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Title: Coherence properties of microcavity polariton condensates
Author: Bradley , Robert Andrew
ISNI:       0000 0004 2743 3586
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2012
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The polariton condensate is a highly interacting system with a macroscopically occupied state. Condensates may be formed either by non-resonant [1] or resonant (optical parametric oscillation) excitation [2] but the properties of the condensate are similar in bot.h cases. Due to the finite polariton lifetime, condensates are non-equilibrium. Nevertheless, they exhibit many of the same interesting phenomena as interacting Bose-Einstein condensates (BEC) in thermodynamic equilibrium, such as long-range spatial and temporal coherence and vortices. This thesis focusses on the coherence properties of polariton condensates within inorganic semiconductor microcavities. Condensates in CdTe microcavir ies excited using a non-resonant pump are shown to exhibit long coherence times of up to 250 ps, far longer than the polariton lifetime of "'" l.5 ps. This large slow-down in decay reveals intrinsic decohereuce properties which are confirmed by measuring the g(1) and g(2) correlation functions of single condensed modes. The characteristic lineshape of the 09(1) function is Gaussian. With increase of polaritons there is a "saturation" 3 in coherence time due to interactions, which has been predicted but not observed for equilibrium BEe. \Ye also demonstrate the existence of multiple, co-existing condensates which occur due to the non-equilibrium nature of the condensate. These condensates overlap in space and are shown to be truly independent of each other by correlation measurements. The condensates are triggered at momenta which are determined by the disorder of the polaritonic potential. Finally, the use of surface acoustic waves (SAW) to create a dynamic periodic potential is demonstrated. We study the effects of this potential on the condensate, such as the formation of condensate wires and corresponding reduction in spatial coherence due to reduced condensate dimensionality, We show that cont.rolled manipulation of coherence properties is possible, and discuss the potential for coherent transport. of the polariton condensate.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available