Lecture: Damping of quasiparticles in a Bose-Einstein condensate coupled to an optical cavity

22.02.2017, 11:00

Dr. Gergely Szirmai, Wigner Research Center, Budapest, Hungary

 

Time, place:

Wednesday, 22nd February 2017, 11:00h
Seminar Room A1.500, MPL, Staudtstr. 2, 91058 Erlangen


Abstract:

We present a general theory for calculating the damping rate of elementary density-wave excitations in a Bose-Einstein condensate strongly coupled to a single radiation field mode of an optical cavity. Thereby we give a detailed derivation of the huge resonant enhancement in the Beliaev damping of a density-wave mode, predicted recently by Kónya et al. [Phys. Rev. A 89, 051601(R) (2014)]. The given density-wave mode constitutes the polariton-like soft mode of the self-organization phase transition. The resonant enhancement takes place in both the normal and the ordered phases, outside the critical region. We show that the large damping rate is accompanied by a significant frequency shift of this polariton mode. Going beyond the Born-Markov approximation and determining the poles of the retarded Green's function of the polariton, we reveal a strong coupling between the polariton and a collective mode in the phonon bath formed by the other density-wave modes.