Visualising Berry phase and diabolical points in a quantum exciton-polariton billiard
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Diabolical points (spectral degeneracies) can naturally occur in spectra of two-dimensional quantum systems and classical wave resonators due to simple symmetries. Geometric Berry phase is associated with these spectral degeneracies. Here, we demonstrate a diabolical point and the corresponding Berry phase in the spectrum of hybrid light-matter quasiparticles – exciton-polaritons in semiconductor microcavities. It is well known that sufficiently strong optical pumping can drive excitonpolaritons to quantum degeneracy, whereby they form a macroscopically populated quantum coherent state similar to a Bose-Einstein condensate. By pumping a microcavity with a spatially structured light beam, we create a two-dimensional quantum billiard for the exciton-polariton condensate and demonstrate a diabolical point in the spectrum of the billiard eigenstates. The fully reconfigurable geometry of the potential walls controlled by the optical pump enables a striking experimental visualisation of the Berry phase associated with the diabolical point. The Berry phase is observed and measured by direct imaging of the macroscopic exciton-polariton probability densities.
Estrecho , E , Gao , T , Brodbeck , S , Kamp , M , Schneider , C , Höfling , S , Truscott , A G & Ostrovskaya , E A 2016 , ' Visualising Berry phase and diabolical points in a quantum exciton-polariton billiard ' Scientific Reports , vol 6 , 37653 . DOI: 10.1038/srep37653
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This work is supported by the Australian Research Council and the State of Bavaria.
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