Generation And Coherence Of High-Quality Quantum-Dot Single Photons

Single-photon and entangled photons sources have promising applications in the field of quantum information, such as quantum key distribution and linear optical quantum computation. Semiconductor quantum dot being called artificial atom is a nanostructure that confines electrons and holes, leading to discrete energy levels. It can be used to generate single photons and entangled photon pairs. In this thesis, we mainly study single photon generation from a single In(Ga)As/GaAs self-assembled quantum dot. Self-assembled quantum dots have excellent photonic properties. The linewidth of their emitted photons is ability to be radiative lifetime limited. Furthermore, using semiconductor heterostructure and post-growth processing techniques, the interaction between quantum dots and light as well as quantum dot charge state can be controlled.We have developed resonance fluorescence technology in experiment. Com-bining this technology with frequency filter, we have realized pure on-demand semiconductor single-photon sources with high quality. A second-order correla-tion measurement indicated that the probability of multi-photons generation is only1.2%. A Hong-Ou-Mandel two-photon interference experiment reveals that degrees of indistinguishability of these photons approaching to97%, much larger than that of above band (incoherent) excitation generated quantum dot single photons which have degrees of indistinguishability with70%. Based on these,we have demonstrated deterministic and robust generation of pulsed resonance fluo-rescence single photons from a single quantum dot using the method of adiabatic rapid passage. The trion state in quantum dot is excited with a chirped pulse and its population is insensitive to the fluctuation of laser power at low temperature. The generated single photons are background free, have a vanishing two photon emission probability of0.3%and a raw (corrected) two-photon Hong-Ou-Mandel interference visibility of97.9%(99.5%). These robust single photon sources have potential applications in linear optical quantum computation, such as being scaled to multi-photon entanglement.We have also studied temperature effect on the quantum coherence proper-ties of quantum dot in experiment. Preserving the coherence of quantum state is very crucial to quantum, dots’applications in quantum information processing and quantum communication. Both fidelity of quantum operation and visibility of quantum interference depend on the ability of quantum systems to keep their coherence in a long time. The excited state will dephase due to scattering of quantum dot with phonons in the surrounding, leading to broaden of emission linewidth. We have measured the linewidth of Mollow triplet sidebands at dif-ferent temperature and found that due to interaction between quantum dot and phonons, Rabi frequency is renormalized and effective Rabi frequency is relative to temperature. We have also first observed that sidebands linewidths are little changed with the temperature variation. This founding has important significance for quantum dots’ applications in quantum information.