(Press-News.org) Physicists at the University of California, Berkeley, have cooled a gas to the quietest state ever achieved, hoping to detect faint quantum effects lost in the din of colder but noisier fluids.
While the ultracold gas's temperature - a billionth of a degree above absolute zero - is twice as hot as the record cold, the gas has the lowest entropy ever measured. Entropy is a measure of disorder or noise in a system; a record low temperature gas isn't necessarily the least noisy.
"This 'lowest entropy' or 'lowest noise' condition means that the quantum gas can be used to bring forth subtle quantum mechanical effects which are a main target for modern research on materials and on many-body physics," said co-author Dan Stamper-Kurn, a UC Berkeley professor of physics. "When all is quiet and all is still, one might discern the subtle music of many-body quantum mechanics."
The quantum gas, a so-called Bose-Einstein condensate, consisted of about a million rubidium atoms trapped by a beam of light, isolated in a vacuum and cooled to their lowest energy state. The entropy and temperature were so low that the researchers had to develop a new type of thermometer to measure them.
While achieving extremely low temperatures may make the record books, UC Berkeley graduate student Ryan Olf said, what scientists aim for today are low-entropy states they can study to understand more interesting but difficult-to-study materials.
The UC Berkeley team's ability to manipulate ultracold, low-entropy gases will allow them to study these quantum systems, including quantum magnets - potentially useful in quantum computers - and high-temperature superconductors. High-temperature superconductors are experimental materials that display superconductivity - electrical flow without resistance - at relatively high temperatures compared to the 3 or 4 degrees Celsius above absolute zero typical of today's conventional superconductors.
"One of the holy grails of modern physics is to understand these exotic materials well enough to design one that is superconducting without requiring any cooling at all," Olf said. "By studying the properties of low-entropy gases in various configurations, our community of researchers hope to learn what makes these fascinating materials work the way they do."
Olf said that the entropy per particle, rather than the temperature, is the pertinent parameter when comparing systems, and the ultracold gases that had been produced until now struggled to reach the low entropies that would be required to test models of these materials.
"In a very real sense, this constitutes the coldest gas ever produced, at 50 times lower than the temperature at which quantum statistical effects become manifest, the Bose-Einstein condensation temperature," he said.
The details of the experiment were published online last month and will appear in a future print edition of the journal Nature Physics.
Reducing the rumble
Stamper-Kurn and his laboratory team chill gases to temperatures so low that quantum effects take over, which leads to strange "superfluid" behavior, such as frictionless flow. Superfluid helium is famous for climbing up and over the lip of a cup. Superfluid gases exhibit vortices - tiny tornadoes like those created when you stir a cup of coffee - that live forever.
At these low temperatures, Stamper-Kurn said, the low-energy excitations or jiggling of the atoms are sound waves. "Temperature generates something like a constant rumble of sound in the gas, and the entropy is like a count of how many sound-wave excitations remain. The colder a gas becomes, the less entropy it has and the quieter it is."
Normally, a Bose-Einstein condensate is a mixture of a quantum gas and a normal gas. Its temperature is determined by measuring the thermal properties of the normal gas. A low-entropy gas is almost all quantum gas, however, so the team had to find a different way to measure the temperature. They did so by tilting the magnetization of the atomic spins and measuring thermal properties of the tilted magnetization, essentially creating a magnon thermometer.
The tilted spins also helped them cool the gas to its low-entropy state by enhancing the evaporative cooling that researchers have long relied on to produce ultracold gases. In addition to removing hot atoms to reduce the average temperature of the gas, they used evaporative cooling of the thermalized spins to reduce the temperature to 1 nanoKelvin (one-billionth of a degree above absolute zero), corresponding to an entropy 100 times lower than previous experiments, Olf said.
INFORMATION:
Other co-authors are Fang Fang, G. Edward Marti and Andrew MacRae. The work is supported by the National Aeronautics and Space Administration, the U.S. Air Force Office of Scientific Research and the National Science Foundation.
Glenview, Ill. (August 4, 2015)--Researchers have found the risk for hospital readmission to be nearly three times higher after COPD exacerbation if a follow-up visit to a pulmonologist is skipped. The Israeli study published today in the journal CHEST The Association Between Hospital Readmission and Pulmonologist Follow-up Visits in Patients With COPD examined the impact of a pulmonologist follow-up visit during the month after discharge from the hospital on reducing readmissions.
COPD exacerbations account for 500,000 hospital admissions and $18 billion in direct health-care ...
Glenview, Ill. (August 4, 2015) -- A case study published in the August issue of the journal CHEST found lenalidomide treatments may have an immediate effect in the treatment of sarcoidosis-related symptoms. Sarcoidosis, a disease that involves abnormal collections of inflammatory cells that can form nodules in various organs, can affect individuals from all racial and age groups. To date, no optimal therapies have been effective in managing this condition.
This finding was reported in the case of a 71-year-old woman with a long-standing history of refractory pulmonary ...
An expanded program of treatment for hypertension could prevent about 800,000 cardiovascular disease (CVD) events every year in China, according to a modeling study published this week in PLOS Medicine. The predictions of this simulation, reported by Andrew Moran of Columbia University and colleagues, indicate that such a program should also be borderline cost-effective, provided low cost essential anti-hypertensive drugs are used.
Hypertension is the leading cardiovascular risk factor in China, the world's most populous country. About 325 million adults in China have ...
UNIVERSITY OF CALIFORNIA, BERKELEY'S HAAS SCHOOL OF BUSINESS- Marketers would love to get inside the consumer brain. And now they can. Researchers at UC Berkeley's Haas School of Business are using functional magnetic resonance imaging (fMRI) to see if what people say about brands matches what they are actually thinking.
In their paper, "From 'Where' to 'What': Distributed Representations of Brand Associations in the Human Brain (Journal of Marketing Research: August 2015, Vol. 52, No. 4), co-authors Ming Hsu and Leif Nelson, Berkeley-Haas marketing professors, and Yu-Ping ...
While most people might know some algae as "pond scum," to the U.S. Department of Energy (DOE), they are tiny organisms that could provide a source of sustainable fuels. Like plants, they can convert light into energy-rich chemical compounds; unlike plants, they require less space and don't need arable soil to grow.
Some algae like Chlamydomonas reinhardtii (or "Chlamy," as it's known to its large research community) produce energy-dense oils or lipids when stressed, and these lipids can then be converted into fuels. However, researchers walk a fine line in not killing ...
Most robots on a factory floor are fairly ham-handed: Equipped with large pincers or claws, they are designed to perform simple maneuvers, such as grabbing an object, and placing it somewhere else in an assembly line. More complex movements, such as adjusting the grasp on an object, are still out of reach for many industrial robots.
Engineers at MIT have now hit upon a way to impart more dexterity to simple robotic grippers: using the environment as a helping hand. The team, led by Alberto Rodriguez, an assistant professor of mechanical engineering, and graduate student ...
Washington, DC-Even before a child is conceived, the parents' exposure to environmental stressors can alter the way genes are expressed and ultimately harm the child's health when those genes are passed down to the next generation, according to a new article published in the Endocrine Society's journal Endocrinology.
Exposure to environmental stressors such as endocrine-disrupting chemicals, psychological stress and malnutrition may result in disadvantageous epigenetic "reprogramming" that can echo through multiple generations. When these stressors disrupt early developmental ...
WASHINGTON D.C., August 4, 2015 -- The following articles are freely available online from Physics Today, the world's most influential and closely followed magazine devoted to physics and the physical science community.
You are invited to read, share, blog about, link to, or otherwise enjoy:
1) IS PHYSICS RESEARCH ANOTHER CASUALTY OF UKRAINIAN CONFLICT?
David Kramer of Physics Today discusses the negative impact that the conflict in eastern Ukraine has had on physicists and students forced to relocate from their homes and universities.
"More than 25 universities and ...
More than 2 percent of all emergency department visits are now related to nontraumatic dental conditions, according to a study by researchers at Stanford University, the University of California-San Francisco, Truven Health Analytics and the federal Agency for Healthcare Research and Quality.
Although the expansion of Medicaid under the Affordable Care Act has made millions of low-income and rural Americans eligible for health insurance, many states don't provide dental coverage for adults under their Medicaid programs. Paying for dental insurance on the individual market ...
This news release is available in French. In summertime, bats are a common feature in the night sky, swooping around backyards to gobble up mosquitos. Bats also help with crops: they act as a natural pesticide by feeding on harmful insects.
But these winged mammals are now under threat. As agricultural intensification expands across the world, the conversion of their natural habitats has caused a dramatic decline in population. North American bats are also plagued with white-nose syndrome, an emerging infectious disease that's decimating their numbers.
"Many bat ...
