Intrinsic Decoherence Mechanisms in the Microcavity Polariton Condensate

Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, United Kingdom.
Physical Review Letters (Impact Factor: 7.51). 09/2008; 101(6):067404. DOI: 10.1103/PhysRevLett.101.067404
Source: PubMed


The fundamental mechanisms which control the phase coherence of the polariton Bose-Einstein condensate (BEC) are determined. It is shown that the combination of number fluctuations and interactions leads to decoherence with a characteristic Gaussian decay of the first-order correlation function. This line shape, and the long decay times ( approximately 150 ps) of both first- and second-order correlation functions, are explained quantitatively by a quantum-optical model which takes into account interactions, fluctuations, and gain and loss in the system. Interaction limited coherence times of this type have been predicted for atomic BECs, but are yet to be observed experimentally.

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    • "Analogous to a conventional laser operating in the weak coupling regime (for instance the vertical cavity surface emitting laser, VCSEL), the formation of a BEC of polaritons is accompanied by a nonlinear increase of the intensity of the emitted light and a drop of the spectral linewidth [2].The latter is a typical, yet not unambiguous signature of first order temporal coherence of the emitted radiation . A more sophisticated approach relying on Michelson interferometry was discussed in [5], where strongly enhanced coherence times in the regime of polariton lasing have been demonstrated by using low noise pump sources. In analogy to cold atom BECs, the first order spatial coherence (long range order), has been considered as a smoking gun criterion for the claim of a polariton BEC [6] [7] [8] [9]. "
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    • "In a translationally invariant two-dimensional system, without a trap, superfluidity occurs via a Kosterlitz–Thouless superfluid (KTS) transition. Experiments on untrapped systems (Deng et al. 2002, 2003, 2006; Kasprzak et al. 2006; Baumberg et al. 2008; Love et al. 2008) have shown promising indications of the onset of spontaneous coherence effects. In principle, superfluidity in a finite two-dimensional system can be viewed as a type of BEC, with coherence length of the order of the size of the cloud of particles, what is sometimes called a 'quasicondensate' (Malpeuch et al. 2003). "
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