Frequency Downconversion Of Continuous Variable Quantum States

Quantum frequency conversion describes a process in which an input beam of light is converted into an output beam of a different frequency while maintaining the quantum states. Quantum frequency conversion can be used for creating tunable sources of squeezed light and getting some special wavelength that cannot be obtained directly by stimulated emission. It also served quantum interfaces between different nodes quantum networks. For example, it can achieve conversion between telecommunication wavelengths and quantum storage wavelengths for the lights carried quantum information so that nodes connect seamlessly. Quantum frequency conversion stimulated people’s strong research interest due to its important applications in the field of quantum information processing in recent years, and it has made great progress in theory and experiment especially in single photon’s frequency conversion.Continuous variable has become an effective means for quantum information processing and has been booming due to its high efficiency and unconditional limit in the preparation and detection of quantum states. This thesis mainly focus on the frequency down-conversion of continuous variable quantum states, including the following aspects:(1) A MgO-doped periodically poled LiNbO3 crystal was used to prepare a bright amplitude-squeezed light by an external cavity second harmonic generation.(2) The process of frequency down-conversion of continuous variable quantum states and factors affecting fidelity were theoretically analyzed. Then, quantum frequency high-fidelity down-conversion of prepared bright squeezed signal light from 532nm to 810nm was achieved experimentally by efficient resonant optical parametric down-conversion which was pumped by intense field at 1550nm.(3) The adverse effects on continuous variable’s quantum frequency conversion from the pump field’s extra amplitude and phase noise was investigated. In addition, a scheme for eliminating effects, utilizing twin resonant optical parametric down-convertors to eliminate amplitude noise and controlling the optimal pump power to eliminate phase noise, was proposed according to the theoretical analysis and was verified in experiment.