Theoretical And Experimental Study Of Continuous-Variable Quantum Key Distribution

Continuous-variable quantum key distribution is an important research direction in quantum information. This scheme can fully exploit the sideband of optical fields and has excellent noise suppression abilities. This thesis is a summary of my main work in this field during my PhD, and it contains six major topics as follows:1. Considering the noisy lasers and imperfect modulators in the real system, we analyzed the impact of the source noise to the security of the system, and derived a lower bound to the secret key rate.2. We made an experimental demonstration of four-state protocol continuousvariable quantum key distribution system. The no-switching scheme is adopted to improve the secret key rate.3. We built a fiber-based quasi-continuous-wave continuous-variable quantum key distribution system. Time and polarization multiplexing are both applied to fully suppress the channel cross-talk. No-switching scheme and broadband modulation are adopted to increase the secret key rate.4. To exploit multiplexing with other degrees of freedom, we studied optical vortices and generated beams with large optical angular momentum.5. We propose a scheme to generate Schr(?)dinger cat states with the size continuously tunable using nonlinear entanglement. The cat states can be used in continuous-variable quantum repeater. Also, we built an square optical cavity to enhance the weak nonlinear interaction.6. To extend continuous-variable quantum key distribution to the visible wavelength, we generated high power continuous-wave violet laser, and built an optical parametric amplifier of green beam, and realised the amplification and deamplification of green beam.