Designing Efficient Single-photon Sources for Quantum Information Application

This thesis, which consists of the theoretical studies, fabricating technologies, and experimental characterisation of quantum dots in microcavities, is a contribution to the debate on designing single quantum dots in micro-pillar microcavities as efficient single-photon sources for transmission of quantum information. First of all, I describe the basic concepts in quantum information science and technology. In addition to this, the design, simulation, modelling methods, fabrication technologies, and experimental measurement of single-photon sources for quantum information processing are briefly reviewed. I recall the basic notions of quantum optics, including confinement of electrons and photons in semiconductors, which are relevant to the properties and uses of single-photon sources. In Chapters 3 and 4 (the theoretical studies of quantum dots in microcavities), an attempt is made to present the approximation methods, such as the transfer-matrix model (TMM) and semi-analytic model, using an effective refractive index to calculate the guided fundamental HE11 cavity mode. I then focus on the 3-D finite-difference time-domain (FDTD) method used for the detailed investigation of design parameters for different types of microcavity geometries. These include circular and square pillars, radial trench distributed Bragg reflectors (DBRs), and quasi-3D photonic crystal defect microcavities. These last cavities are designed to further suppress transverse emission and leakage for generating efficient single photons on demand. I am also able to compare the calculated enhancements of spontaneous emission rates (Purcell factors) to those obtained from simpler approximations. In Chapter 5, attention turns to the focused ion beam (FIB) fabricating technologies and experimental characterisation of quantum dots in microcavities. I demonstrate a simple approach for the construction of single-photon sources utilising gas-assisted focused ion beam (GAE-FIB) etching to fabricate micro-pillar microcavities. Using the 1.5 µm square pillars, I demonstrate a single-photon source where the two photon emission is suppressed by a factor of 3.8. This has been confirmed using the Hanbury-Brown-Twiss (HBT) experiment. I believe this to be the first example of a FIB fabricated pillar single-photon source.