Room-Temperature Bose-Einstein Condensation of Exciton-Polaritons in Photonic Crystal Architectures
Year: 2018
Type: dissertation
Abstract: Bose-Einstein condensation (BEC) is a remarkable manifestation of quantum mechani- cal behaviour where a macroscopic number of particles occupy a single particle ground state. Typical realizations of BEC occur at temperatures close to absolute zero. In this thesis, we propose a route towards full thermal equilibirum, room-temperature BEC of “half-light” - “half-matter” quasiparticles known as exciton-polaritons. Our proposed strategy uses three-dimensional photonic crystals to form the optical resonator; this leads to long lived confined optical modes. These long lived confined optical modes allow the condensates to reach full thermal equilibrium. Photonic crystal resonators ensure that the light-matter coupling strengths are significantly stronger than in conventional archi- tectures; this leads to BEC formation at higher temperatures. A central quantity in our work is the (lower) exciton-polariton dispersion depth. The dispersion depth is an energy scale that governs the limit on the critical temperature. Strategies for increasing the dispersion depth to facilitate room-temperature BEC will be discussed. We first examine exciton-polariton BEC in optical resonators composed of slanted pore photonic crystals. We consider InGaAs/InP quantum wells embedded in the res- onator to allow for light emission at a wavelength of approximately 1300 nm. In esti- mating the critical temperature, we ensure the use of modest exciton-polariton densities to avoid the saturation of the exciton resonance. Using three quantum wells, our study reveals that exciton-polariton BEC occurs for temperatures above 300 K and that our results are robust to both photonic and electronic disorder. Next, we investigate exciton-polariton BEC in optical resonators composed of wood- pile photonic crystals. We treat GaAs/AlAs quantum wells embedded in resonator to allow for the emission of light with a wavelength of approximately 750 nm. Due to the x-y symmetry of the woodpile photonic crystal, the exciton-polariton ground state exhibits a two-fold polarization degeneracy. We show that symmetry breaking lifts the degeneracy of the ground state and results in larger critical temperatures and higher condensate fractions, in comparison to a symmetrical woodpile structure. Our results show that for three quantum wells and a moderate exciton-polariton density that a BEC can be obtained at temperatures over 300 K; this condensate is robust to disorder.
Source: TSpace (University of Toronto)
Author: Pranai Vasudev
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W3081840842