Ultrapure Single Photons And Spin-photon Entanglement From Self-assembled Quantum Dots

In the thesis, we have discussed the deterministic and robust generation of pulsed resonance fluorescence single photons, Raman photons and spin-photon entanglement. The main results are as follows:1. we have demonstrated the on-demand generation of near background-free (～99.7%purity) and highly indistinguishable RF single photons from a quantum dot in a planar microcavity driven by resonant π pulses. The RF photons show an antibunching of f2(0)=0.012(2). Non-postselective HOM two-photon interference has revealed near-unity visibilities (～97%). Our work on so-called s-shell pulsed excitation in quantum dots is the first to go beyond the previous record holding p-shell pulsed excitation technique developed10years ago by Yoshihisa Yamamoto’s team at Stanford Uni-versity. This is the first work in the field of quantum dot related optical quantum control published in "Nature" series for the research groups in China.2. We demonstrate deterministic and robust generation of pulsed resonance fluorescence single photons from a single InGaAs quantum dot using the method of rapid adiabatic passage. The generated single photons are back-ground 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%), reaching a precision that places single photons at the threshold for fault-tolerant surface-code quantum computing.3. All-optically tunable and highly indistinguishable single Raman photons from a driven single quantum dot spin are demonstrated. The frequen-cy, linewidth, and lifetime of the Raman photons are tunable by varying the driving field power and detuning. Hong-Ou-Mandel interference is demon-strated between two single photons emitted from remote, independent quan-tum dots with an unprecedented visibility of0.87(4).4. The first observation of GHZ type entanglement in a single quantum dot is demonstrated. The measurements of reconstructed electron-spin, photon-frequency, photon-polarization entangled states(GHZ) confirm the conflict between quantum mechanical and local realistic predictions in the solid-state platform.5. We report the first experimental demonstration of interference induced spec-tral line elimination and dynamical suppression of spontaneous emission. Our achievement provides a versatile knob to control and modulate the spontaneous emission process and open the way to obtain spectral line nar-rowing.