Quantum fluid dynamics and superfluid behaviour of polaritons in microcavities

Achievement of polariton condensation in semiconductor microcavities [1,2] has opened the way to the study of new interesting phenomena related to the behaviour of non-equilibrium Bose particles in the quantum limit. In this talk we will see the formation of a coherent quantum state of polaritons created at a given momentum and at a given time using a combination of a continuous wave pump and a pulsed probe. This state is observed to persist in the cavity for a time much longer than the cavity lifetime [3]. Using this technique we are able to investigate the behaviour of a quantum state of polaritons with an extension of $\sim $ 20 $\mu $m moving a hundreds of microns within the cavity. One of the most striking effects of a moving polariton condensate is the observation of superfluid behaviour when crossing obstacles even at speeds only 100 times smaller than the speed of light [4]. Other interesting phenomena, which will be shown, are diffusion-less motion, due to the linearization of the polariton dispersion, and the formation of Cherenkov-like patterns for polaritons moving at supersonic velocities. \\[4pt] [1] J. Kasprzak et al. \textit{Nature} \textbf{443}, 409 (2006). \\[0pt] [2] R. Balili et al. \textit{Science} \textbf{316}, 1007 (2007). \\[0pt] [3] D. Ballarini et al. http://arxiv.org/abs/0807.3224 (arXiv:0807.3224) (2008). \\[0pt] [4] A. Amo et al. \textit{Nature}, forthcoming publication (2009).