Engineering coherent photons from semiconductor quantum dots

Abstract

Self-assembled semiconductor quantum dots (QDs) have great promise as quantum light sources due to their ability to generate single indistinguishable photons and entanglement. In this thesis, confocal microscopy experiments have been carried using non-resonant photoluminescence (PL) and resonant uorescence (RF) on QDs with the goal of characterising and developing them into high-quality quantum light sources. Through the application of uniaxial strain and an electric eld, single particle energies in a QD and their behaviour with strain are determined using a perturbative Coulomb blockade model. The exciton energy tuning magnitude is found to be a result of the near-cancellation of much larger single electron and hole tuning tuning. In addition, the rate of electron con nement energy tuning with strain is found to be correlated with the nominal unstrained con nement energy. An attempt is made at characterising the composition of the QDs through extracting deformation potentials, but the simple model does not capture the full system. Further, strain tuning of the ne structure splitting (FSS) of the neutral exciton X0 from QDs emitting at telecommunications wavelengths is shown. FSS tuning as large as 46 eV was observed, and using a phenomenological model select QDs were identi ed to achieve FSS < 1 ueV. RF is used to examine noise sources in QDs. Two sources of noise are considered: electric charge noise due to a uctuating charge environment, and nuclear spin noise due to the hyper ne interaction of single electron spins with a large number ( ~105) of nuclear spins. While the charge noise contributes to a loss in overall photon emission rates, but does not negatively impact the photon antibunching or indistinguishability at low Rabi frequencies, spin noise allows inelastic Raman scattering which reduces photon indistinguishability. The application of an external magnetic eld in the Faraday geometry screens the electrons from the nuclear spins, recovering a high degree of photon indistinguishability.