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

Kónya, Gábor and Szirmai, Gergely and Domokos, Péter (2014) Damping of quasiparticles in a Bose-Einstein condensate coupled to an optical cavity. PHYSICAL REVIEW A, 90 (1). ISSN 2469-9926

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Abstract

We present a general theory for calculating the damping rate of elementary density wave excita- tions 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 damp- ing of a density wave mode, predicted recently by K´onya 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, both in the normal and 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.

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