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We have used stress to create a harmonic potential for polaritons in GaAs microcavities and have previously reported that the polaritons undergo spontaneous coherence in the trap. In this paper we present results for both trapped conditions and resonant, nontrapped conditions in the same sample. We find that the results are qualitatively different with two distinct types of transitions. At low density in the trap, the polaritons remain in the strong coupling regime while going through the threshold for onset of coherence; at higher density, there is a different threshold behavior, which occurs with weak coupling and can be identified with lasing; this transition occurs both with and without a trap. The transition at lower density can therefore be identified as a type of nonequilibrium Bose–Einstein condensation. [ABSTRACT FROM AUTHOR]

We present a method for all-optical switching using a microcavity exciton-polariton system. Unlike many other switching methods, we use a single wavelength for both the signal and gate, which means that this method could be used for cascading optical logic gates and amplification within an all-optical circuit. We resonantly pump the sample at an angle with a laser beam and probe the sample with another beam at normal incidence. Upon saturation of the exciton-polariton states, the normal-incidence resonance increases in energy to permit the probe beam to be transmitted through the sample. Experimental results demonstrate switching using a GaAs/AlAs microcavity. Switching times on the order of ten picoseconds and on/off ratios on the order of 10:1 have been observed, and we propose design options to improve upon these. [ABSTRACT FROM AUTHOR]

Abstract: The theoretical and experimental status of the Bose–Einstein Condensation (BEC) of trapped quantum well (QW) polaritons in a microcavity is presented. The results of recent experiments that have shown the possibility to create an in-plane harmonic potential trap for a two-dimensional (2D) exciton polaritons in a cavity are discussed. We report the theory of BEC and of the trapped QW exciton polaritons in a microcavity. In addition, we study the BEC of trapped magnetoexciton polaritons in a graphene layer (GL) embedded in an optical microcavity in high magnetic field. In both cases the polaritons are considered to be in a harmonic potential trap. We compare the theoretical results with the existing experiments and discuss the experimental observation of predicted phenomena. [Copyright &y& Elsevier]