Observation of Second Sound in a Quantum Gas

Second sound is a quantum mechanical phenomenon, which has been observed only in superfluid helium. Physicists from the University of Innsbruck, Austria, in collaboration with colleagues from the University of Trento and the National Research Council of Italy, have now proven the propagation of such a temperature wave in a quantum gas. The scientists have published their historic findings . Below a critical temperature, certain fluids become superfluid and lose internal friction. In addition, fluids in this state conduct heat extremely efficiently, with energy transport occurring in a distinct temperature wave. Because of the similarities to a sound wave, this temperature wave is also called second sound. To explain the nature of superfluids, the famous physicist Lev Landau developed the theory of two-fluid hydrodynamics in Moscow in 1941.