Superfluidity and Bose-Einstein Condensation Coherence (Prof. Dr. Lev Pitaevskii)
Oct 16, 2018
13:30 - 15:00
Prof. Dr. Lev Pitaevskii
University of Trento & P.L. Kapitza Institut for Physical Problems, Moscow
Max-Planck-Institut für Quantenoptik
Hörsaal, Raum B 0.32 / New lecture hall, Room B 0.32
MPQ, Laser Spectroscopy Division
In 1938 Petr Kapitza, investigating properties of the low temperature phase of liquid 4He, discovered that viscosity of the liquid is more than 104 times smaller, than that of all known liquids. Kapitza concluded, that the liquid is in a new state of matter, a “superfluid”, which to some extend analogous to superconductors. Landau (1941) explained the phenomenon and predicted several its unusual properties. It occurs, that in a superfluid in any point of space at finite temperatures simultaneously exists two flow with different velocities. One is “normal” and has finite viscosity and the second one is “superfluid”, which viscosity is exactly zero. This results in presence of two type of sound, which were discovered experimentally in 1946.
Even more striking phenomena exist in rotating
superfluid. A normal, usual liquid in a rotating vessel rotates as a solid body
and its surface takes shape of well-known meniscus. It was suggested by Onsager
(1949) and Feynman (1954) that a superfluid rotates around of singular quantum
vortexes in such a way that the circulation of velocity of a superfluid around
a vortex is quantized. It gives possibility to measure the Planck constant in a
simple mechanical experiment.
Another quantum state of matter – the Bose-Einstein
condensation – was predicted by Einstein in 1925 and discovered in 1995 by
Cornell, Wieman and Ketterle.
Bose-Einstein condensed gases are superfluid and, as was shown by Bogolyubov
(1947), a microscopic theory can be developed in great detail due to the
weakness of interaction. Many phenomena can be described in the mean-field
approximation by the so called Gross-Pitaevskii theory.
A new possibility were open by creation of strongly
interacting, but still dilute, superfluid Fermi liquids.