Experimental Study On The Continuous Variable Quantum Key Distribution

As an alternative way for Quantum cryptography, Continuous Variables Quantum Key Distribution(CV-QKD) has attracted worldwide research interest. In a CV-QKD protocol, the quadrature variables of a coherent state which can be easily detected by homodyne detection are directly modulated to carry information.Here in the thesis we firstly introduce the rudimentary knowledge of quantum optics and information science, including the quantum optical states and information entropy. Then we illustrate the process of two CV-QKD protocols: Gaussian modulated CV-QKD protocol and four states protocol. In order to establish a secure key between two legitimate users, most of our efforts has been focused on experimental study on the implementing a real CV-QKD system. We design the experiment scheme and fabricate the homodyne detectors with high bandwidths. And by using the temperature control device, we achieve a very stable phase locking. Finally, at a repetition of 1MHz, we establish 32.8kb/s secure key rate in the optical fiber at the distance of 25 km. In the end, we investigate the possibility of transmitting both quantum signal and classical optical power in the same fiber. The coexistence architecture will increase the noise of the quantum channel. The cross phase modulation induced by classical traffic and its impact on the secure key rate are analyzed.