Phase-Resolved Imaging of Exciton Polaritons

In this PhD thesis, new imaging techniques have been developed in order to explore the physics of semiconductor microcavities. In these structures, composite bosons called exciton polaritons are the result of strong coupling between the cavity mode and quantum well excitons. A spectroscopic imaging technique has been developed to image the eigenstates of polaritons confined in the traps of a patterned GaAs microcavity. Polariton probability densities have been reconstructed in three dimensions – two spatial dimensions and energy – allowing to retrieve two-dimensional probability density mappings of the eigenstates. In order to image the wave functions (and not the probability densities only), a phase-resolved imaging setup has been built. Interfering the near field or far field of the polariton emission with a reference laser beam allowed to retrieve the full information (amplitude and phase) of the polariton wave functions. This tool allowed to evidence the effect of trap ellipticity on the confined polariton wave functions. Polariton vortices were also identified as a superposition of eigenmodes of the elliptical traps, and a selective excitation method has been used to optically control the sign and value of the vortex charge. Combining phase-resolved imaging with ultrafast optics allowed to probe the time evolution of coherent superpositions of confined polariton states. In particular, Rabi oscillations between vortex and anti-vortex states have been observed. Eventually, the time and phase resolved imaging tools have been used to explore the physics of quantum fluids. The scattering of polariton wave packets on a structural defect has been studied. Different flow regimes have been identified, and, in particular, quantum turbulence has been observed in the form of quantized vortices nucleating in the wake of the defect. The nucleation conditions have been established in terms of local fluid velocity and density on the obstacle perimeter. The results were successfully reproduced by numerical simulations based on generalized Gross-Pitaevskii equations.

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