Anomalous enhancement of quasiparticle current near a potential barrier in a Bose-Einstein condensate

Abstract

We investigate tunneling properties of Bogoliubov phonons in a Bose-Einstein condensate. We find the anomalous enhancement of the quasiparticle current Jq carried by Bogoliubov phonons near a potential barrier, due to the supply of the excess current from the condensate. This effect leads to the increase of quasiparticle transmission probability in the low energy region found by Kovrizhin et al. We also show that the quasiparticle current twists the phase of the condensate wave function across the barrier, leading to a finite Josephson supercurrent Js through the barrier. This induced supercurrent flows in the opposite direction to the quasiparticle current so as to cancel out the enhancement of Jq and conserve the total current J=Jq+Js. DOI: 10.1103/PhysRevA.78.013628 PACS numbers: 67.85.De, 03.75.Kk, 03.75.Lm Phonon in a superfluid system is an example of Goldstone mode which appears in various fields of physics associated with spontaneous broken symmetry 1. It is a manifestation of broken global U1 symmetry which underlies the macroscopic quantum nature of the system, and a key to understand the low energy properties of superfluids. In particular, in a Bose superfluid, it plays fundamental roles for the superfluidity 2. Phonon has been observed in various systems such as superfluid 4 He 3, superconducting films 4, atomic superfluid fermi gases 5, as well as Bose-Einstein condensation BEC of cold atomic gases 6. Due to the high degree of controllability, BEC of cold atomic gases offers an opportunity to study properties of phonons in the superfluid phase.