Tailored reservoir of exciton-polariton condensates

Abstract

The AlGaAs-like quantum wells sandwiched by high-quality microcavities can produce Wannier–Mott excitons and long-lifetime microcavity photons, forming the light-weight exciton-polaritons (polaritons) in the strong coupling regime. Polariton condensates can occur at cryogenic temperatures through optically excited high-energy excitons. Then the excitons follow a quick optical-phonon-induced relaxation into the reservoir, high-momentum of the lower polariton branch (LP). Through multiple scattering with acoustic phonons and parametric scattering in the vicinity of the LP bottleneck, the photonic components of the polaritons are increasing, and the polaritons on the reservoir eventually fall into the bottom or higher position of the LP, leading to the polariton condensates. The strong polariton-polariton interaction due to the excitonic components of the polaritons makes the polariton condensates a promising testbench for various nonlinear effects in the realm of quantum fluid of light. Through numerically solving the generalized Gross-Pitaevskii model coupled with the reservoir rate equation, this thesis studies methods to enhance and focus ballistic polariton condensates with tailored reservoir driven by localized nonresonant asymmetric-shaped excitation. This thesis demonstrates that the lens-shaped pump above the threshold can drive the focus of condensate away from the pumping region; by employing a second excitation next to the lens, the planar condensate flow is generated and can reflect and scatter with the lens-shaped blueshift, resulting in the focused condensate beating with hundreds of gigahertz. Furthermore, the source-lens system can be reprogrammed to achieve different beating locations and frequencies, paving the way for the realization of the all-optical transistor. This thesis also shows that in the polariton lattices, the stronger interaction between the nearest neighbors is achieved in the polygonal- rather than Gaussian-shaped pump due to the focused condensates flowing towards the nearest neighbors; and, in comparison to a Gaussian-shaped pump, the polygonal-shaped pump can increase the spatial coherence for a given power density or lower the energy needed for condensation. This finding can greatly improve spatial coherence in the needs of large-scale polariton condensates networks.

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Identifiers

ORCID for Yuan Wang: orcid.org/0000-0002-0688-3276

ORCID for Pavlos Lagoudakis: orcid.org/0000-0002-3557-5299

ORCID for Simone De Liberato: orcid.org/0000-0002-4851-2633

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