Optical control of polariton condensation and dipolaritons in coupled quantum wells
Baumberg, Jeremy J.
University of Cambridge
Department of Physics
Doctor of Philosophy (PhD)
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Cristofolini, P. (2015). Optical control of polariton condensation and dipolaritons in coupled quantum wells (Doctoral thesis). https://doi.org/10.17863/CAM.16617
Polaritons are lightweight bosonic quasiparticles that result from the strong coupling of light with an exciton transition inside a microcavity. A sufficiently dense cloud of polaritons condenses into a polariton condensate, a state of matter showing macroscopic coherence and superfluid properties, whose dynamics are influenced by the cycle of constant pumping and decay of polaritons. This thesis begins with an introduction on the particle and wave properties of the polariton condensate, followed by a theoretical description of two-dimensional Bose-Einstein condensation (BEC) and a section on simulation of polariton condensates. The optical setup and the microcavity sample are presented thereafter, including holographic laser shaping with a spatial light modulator (SLM), which allows exciting the microcavity with arbitrarily shaped pump geometries. Experimental results comprise optical control of polariton condensates, and dipolaritons. First, optical blueshift trapping and energy synchronisation (phase locking) of condensates are introduced. The transition from phase-locked condensates to an optically trapped condensate is investigated for a configuration of N pump spots arranged on a circle of varying diameter. Differences between these two condensate types are highlighted in the discussion section. Next, two parallel pump laser lines with small separation are investigated, which create a one-dimensional waveguide with strong uniform gain. Optically guided polaritons are investigated in this configuration with respect to coherence, flow speed, temperature and chemical potential. Observations hint that coherence arises below the condensation threshold simply from the chosen geometry of the system. The final chapter is dedicated to dipolaritons (polaritons with a static dipole moment) which form when polaritons strongly couple to indirect excitons in coupled quantum wells. In this system quantum tunnelling of electrons can be controlled with bias voltage. This allows tuning the dipolariton properties optically and electrically, with exciting prospects for future experiments. A conclusion and outlook section rounds off this work.
polariton, BEC, condensation, SLM, dipolariton, laser image, semiconductor spectroscopy, microcavity, optical control, flow dynamics
This record's DOI: https://doi.org/10.17863/CAM.16617
Attribution-NonCommercial 2.0 UK: England & Wales
Licence URL: http://creativecommons.org/licenses/by-nc/2.0/uk/
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