Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Cesium atoms shaken, not stirred, to create elusive excitation in superfluid

06.02.2015

Scientists discovered in 1937 that liquid helium-4, when chilled to extremely low temperatures, became a superfluid that could leak through glass, overflow its containers, or eternally gush like a fountain.

Future Nobel laureate Lev Landau came along in 1941, predicting that superfluid helium-4 should contain an exotic, particle-like excitation called a roton. But scientists, including Landau, Nobel laureate Richard Feynman and Wolf Prize recipient Philippe Nozières have debated what structure the roton would take ever since.


University of Chicago scientists can create an exotic, particle-like excitation called a roton in superfluids with the tabletop apparatus pictured here. Posing from left are graduate students Li-Chung Ha and Logan Clark, and physics Professor Cheng Chin.

Credit: Rob Kozloff, University of Chicago

"Even nowadays, after seven decades, it remains an issue of interest and controversy," said Cheng Chin, professor in physics at the University of Chicago. But in a new paper published Feb. 3, 2015, in Physical Review Letters, Chin and four associates describe how they can create roton structure in a new system: atomic superfluid of cesium-133 in the laboratory.

Scientists who specialize in superfluids have found it difficult to study rotons. Chin's team has pioneered a system that will make it much easier to reveal the long-cloaked mysteries of the roton.

The UChicago researchers generated artificial rotons using what they call the shaken lattice technique. With this technique, the physicists created a superfluid in a one-foot cylindrical chamber cooled to a temperature of approximately 15 nano-Kelvin, just a tiny fraction of a degree above absolute zero (minus 459.6 degrees Fahrenheit).

During the experiment, 30,000 cesium atoms became trapped in a crossing pattern of infrared laser beams. This optical lattice holds the atoms fast, like eggs in a crate, while gently shaking them.

Superfluidity in 10 seconds

"We need about 10 seconds to reach that temperature to prepare a superfluid as our first step," Chin said. "It is a brand new idea that shaking the optical lattice leads to the emergence of the rotons."

The superfluid persists for several seconds, during which time the physicists create the roton structure and image it to see how the structure influences the superfluid's properties.

Competing research teams at the University of Science and Technology in Shanghai, China, and at Washington State University also succeeded in creating roton structure using a different technique within few weeks after the Chicago group announced the result last summer. Those teams used additional laser beams to excite the atoms in the proper way.

"We approached the challenge to create rotons based on a new technology that we recently developed," said Li-Chung Ha, a graduate student in physics at UChicago. The lead author of the Physical Review Letters paper, Ha played a key role in developing the shaken lattice and in-situ imaging techniques used to collect the roton data.

Chin's research group developed the lattice shaking technique over a period of years. In 2013, Ha, Chin and UChicago postdoctoral scholar Colin V. Parker published a paper in Nature Physics showing that a variation of that technique could reveal interesting magnetic features in ultracold atoms. Later, they realized that they could use the same technique to create roton structure.

Engineering roton excitation

"With this technique, we can engineer an excitation spectrum of the atoms," Ha said. This feature, a hallmark of superfluid helium, is one of three pieces of evidence reported in the paper indicating that Ha and his associates had successfully created roton structure.

The other two lines of evidence include the measurements of roton energy confirming that its manifestation depends on the atomic interaction. The UChicago team also observed how roton excitations affect the superfluidity by dragging a laser speckle pattern across the superfluid.

"Experimentally, we see that a superfluid will become weaker in the presence of roton structure," Chin said. A superfluid can flow with no friction up to a maximum speed, called "superfluid critical velocity." Rotons suppress the critical velocity, which is the opposite of the desired goal to improve the robustness of superfluidity.

How robust can superfluidity be?

Researchers have proposed many ways to increase the robustness of superconductors, and atomic superfluids offer experimental means to test these ideas, Chin said.

"Superconductors can transfer energy without dissipation, that is, without energy loss, so a robust superconducting material can find widespread applications everywhere," he said. At the moment, power companies still use copper wire for energy transmission, which carries with it energy losses ranging from 30 to 40 percent from power plant to home or office.

Switching to superconductivity is currently impractical because superconducting material is expensive, and it works only at extremely low temperatures. More importantly, Chin noted, "a single superconducting wire can only carry a limited amount of energy."

"Our experiments provide a new platform to study excitations of a superfluid. They can help us better identify the key issues that limit the robustness of superconductivity," he said.

Media Contact

Steve Koppes
skoppes@uchicago.edu
773-702-8366

 @UChicago

http://www-news.uchicago.edu 

Steve Koppes | EurekAlert!

More articles from Physics and Astronomy:

nachricht Nanomagnetism in X-ray Light
23.03.2017 | Max-Planck-Institut für Intelligente Systeme

nachricht When helium behaves like a black hole
22.03.2017 | University of Vermont

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: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Vanishing capillaries

23.03.2017 | Health and Medicine

Nanomagnetism in X-ray Light

23.03.2017 | Physics and Astronomy

Pulverizing electronic waste is green, clean -- and cold

22.03.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>