Optical Performance Of Quantum Dots Based On Cavity Quantum Electrodynamics

Within the field of quantum computation and quantum communication,a key compo-nent is the on-demand single-photon source(SPS)of high quality.To estimate its quality,there are three figures of merit:purity,to estimate if the photon distribution of the photon source satisfies the single-photon distribution;indistinguishability ?,to guarantee efficient interference between photons;efficiency ?,defined as the collected photons after each ex-citation trigger.At present,quantum dot(QD)embedded in the host material,since it could be easily integrated to semiconductor photonics,has emerged as a promising plat-form for scalable optical quantum information processing.However,for the QD in bulk material,due to the high index contrast in the semiconductor-air interface,its efficiency is limited to?0.03.To improve the collection efficiency,much effort has been devoted into enhancing the Purcell effect in the literature.Design scheme includes the broadband structures-the photonic nanowire and the circular-brag-grating cavities,as well as the nar-rowband structures-the micropillar and the Hour-glass structures.At present,there are several methods that could be applied to calculate the electromagnetic field distribution from the QD in the cavity,including the finite-difference time-domain method,the finite element method,the Green's function integral equation method and the Fourier Modal method.Since the Fourier Modal method could naturally separate the cavity mode with the other background mode,it is convenient to use this method to investigate the back-ground governing physics to the emission mechanism in photonic structures.Then,as for the indistinguishability,the noise in the environment around the QD-cavity mode system,such as the phonon scattering,induces the dephasing of the emitted photons,leading to a low indistinguishability.The standard method to investigate this problem relies on the master equation in the open quantum system.In this thesis,we respectively apply the Fourier Modal method and the master equation to perform a numerical investigation of the efficiency and indistinguishability,in order to improve the performance of the QD SPS.At the beginning of this dissertation,the background information about the QD SPS,the numerical method to get access to the efficiency and the calculation of the indistin-guishability are first introduced respectively in each chapter.Specifically,in Chapter 1,we first introduce the growing method and the emission features of the QDs.Then,we introduce the definition as well as the experiment measurements of the three figures of merit of the SPS-purity,efficiency and indistinguishability.In Chapter 2,we present the introduction of the optical modeling via applying the Fourier Modal method to get access to the field distribution in microcavities as well as the efficiency.Then,in Chapter 3,the microscopic modeling to calculate the indistinguishability of QD SPSs is introduced.Specifically,we show the method to calculate the reduced density matrix of the QD-cavity mode system at the presence of phonon induced scattering.The modeling methods men-tioned above provide the base of our simulation for the specific problems.In Chapter 4,in the presence of non-Markovian phonon-induced decoherence,we present the numerical investigation of the performance of the micropillar cavity single-photon source in terms of collection efficiency and indistinguishability of the emitted pho-tons.We analyze the physics governing the efficiency using a single-mode model,and we optimize efficiency ? and the indistinguishability ? on an equal footing by computing ??as function of the micropillar design parameters.We show that ?? is limited to?0.96 for the ideal geometry due to an inherent trade-off between efficiency and indistinguishability.Finally,we subsequently consider the influence of realistic fabrication imperfections and Markovian pure dephasing noise on the performance.In Chapter 5,we optimize the efficiency of a quantum-dot-based micropillar single-photon source by minimizing the spontaneous emission into unwanted background modes.We perform a numerical investigation of the background emission in infinite nanowire and in micropillar,where we identify a semi-periodic enhancement with diameter.At these peaks of the background emission,the efficiency is reduced by?20%,and we show how this reduction can be avoided simply by choosing a diameter away from the peaks.Finally,we analyze the discrepancy between the Purcell factor estimated from experimental lifetime measurements and the true Purcell factor.