee. And there may still be some people laughing today — but at least a few of them are doing so with excited anticipation.
Related Physics Today material
Devices Based on the Fractional Quantum Hall Effect May Fulfill the Promise of Quantum Computing (October 2005)
Nature: A particle-like object with a quarter of an electron's charge is the latest find in a hotbed of quantum-physical experimentation, the fractional quantum Hall fluid. Its significance is more than esoteric.
The Post Chronicle: Physicists Create Superinsulators by Staff U.S. and European scientists have discovered a fundamental state of matter that they say opens new directions of inquiry in condensed matter physics. via The Post Chronicle
Nature: As the great quantum physicist Werner Heisenberg — he of the uncertainty principle — made plain, in quantum mechanics, separation of the observer from the phenomenon to be observed is not possible. But in fact, the strange idea that consciousness, intelligence and the act of observation are intertwined with physical phenomena predates Heisenberg. Specifically, James Clerk Maxwell famously introduced into his studies of thermodynamics "a being whose faculties are so sharpened that he can follow every molecule in its course", such that it could identify and siphon off the hotter (faster) molecules in a gas. 'Maxwell's demon' would thus be able to extract useful work from the system, while heat is in effect transferred from a cooler to a hotter region — in clear breach of the normal direction of heat flow from hotter to cooler encapsulated in the second law of thermodynamics.
In this week's Nature, Erez and others provide a neat link between these physical curiosities, by suggesting a way to use the quantum measurement process to control a system's thermodynamics, in the spirit of Maxwell's demon. At the heart of their concept is the quantum-physical equivalent of the old adage 'a watched pot never boils'. This is the quantum Zeno effect, which states that, if you measure a quantum system often enough, it will never be able to change its state, and so will not evolve at all.
Science: Can ultracold, highly pressurized solid helium flow like the thinnest possible liquid? For 4 years, physicists have debated that question. Now, preliminary data from Robert Hallock of the University of Massachusetts (UMass), Amherst, and his team provide the most direct evidence yet for such flow.
"It's a very, very clever experiment," says Moses Chan of Pennsylvania State University in State College. But all agree it hasn't solved the mystery of solid helium.
Physics Update: A new study shows how a region of space could be rendered invisible to matter waves. In recent years the possibility of optical cloaking has become a hot topic (e.g., Science, 8 Sept 2006). Even cloaking with sound waves has been proposed. Now physicists in Xiang Zhang’s group at the University of California, Berkeley, are trying to extend the cloaking idea to atom waves (chilled atoms whose quantum wavelike properties are more important than their particle-like properties) moving through a medium.
The “medium” in question here is a concentric optical lattice, generated by standing electromagnetic waves with spatially controlled amplitudes and phases. Cloaking of an object bathed in light works by modulating the effective mass and potential of atom waves traversing the shell surrounding the object. The shell is analogous to the metamaterials (tailored materials often consisting of arrays of tiny rods and ring-shaped metal structures) used in the optical case.
One of the Berkeley researchers, Shuang Zhang says that the atom-wave equivalent of an index of refraction would be the modulation of the effective atomic mass inside the optical lattice. Zhang says that apart from cloaking, the creation of a metamaterial for atom waves might also help in focusing atom waves into tiny spot (super-lensing) or for steering particle beams at will. (Zhang et al., Physical Review Letters, 28 March 2008.
Nature: An unexpected imbalance in how particles containing the heaviest quarks decay might reveal exotic influences — and perhaps help to explain why matter, rather than antimatter, dominates the Universe.
Related Link
Difference in direct charge-parity violation between charged and neutral B meson decays (Nature)
University of Florida news: Confirming a decades-old prediction, the physicists with the CLEO collaboration say they observed a rare and extremely short-lived subatomic particle with the unusual name of “charmed-strange meson” decay into a proton and anti-neutron.
Detection of the event, which the collaboration made public Sunday, was attributed to John Yelton, a physicist at the University of Florida, one of many institutions that are part of the CLEO collaboration.
“It’s the sort of thing that, for many years, people have known should happen,” Yelton said. “What we have done is show that it does, and how often.”
Yelton said the latest result shows there remains much to be learned from collisions at lower energy in lower energy colliders. “It highlights the fact that there is still physics to be done at lower energy accelerators,” he said.
The CLEO collaboration has also submitted a paper on the discovery to the journal Physics Review Letters.
New York Times: IBM scientists have used the tuning fork in the atomic force microscope, which measures the interaction between the tip and the atom, to calculate the force needed to nudge one atom. About one-130-millionth of an ounce of force pushes a cobalt atom across a smooth, flat piece of platinum. Pushing the same atom along a copper surface is easier, just one-1,600-millionth of an ounce of force
Nova: In preparation for the launch of NPR's new series, absolute zero, Peter Tyson asks a number of physicists if you can't get colder than 0 on the Kelvin scale, is there a corresponding maximum possible temperature?
New Scientist: A paper in Nature Physics suggests that a desktop synchrotron particle accelerator could soon be able to freeze-frame the frenetic motion of atoms and molecules. An international team of physicists led by Dino Jaroszynski of Strathclyde University in Scotland have built a prototype light source, which they claim can be upgraded to produce intense, ultra-short pulses of X-rays. Synchrotrons are in great demand because their intense X-ray beams have so many uses, from analysing biological molecules to etching electronic components and seeing inside microscopic fossils.
Nature: The atoms and bonds that make up complex solids can be identified chemically — a feat made possible by cleverly combining spectroscopic and structural information conveyed by electrons scattered through a thin sample.
Science: The often dramatic effects of particle irradiation on the properties of materials have been recognized and studied for over 60 years. These effects can be detrimental (as in structural materials degradation in nuclear reactors) or beneficial (as in the ion beam processing of semiconductors for the microelectronics industry). However, the microscopic processes that underlie these effects are not entirely understood, limiting researchers' ability to predict the consequences of irradiation. The reports in this week's issue of Science highlight the limits of knowledge about nanometer-sized dislocation loops in materials. The results should stimulate additional research to better understand these phenomena and to use the unique diffusion behavior to pattern materials at the nanoscale.
Science: The often dramatic effects of particle irradiation on the properties of materials have been recognized and studied for over 60 years. These effects can be detrimental (as in structural materials degradation in nuclear reactors) or beneficial (as in the ion beam processing of semiconductors for the microelectronics industry). However, the microscopic processes that underlie these effects are not entirely understood, limiting researchers' ability to predict the consequences of irradiation. The reports in this week's issue of Science highlight the limits of knowledge about nanometer-sized dislocation loops in materials. The results should stimulate additional research to better understand these phenomena and to use the unique diffusion behavior to pattern materials at the nanoscale.
Nature news: Atoms can be more overweight than we thought, a team of scientists in the United States has discovered.
They have sent atoms crashing into one another in a particle accelerator to create bloated versions of the elements aluminium and magnesium. The new, artificial forms of these metals have many more neutrons in their atomic nuclei than do the everyday versions1
Nature: The behaviour of ferromagnetic and ferroelectric materials in a magnetic or electric field makes them easy to spot. But for their more recently discovered counterpart, ferrotoroidic materials, things become complex.
Various:
Albert Fert of the Université Paris-Sud, Orsay, France and Peter Grünberg of the Forschungszentrum Jülich, Germany have won the 2007 Nobel Prize in physics for the discovery of giant magnetoresistance, or GMR for short. GMR is the process whereby a weak magnetic field, such as that of an oriented domain on the surface of a computer hard drive can, when the proper read head is brought nearby, trigger a large change in electrical resistance, thus “reading” the data vested in the magnetic orientation. This is the heart of modern hard drive technology and makes possible the immense hard-drive data storage industry. Earlier this year the two physicists won the Wolf Prize for the same research.
Albert Fert of the Université Paris-Sud, Orsay, France and Peter Grünberg of the Forschungszentrum Jülich, Germany have won the 2007 Nobel Prize in physics for the discovery of giant magnetoresistance, or GMR for short. GMR is the process whereby a weak magnetic field, such as that of an oriented domain on the surface of a computer hard drive can, when the proper read head is brought nearby, trigger a large change in electrical resistance, thus “reading” the data vested in the magnetic orientation. This is the heart of modern hard drive technology and makes possible the immense hard-drive data storage industry. Earlier this year the two physicists won the Wolf Prize for the same research.
Fert and Gruenberg helped pioneer the making of semiconductor stacks consisting of alternating thin layers of magnetic and non-magnetic atoms needed to produce the GMR effect. GMR is a prominent example of how quantum effects (a large electrical response to a tiny magnetic input) come about through confinement (the atomic layers being so thin.); that is, atoms interact differently with each other when they are confined to a tiny volume or a thin plane.
All these magnetic interactions involve the spin of an electron. Spin is a quantum attribute that shouldn’t be associated too closely in the mind with the electron literally spinning (in the way that a top spins). Still more innovative technology can be expected through quantum effects depending on electrons’ spin. Most of the electronics industry is based on manipulating the charges of electrons moving through circuits. But the electrons’ spins might also be exploited to gain new control over data storage and manipulation. Spintronics is the general name for this branch of electronics.
Related Physics Today articles
Layered Magnetic Structures: History, Highlights, Applications, May 2001, page 31
Basic Research in the Information Technology Industry, Jul 2003
Magnetic Semiconductors Enable Efficient Electrical Spin Injection, April 2000, page 21
Physics Today, April 1995 (available November 1)
Related web sites
2007 Nobel Prize site
Wolf Prize announcement
Peter Gruenberg
Recent papers by Fert and Gruenberg
Related news stories
Magnetic Effect Nets a Nobel, Science
Physics of Hard Drives Wins Nobel, New York Times
Magnetic Effect Nets a Nobel, Science
Reuters
Physics Nobel Goes to German, Frenchman, Wired News
Disk technology takes Nobel Prize, BBC
Europeans Win Nobel Prize for Physics, NPR
A little magnetism wins physics Nobel, The Australian
Nature: Well-established models of nuclei describe properties such as shells and magic numbers. But how do these predictions stand up to scrutiny for exotic, unstable nuclei? Pretty well, according to the latest study.
Reuters: Imagine cramming 30,000 full-length movies into a gadget the size of an iPod.
Scientists at IBM said on Thursday they had moved closer to such a feat by learning how to steer single atoms in a way that could create building blocks for ultra-tiny storage devices.
Houston Chronicle: The $1.4 billion Spallation Neutron Source facility, though still powering up, has established a new mark as the world's most powerful accelerator-based source of neutrons for scientific research.
The Oak Ridge National Laboratory announced Thursday that the SNS's neutron beam reached 183 kilowatts on Aug. 11, surpassing the 163-kilowatt record held by the ISIS facility at Rutherford Appleton Laboratory near Oxford, England.
Although the capacity of the ISIS facility is being doubled, Oak Ridge officials said their accelerator is designed to produce up to 10 times more neutrons than now.
Nature: In order to form a glass by cooling a liquid, the normal process of solid crystallization must be bypassed. Achieving that for a pure metal had seemed impossible — until pressure was applied to liquid germanium
AZoNano.com: Northeastern University Physics professor Sergey V. Kravchenko along with colleagues Svetlana Anissimova (Northeastern University), A Punnoose (City College if the City University of New York), AM Finkelstein (Weizmann Institute of Science, Israel) and TM Klapwijk (Delft University of Technology, Netherlands), has published an important new paper in the August issue of Nature Physics which answers a long standing question in the field of condensed matter physics.
Science: More than 20 years after the discovery of cuprate superconductors, physicists do not agree on what mechanism causes the loss of electrical resistance at temperatures as high as 160 K (known as Tc, the transition temperature). They do agree that electron pairs are crucial because they can form a condensate that flows without resistance, but the interaction that causes the pairs to form is disputed. Philip W. Andersen suggests in this week's Science that the bosonic glue most physicists believe is needed to explain the superconducting behavior is folklore rather than the result of scientific logic.
Nature: For most of its existence, a superfluid droplet leads an essentially innocuous, classical life. But intense scrutiny reveals that the birth of such droplets is a turbulent and unpredictable quantum affair.
Nature: The spins of a layer of manganese atoms on a tungsten surface form a spiral pattern with a unique turning sense. Such 'chiral magnetic order' might exist in other, similar contexts, and could have many useful applications.
Science: In quantum physics, decoherence is a catch-all term that usually implies degradation of the purity of a quantum state. Over the past few decades it has been used as a guide to understand the loss of the two-body coherence called entanglement, which is an intrinsically quantum effect. In this context, it is relevant to fundamental questions such as: Why is the world mostly classical when we believe quantum theory provides all of the governing principles? The answer lies in the critical role of "largeness"; simply put, larger bodies lose coherence more quickly. This is the essential ingredient in producing nearly instantaneous decay of entanglement between two large bodies or between a large body and a small one. The role of largeness is seen when decoherence occurs increasingly faster with the size of the environment. Preservation of coherence is important in maintaining steady behavior of quantum systems whose coordinated action is critical, for example, among the working units of quantum computers when they become available.
A small body (spin, photon, atom, exciton, quantum dot, Cooper pair, etc.), on the other hand, can continue to behave as a quantum mechanical unit, even if not macroscopically entangled. A topic that remains open in almost all decoherence discussions, however, is the preservation or destruction of two-body quantum coherence when both bodies are small. For example, it has been predicted only recently that the one-body and two-body responses to a noisy environment can follow surprisingly different pathways to complete decoherence. Experimental entry into this new domain is needed, and impressive results are now reported on page 579 of this week's Science magazine. The researchers have devised an elegantly clean way to check and to confirm the existence of so-called "entanglement sudden death," a two-body disentanglement that is novel among known relaxation effects because it has no lifetime in any usual sense--that is, entanglement terminates completely after a finite interval, without a smoothly diminishing long-time tail.
Science: Like a prisoner trapped behind the wall of a fortress, an electron faces a huge barrier in escaping the confines of an atom. Yet when hit by a burst of intense light, it can set itself free in just a few hundred attoseconds (10-18 s), thanks to a quantum-mechanical phenomenon known as tunneling. In essence, it seeps through the barrier--the binding energy that normally holds it in place. Now, for the first time, scientists have seen this blindingly fast escape act happen in real time.
News@Nature: A team of European physicists led by Anton Zeilinger of the University of Vienna, has successfully transmitted a secure quantum 'key' between two of the Canary Islands, opening the possibility of long-distance, wireless quantum cryptography.
Science: X-ray free-electron lasers promise beams that are vastly brighter and with higher energy and shorter pulses than today's scientific workhorse: synchrotron x-rays. These "hard" x-ray wavelengths—down to 0.1 nanometer—promise to reveal the structure of proteins that have eluded other techniques and nanometer-scale features in materials. Pulses as short as 100 femtoseconds or less will act as strobes to produce movies of molecular bonds breaking and forming in chemical reactions. And astrophysicists will become experimentalists, using beams 10 billion times brighter than synchrotron radiation to create the extreme state of matter believed to exist within forming stars. With U.S. and European machines in the works, Japan wants into the club reports Dennis Normile in Science.
Nature: Werner Marx and Andreas Barth have decided to revise their recently published paper on the future of high-temperature superconductivity research after complaints about their ominous conclusions. They stand by their data, they say, but add that some things could perhaps have
been better phrased.
Continue reading Superconductivity researchers complain about paper.
