Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Ultracold atoms produce long-sought quantum mix

16.03.2006


Unbalanced superfluid could be akin to exotic matter found in Quark Star

Rice University physicist Randall Hulet will discuss breakthrough efforts to create a long-sought quantum superfluid at a press conference at 2:30 p.m. today at the American Physical Society’s 2006 March Meeting.

In January, Hulet’s laboratory reported in the journal Science the observation of an elusive quantum state – a superfluid of fermions with mismatched numbers of dance partners. Despite more than 40 years of theoretical musings about what would occur in such a case, the result -- a cluster of matched pairs surrounded by a cloud of would-be dance partners -- was largely unexpected, and it has opened the door to several intriguing new avenues of investigation.



Hulet will discuss published findings and ongoing investigations today in room 334 of the Baltimore Convention Center.

Rice’s experiments offer physicists a new window into two of the most intriguing and least understood phenomena in physics – superconductivity and superfluidity.

In the bizarre and rule-bound world of quantum physics, every tiny speck of matter has something called "spin" -- an intrinsic trait like eye color -- that cannot be changed and which dictates, very specifically, what other bits of matter the speck can share quantum space with. Because of their spins, fermions are the most antisocial of quantum particles. But when they do get together, fermion pairings enable such wondrous things as superconductivity and superfluidity.

Both phenomena result from a change in the phase of matter. Anyone who has seen ice melt has seen matter change phases, and when electrons, atoms and other specks of matter change quantum phases, they behave just as differently as do ice and water in a glass.

Superconducting and superfluid phases of matter occur in fermions only when quantum effects become dominant. Because thermodynamic forces are typically so powerful that they overwhelm quantum interactions -- like loud music overwhelms the whisper of someone nearby -- superconductivity and superfluidity usually only occur in extreme cold.

In the Rice experiments, when temperatures drop to within a few billionths of a degree of absolute zero, fermions with equal but opposite spin become attracted to one another and behave, in some respects, like one particle. Like a couple on the dance floor, they don’t technically share space, but they move in unison. In superconductors, these dancing pairs allow electrical current to flow through the material without any resistance at all, a property that engineers have long dreamed of harnessing to eliminate "leakage" in power cables, something that costs billions of dollars per year in the U.S. alone.

The superconducting and superfluid phases are analogous except that superconductivity happens with particles carrying an electrical charge and superfluidity occurs in electrically neutral particles. In superfluids, fermionic pairing leads to a complete absence of viscosity – like a wave rippling back and forth in a swimming pool without ever diminishing.

"Conventional theory tells us superconductivity or superfluidity occurs only in the presence of an equal number of spin-up and spin-down particles," said Hulet, the Fayez Sarofim Professor of Physics and Astronomy. "Physicists have speculated for almost 50 years about what would happen if this condition were not met.

"Because of the pristine and controlled nature of ultracold atoms, we’re able to offer definitive evidence of what happens with mismatched numbers of spin-up and spin-down particles."

Ultracold experiments at temperatures just a few billionths of a degree above absolute zero are Hulet’s specialty. It’s only been technically possible to chill atoms to these temperatures for the past 10 years, but in that time, this ability has proved remarkably useful for testing the predictions of quantum mechanics and for exploring the properties of what physicists call "many-body phenomena," including superconductivity and superfluidity.

Hulet’s team cooled a mixture of fermionic lithium-6 atoms to about 30-billionths of a degree above absolute zero. That’s far colder than any temperature in nature -- even in deepest interstellar space -- and it’s sufficient to quell virtually all thermodynamic interaction in the atoms, leaving them subject to superfluid quantum pairing.

Using radio waves, Hulet’s team can alter the ratio of spin-up and spin-down atoms in the cooled sample with great precision. They have found that the superfluid is able to tolerate an excess of up to 10 percent unpaired fermions with no detrimental effects.

"The gas behaves as if it is still perfectly paired, which is quite remarkable given the excess of spin-up atoms," Hulet said. "This was unexpected, and it could signal a new, exotic form of pairing that may also occur in unconventional superconductors or in the quark soup that’s predicted to exist at the heart of the densest neutron stars."

In the largest neutron stars -- known as "quark stars" -- a mass about five times greater than the sun is pressed into a space smaller than the island of Manhattan. Some physics theorists believe gravity is so strong at the heart of these stars that it creates something called "strange matter," a dense superfluid of up quarks, down quarks and strange quarks.

Hulet’s team has also found that increasing the ratio of spin-up to spin-down atoms eventually causes a phase change. When unpaired spin-up atoms rise above 10 percent of the total sample, the unpaired loners are suddenly expelled, leaving a core of superfluid pairs surrounded by a shell of excess spin-up atoms.

Ben Stein | EurekAlert!
Further information:
http://www.rice.edu
http://www.aip.org

More articles from Physics and Astronomy:

nachricht CCNY physicists master unexplored electron property
26.07.2017 | City College of New York

nachricht Large, distant comets more common than previously thought
26.07.2017 | University of Maryland

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Carbon Nanotubes Turn Electrical Current into Light-emitting Quasi-particles

Strong light-matter coupling in these semiconducting tubes may hold the key to electrically pumped lasers

Light-matter quasi-particles can be generated electrically in semiconducting carbon nanotubes. Material scientists and physicists from Heidelberg University...

Im Focus: Flexible proximity sensor creates smart surfaces

Fraunhofer IPA has developed a proximity sensor made from silicone and carbon nanotubes (CNT) which detects objects and determines their position. The materials and printing process used mean that the sensor is extremely flexible, economical and can be used for large surfaces. Industry and research partners can use and further develop this innovation straight away.

At first glance, the proximity sensor appears to be nothing special: a thin, elastic layer of silicone onto which black square surfaces are printed, but these...

Im Focus: 3-D scanning with water

3-D shape acquisition using water displacement as the shape sensor for the reconstruction of complex objects

A global team of computer scientists and engineers have developed an innovative technique that more completely reconstructs challenging 3D objects. An ancient...

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

 
Latest News

CCNY physicists master unexplored electron property

26.07.2017 | Physics and Astronomy

Molecular microscopy illuminates molecular motor motion

26.07.2017 | Life Sciences

Large-Mouthed Fish Was Top Predator After Mass Extinction

26.07.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>