Bose Condensation and Lasing in Optical Microstructures - Part 1

TL;DR

This thesis explores the intermediate regime between polariton Bose-Einstein condensation and lasing, using many-body Green functions to analyze stability, decoherence effects, and distinguishability of condensates from lasers, with applications to quantum wires.

Contribution

It introduces a unified theoretical framework combining laser and condensate models, accounting for fermionic structure, decoherence, and dissipation in polariton systems, guiding experimental identification of condensates.

Findings

Identifies conditions for observing polariton condensates.

Provides criteria to distinguish condensates from lasers.

Develops a numerical method for excitonic properties in quantum wires.

Abstract

In the first part of this thesis I study the intermediate regime between ordinary lasing and a BEC of exciton polaritons. I take into account the fermionic structure of polaritons, treating the excitons as two-level systems coupled to a single mode in a microcavity. I introduce decoherence and dissipation processes to this system. Employing many-body Green function techniques, similar to those used by Abrikosov and Gor'kov in their theory of gapless superconductivity, I provide a mathematical structure that unifies models of lasers with models of condensates. This allows me to study the stability of the polariton condensate with respect to decoherence processes and the crossover between the polariton condensate and the laser. I give detailed indications of a regime in which the condensate should be observed to guide experimental work and show how to distinguish the Bose condensate from a laser. The second part of this thesis is concerned with properties of excitons and modelling of excitonic lasing in quasi-one-dimensional quantum wires. I develop a very general numerical method of calculating the properties of wires with different shapes and materials. Using this method I study the properties of very wide range of T-shaped quantum wires.