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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    ABSTRACT: We study the second order temporal coherence of the emission from a semiconductor microcavity in the strong coupling regime. We evidence the favorable influence of spatial confinement, realized by etching micropillar structures, on the temporal coherence of solid state quasi-condensates which evolve in our device above threshold. By fitting the experimental data with a microscopic quantum theory based on a Monte Carlo wavefunction approach, we scrutinize the influence of the crystal lattice temperature (interaction with acoustic phonons) and pump power on the condensate's temporal coherence. Phonon-mediated transitions in the optical mode structure are observed, which in the case of a cofined structure splits into a set of discrete resonances. By increasing the pump power beyond the condensation threshold, the temporal coherence significantly improves in the pillar devices, as revealed in the transition from thermal to coherent statistics of the emitted light.
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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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    ABSTRACT: The theory for spontaneous coherence of short-lived quasiparticles in two-dimensional excitonic systems is reviewed, in particular, quantum wells (QWs) and graphene layers (GLs) embedded in microcavities. Experiments with polaritons in an optical microcavity have already shown evidence of Bose-Einstein condensation (BEC) in the lowest quantum state in a harmonic trap. The theory of BEC and superfluidity of the microcavity excitonic polaritons in a harmonic potential trap is presented. Along the way, we determine a general method for defining the superfluid fraction in a two-dimensional trap, within the angular momentum representation. We discuss BEC of magnetoexcitonic polaritons (magnetopolaritons) in a QW and GL embedded in an optical microcavity in high magnetic field. It is shown that Rabi splitting in graphene is tunable by the external magnetic field B, while in a QW the Rabi splitting does not depend on the magnetic field in the strong B limit.
    Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 12/2010; 368(1932):5459-82. DOI:10.1098/rsta.2010.0208 · 2.15 Impact Factor
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    ABSTRACT: The current status of research on exciton polaritons in semiconductor heterostructures with microcavities and the collective properties of polaritons under the conditions of Bose condensation are discussed.
    Semiconductors 07/2012; 46(7). DOI:10.1134/S1063782612070196 · 0.74 Impact Factor
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