Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

A new path to understanding second sound in Bose-Einstein condensates

02.07.2019

When you jump into a lake and hold your head under water, everything sounds different. Apart from the different physiological response of our ears in air and water, this derives from the different sound propagation in water compared to air. Sound travels faster in water, checking in at 1493 m/s, on a comfortable summer day of 25°C. Other liquids have their own sound velocity, like alcohol with 1144 m/s, and helium, if you go to a chilling -269°C for its liquefied state, with 180 m/s.

These liquids are referred to as classical liquids, examples for one of the primary states of matter. But if we cool down that helium a few degrees more, something dramatic happens, it turns into a quantum liquid. This macroscopic display of quantum mechanics is a superfluid, a liquid that flows without friction.


There are two sound velocities in a Bose-Einstein condensate. In addition to the normal sound propagation there is second sound, which is a quantum phenomenon. Scientists around Ludwig Mathey from the University of Hamburg have put forth a new theory for this phenomenon.

Credit: UHH, Mathey group

So what do you hear if you make the unfortunate decision to stick your head into this liquid? Surprisingly, you will hear the same sound twice. In addition to the normal sound of a liquid there is the phenomenon of second sound that derives from the quantum nature of this liquid.

If someone says something to you while immersed in superfluid helium, you will hear it as first sound first, and then get a second chance to listen when it arrives as second sound, albeit strongly muted. For superfluid helium, second sound is quite a bit slower than first sound, with 25 m/s vs. 250 m/s, between 1 and 2 Kelvin.

While the conventional theory of second sound has been successful for superfluid helium, the rise of Bose-Einstein condensates of ultracold atoms has posed new challenges.

A team of scientists led by Ludwig Mathey from the University of Hamburg have put forth a new theory that captures second sound in these quantum liquids, recently published in Physical Review A.

'For superfluid helium, second sound is slower than first sound', explains co-author Vijay Singh, 'but we were amazed to find that this is not necessarily true, that the second pulse can be faster'. A new theoretical approach was needed to capture this. Modern problems require modern solutions, as they say.

'We generalized the Feynman path integral to expand the theory of superfluids describes lead author Ilias Seifie the conceptual advance. While the path integral, brilliantly conceived by Richard Feynman, formulates quantum mechanics as a sum over trajectories, these trajectories themselves are classical.

'We modified what these trajectories look like' continues Seifie, 'in our path integral they contain information about quantum fluctuations.' Imagine a pool noodle that stretches from A to B as a poor man's visualization of a trajectory that enters the Feynman path integral.

The cross-section of the noodle is more or less round with a constant diameter along its length. But in the new path integral, the shape of the cross section can vary, it can take elliptical shapes, imagine squeezing the pool noodle together. Fittingly, physicists refer to these quantum mechanical states as squeezed states.

'This approach is widely applicable', explains Ludwig Mathey, 'it can be applied to any method that is based on path integrals.' Indeed, many phenomena at the interface of quantum and classical physics can be imagined to be better understood with this approach. One might just squeeze a bit more insight out of nature with this new framework.

###

Citation:

Vijay Singh, Ilias Seifie, Ludwig Mathey "Squeezed-field path-integral description of second sound in Bose-Einstein condensates" Phys. Rev. A 100, 013602 - Published 1 July 2019 DOI: 10.1103/PhysRevA.100.013602

Media Contact

Prof. Dr. Ludwig Mathey
lmathey@physnet.uni-hamburg.de
49-408-998-6505

 @unihh

http://www.uni-hamburg.de/index_e.html 

Prof. Dr. Ludwig Mathey | EurekAlert!
Further information:
http://dx.doi.org/10.1103/PhysRevA.100.013602

More articles from Physics and Astronomy:

nachricht Redefining the Limits of Measurement Accuracy
02.07.2019 | Leibniz Universität Hannover

nachricht Tracking down dark matter
02.07.2019 | Johannes Gutenberg-Universität Mainz

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: The secret of mushroom colors

Mushrooms: Darker fruiting bodies in cold climates

The fly agaric with its red hat is perhaps the most evocative of the diverse and variously colored mushroom species. Hitherto, the purpose of these colors was...

Im Focus: First results of the new Alphatrap experiment

Physicists at the Max Planck Institute for Nuclear Physics in Heidelberg report the first result of the new Alphatrap experiment. They measured the bound-electron g-factor of highly charged (boron-like) argon ions with unprecedented precision of 9 digits. In comparison with a new highly accurate quantum electrodynamic calculation they found an excellent agreement on a level of 7 digits. This paves the way for sensitive tests of QED in strong fields like precision measurements of the fine structure constant α as well as the detection of possible signatures of new physics. [Physical Review Letters, 27 June 2019]

Quantum electrodynamics (QED) describes the interaction of charged particles with electromagnetic fields and is the most precisely tested physical theory. It...

Im Focus: Experimental physicists redefine ultrafast, coherent magnetism

For the first time ever, experimental physicists have been able to influence the magnetic moment of materials in sync with their electronic properties. The coupled optical and magnetic excitation within one femtosecond corresponds to an acceleration by a factor of 200 and is the fastest magnetic phenomenon that has ever been observed.

Electronic properties of materials can be directly influenced via light absorption in under a femtosecond (10-15 seconds), which is regarded as the limit of...

Im Focus: Fraunhofer IDMT demonstrates its method for acoustic quality inspection at »Sensor+Test 2019« in Nürnberg

From June 25th to 27th 2019, the Fraunhofer Institute for Digital Media Technology IDMT in Ilmenau (Germany) will be presenting a new solution for acoustic quality inspection allowing contact-free, non-destructive testing of manufactured parts and components. The method which has reached Technology Readiness Level 6 already, is currently being successfully tested in practical use together with a number of industrial partners.

Reducing machine downtime, manufacturing defects, and excessive scrap

Im Focus: Successfully Tested in Praxis: Bidirectional Sensor Technology Optimizes Laser Material Deposition

The quality of additively manufactured components depends not only on the manufacturing process, but also on the inline process control. The process control ensures a reliable coating process because it detects deviations from the target geometry immediately. At LASER World of PHOTONICS 2019, the Fraunhofer Institute for Laser Technology ILT will be demonstrating how well bi-directional sensor technology can already be used for Laser Material Deposition (LMD) in combination with commercial optics at booth A2.431.

Fraunhofer ILT has been developing optical sensor technology specifically for production measurement technology for around 10 years. In particular, its »bd-1«...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on UV LED Technologies & Applications – ICULTA 2020 | Call for Abstracts

24.06.2019 | Event News

SEMANTiCS 2019 brings together industry leaders and data scientists in Karlsruhe

29.04.2019 | Event News

Revered mathematicians and computer scientists converge with 200 young researchers in Heidelberg!

17.04.2019 | Event News

 
Latest News

Generation and sampling of quantum states of light in a silicon chip

02.07.2019 | Information Technology

Building trust in artificial intelligence – white paper for the certification of AI

02.07.2019 | Information Technology

Liquid crystal liver

02.07.2019 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>