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 A 100-year-old physics problem has been solved at EPFL
23.06.2017 | Ecole Polytechnique Fédérale de Lausanne

nachricht Quantum thermometer or optical refrigerator?
23.06.2017 | National Institute of Standards and Technology (NIST)

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: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Quantum thermometer or optical refrigerator?

23.06.2017 | Physics and Astronomy

A 100-year-old physics problem has been solved at EPFL

23.06.2017 | Physics and Astronomy

Equipping form with function

23.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>