PRESS-NEWS.org - Press Release Distribution
PRESS RELEASES DISTRIBUTION

Disorderly conduct

Probing the role of disorder in quantum coherence

2012-07-20
(Press-News.org) A new experiment conducted at the Joint Quantum Institute (JQI)* examines the relationship between quantum coherence, an important aspect of certain materials kept at low temperature, and the imperfections in those materials. These findings should be useful in forging a better understanding of disorder, and in turn in developing better quantum-based devices, such as superconducting magnets.

Most things in nature are imperfect at some level. Fortunately, imperfections---a departure, say, from an orderly array of atoms in a crystalline solid---are often advantageous. For example, copper wire, which carries so much of the world's electricity, conducts much better if at least some impurity atoms are present.

In other words, a pinch of disorder is good. But there can be too much of this good thing. The issue of disorder is so important in condensed matter physics, and so difficult to understand directly, that some scientists have been trying for some years to simulate with thin vapors of cold atoms the behavior of electrons flowing through solids trillions of times more dense. With their ability to control the local forces over these atoms, physicists hope to shed light on more complicated case of solids.

That's where the JQI experiment comes in. Specifically, Steve Rolston and his colleagues have set up an optical lattice of rubidium atoms held at temperature close to absolute zero. In such a lattice atoms in space are held in orderly proximity not by natural inter-atomic forces but by the forces exerted by an array of laser beams. These atoms, moreover, constitute a Bose Einstein condensate (BEC), a special condition in which they all belong to a single quantum state.

This is appropriate since the atoms are meant to be a proxy for the electrons flowing through a solid superconductor. In some so called high temperature superconductors (HTSC), the electrons move in planes of copper and oxygen atoms. These HTSC materials work, however, only if a fillip of impurity atoms, such as barium or yttrium, is present. Theorists have not adequately explained why this bit of disorder in the underlying material should be necessary for attaining superconductivity.

The JQI experiment has tried to supply palpable data that can illuminate the issue of disorder. In solids, atoms are a fraction of a nanometer (billionth of a meter) apart. At JQI the atoms are about a micron (a millionth of a meter) apart. Actually, the JQI atom swarm consists of a 2-dimensional disk. "Disorder" in this disk consists not of impurity atoms but of "speckle." When a laser beam strikes a rough surface, such as a cinderblock wall, it is scattered in a haphazard pattern. This visible speckle effect is what is used to slightly disorganize the otherwise perfect arrangement of Rb atoms in the JQI sample.

In superconductors, the slight disorder in the form of impurities ensures a very orderly "coherence" of the supercurrent. That is, the electrons moving through the solid flow as a single coordinated train of waves and retain their cohesiveness even in the midst of impurity atoms.

In the rubidium vapor, analogously, the slight disorder supplied by the speckle laser ensures that the Rb atoms retain their coordinated participation in the unified (BEC) quantum wave structure. But only up to a point. If too much disorder is added---if the speckle is too large---then the quantum coherence can go away. Probing this transition numerically was the object of the JQI experiment. The setup is illustrated in figure 1.

And how do you know when you've gone too far with the disorder? How do you know that quantum coherence has been lost? By making coherence visible.

The JQI scientists cleverly pry their disk-shaped gas of atoms into two parallel sheets, looking like two thin crepes, one on top of each other. Thereafter, if all the laser beams are turned off, the two planes will collide like miniature galaxies. If the atoms were in a coherent condition, their collision will result in a crisp interference pattern showing up on a video screen as a series of high-contrast dark and light stripes.

If, however, the imposed disorder had been too high, resulting in a loss of coherence among the atoms, then the interference pattern will be washed out. Figure 2 shows this effect at work. Frames b and c respectively show what happens when the degree of disorder is just right and when it is too much.

"Disorder figures in about half of all condensed matter physics," says Steve Rolston. "What we're doing is mimicking the movement of electrons in 3-dimensional solids using cold atoms in a 2-dimensional gas. Since there don't seem to be any theoretical predictions to help us understand what we're seeing we've moved into new experimental territory."

Where does the JQI work go next? Well, in figure 2a you can see that the interference pattern is still visible but somewhat garbled. That arises from the fact that for this amount of disorder several vortices---miniature whirlpools of atoms---have sprouted within the gas. Exactly such vortices among electrons emerge in superconductivity, limiting their ability to maintain a coherent state.

The new results are published in the New Journal of Physics: http://iopscience.iop.org/1367-2630/14/7/073024?fromSearchPage=true "Disorder-driven loss of phase coherence in a quasi-2D cold atom system," by M C Beeler, M E W Reed, T Hong, and S L Rolston.

Another of the JQI scientists, Matthew Beeler, underscores the importance of understanding the transition from the coherent state to incoherent state owing to the fluctuations introduced by disorder:

"This paper is the first direct observation of disorder causing these phase fluctuations. To the extent that our system of cold atoms is like a HTSC superconductor, this is a direct connection between disorder and a mechanism which drives the system from superconductor to insulator."



INFORMATION:



(*)The Joint Quantum Institute is operated jointly by the National Institute of Standards and Technology in Gaithersburg, MD and the University of Maryland in College Park.



ELSE PRESS RELEASES FROM THIS DATE:

Novel anti-malarial drug target identified

2012-07-20
An international team of scientists, led by researchers from the Department of Pediatrics at the University of California, San Diego School of Medicine, have identified the first reported inhibitors of a key enzyme involved in survival of the parasite responsible for malaria. Their findings, which may provide the basis for anti-malarial drug development, are currently published in the online version of the Journal of Medicinal Chemistry. Tropical malaria is responsible for more than 1.2 million deaths annually. Severe forms of the disease are mainly caused by the parasite ...

Blood vessel forming potential of stem cells from human placenta and umbilical cord blood

2012-07-20
Tampa, Fla. (July 19, 2012) – A study comparing whether endothelial colony-forming cells (ECFCs) derived from human placenta or those derived from human umbilical cord blood are more proliferative and better for forming new blood vessels has found that ECFCs derived from human placenta are more vasculogenic. The study, carried out by researchers at the Indiana School of Medicine, is published in a recent issue of Cell Medicine [2(3)] and is freely available on-line at: http://www.ingentaconnect.com/content/cog/cm. "Circulating ECFCs isolated from umbilical cord blood ...

Being in awe can expand time and enhance well-being

2012-07-20
It doesn't matter what we've experienced – whether it's the breathtaking scope of the Grand Canyon, the ethereal beauty of the Aurora Borealis, or the exhilarating view from the top of the Eiffel Tower – at some point in our lives we've all had the feeling of being in a complete and overwhelming sense of awe. Awe seems to be a universal emotion, but it has been largely neglected by scientists—until now. Psychological scientists Melanie Rudd and Jennifer Aaker of Stanford University Graduate School of Business and Kathleen Vohs of the University of Minnesota Carlson ...

Colorful science sheds light on solar heating

2012-07-20
A crucial, and often underappreciated, facet of science lies in deciding how to turn the raw numbers of data into useful, understandable information – often through graphs and images. Such visualization techniques are needed for everything from making a map of planetary orbits based on nightly measurements of where they are in the sky to colorizing normally invisible light such as X-rays to produce "images" of the sun. More information, of course, requires more complex visualizations and occasionally such images are not just informative, but beautiful too. Such is the ...

IRVE-3 flight hardware test sounding rocket

2012-07-20
NASA will launch an inflatable aeroshell/heat shield technology demonstrator on a Black Brant XI sounding rocket July 22 from the agency's launch range at the Wallops Flight Facility in Virginia. The Inflatable Reentry Vehicle Experiment (IRVE-3) is the third in a series of suborbital flight tests of this new technology. Technicians will vacuum pack the uninflated 10-foot (3.05 meters) diameter cone of high-tech inner tubes into a 22-inch (56 centimeters) diameter sounding rocket. During the flight test an on board system will inflate the tubes -- stretching a thermal ...

Tropical Depression Khanun blankets South Korea

2012-07-20
Tropical Depression Khanun came ashore with some heavy rainfall in the morning hours (local time) on Thursday, July 19. NASA's Terra satellite captured an image of Khanun's clouds on July 19, covering all of South Korea like a blanket. The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument onboard NASA's Terra satellite captured a true-color image of Tropical Depression Khanun over South Korea on July 19, 2012 at 0225 UTC, or 11:25 a.m. local time, Seoul (10:25 p.m. EDT/U.S. on July 18). The last advisory on Khanun from the Joint Typhoon Warning Center ...

Vitamin D may protect against lung function impairment and decline in smokers

2012-07-20
Vitamin D deficiency is associated with worse lung function and more rapid decline in lung function over time in smokers, suggesting that vitamin D may have a protective effect against the effects of smoking on lung function, according to a new study from researchers in Boston. "We examined the relationship between vitamin D deficiency, smoking, lung function, and the rate of lung function decline over a 20 year period in a cohort of 626 adult white men from the Normative Aging Study," said lead author Nancy E. Lange, MD, MPH, of the Channing Laboratory, Brigham and ...

CPAP treatment effective in patients with milder OSA and daytime sleepiness

2012-07-20
Continuous positive airway pressure (CPAP), well established as an effective treatment for severe obstructive sleep apnea (OSA), is also effective in patients with mild and moderately severe OSA and daytime sleepiness, according to a new study. "The evidence for the efficacy of CPAP in patients with milder OSA is limited and conflicting," said lead author Terri E. Weaver, PhD, RN, professor and dean of the University of Illinois at Chicago College of Nursing. "Our multi-site, double-blind, randomized trial, the first placebo-controlled study to use sham CPAP in sleepy ...

Rutgers study: Anxiety disorders in poor moms likely to result from poverty, not mental illness

2012-07-20
NEW BRUNSWICK, N.J. – Poor mothers are more likely to be classified as having the mental illness known as generalized anxiety disorder (GAD) because they live in poverty – not because they are suffering from a psychiatric disorder, according to Rutgers researchers. Judith C. Baer, an associate professor in the School of Social Work, and her team, in the study, "Is it Generalized Anxiety Disorder or Poverty? An Examination of Poor Mothers and Their Children," published online in Child and Adolescent Social Work, argue that although high levels of stress over long periods ...

Racially diverse suburbs growing faster than white suburbs but resegregation threatens prosperity

2012-07-20
Racially diverse suburbs are growing faster than white suburbs, but resegregation threatens their prosperity and stability, according to a study entitled, "America's Racially Diverse Suburbs: Opportunities and Challenges," released this week by the Institute on Metropolitan Opportunity at the University of Minnesota Law School. Long perceived as predominantly prosperous white enclaves, suburbs are now at the cutting edge of racial, ethnic and political change in America. The study finds the number of racially diverse suburbs, municipalities ranging from 20-60 percent ...

LAST 30 PRESS RELEASES:

Signs identified that precede sudden arrhythmic death syndrome in young people

Discovery of bacteria's defence against viruses becomes a piece of the puzzle against resistance

Pre-eclampsia is associated with earlier onset and higher incidence of cardiovascular risk factors

Warwick astronomers discover doomed pair of spiralling stars on our cosmic doorstep

Soil conditions significantly increase rainfall in world’s megastorm hotspots

NK cells complexed with bispecific antibody yield high response rates in patients with lymphoma

Planetary health diet and mediterranean diet associated with similar survival and sustainability benefits

Singapore launches national standard to validate antimicrobial disinfectant products

Molecular stool test could improve detection of tuberculosis in adults with HIV

Suspected fibrocartilaginous embolus in Asian small-clawed otter (Aonyx cinereus)

Enhancing heat transfer using the turbulent flow of viscoelastic fluids

Exercise as an anti-ageing intervention to avoid detrimental impact of mental fatigue

UMass Amherst Nursing Professor Emerita honored as ‘Living Legend’

New guidelines aim to improve cystic fibrosis screening

Picky eaters by day, buffet by night: Butterfly, moth diets sync to plant aromas

Pennington Biomedical’s Dr. Leanne Redman honored with the E. V. McCollum Award from the American Society for Nutrition

CCNY physicists uncover electronic interactions mediated via spin waves

Researchers’ 3D-printing formula may transform future of foam

Nurture more important than nature for robotic hand

Drug-delivering aptamers target leukemia stem cells for one-two knockout punch

New study finds that over 95% of sponsored influencer posts on Twitter were not disclosed

New sea grant report helps great lakes fish farmers navigate aquaculture regulations

Strain “trick” improves perovskite solar cells’ efficiency

How GPS helps older drivers stay on the roads

Estrogen and progesterone stimulate the body to make opioids

Dancing with the cells – how acoustically levitating a diamond led to a breakthrough in biotech automation

Machine learning helps construct an evolutionary timeline of bacteria

Cellular regulator of mRNA vaccine revealed... offering new therapeutic options

Animal behavioral diversity at risk in the face of declining biodiversity

Finding their way: GPS ignites independence in older adult drivers

[Press-News.org] Disorderly conduct
Probing the role of disorder in quantum coherence