Experiments On Obtaining And Detecting The Squeezed State

The key problem in quantum communications is quantum state obtaining. Firstly, our primary study is how to obtain squeezed state, developing high-power, femtosecond-pulsewidth Cr4+ :YAG laser as the light source of squeezed state. We have optimized the cavity model of the laser, analyzed the mechanism of pulse mode-locking, discussed the mechanism of dispersion compensating using prism couples. Secondly, we have made an in-depth analysis on the obtaining mechanism and obtaining terms. Thirdly, we have studied the influences of gain and loss on the laser's oscillation threshold condition, absorption coefficient and pulse output characteristic. We have developed a new all-fiber scheme consist of femtosecond laser and Sagnac ring to obtain quantum state. We use a 2×2 broad-band fiber coupler with 90:10 splitting ratio to realize beam splitting and interfering, instead of film-coated glass in the air using by foreign experiments, and the squeezing is accoplished in all-fiber environment consquently. Our low-noise photodetector's 3dB bandwidth is 10MHz, saturation power is about 20mW and detecting efficiency is about 80%. We have got a 6.2dB squeezing taking the losses into account, and discussed the effects of fiber structure and lengths. In the first chapter of this thesis, we discuss the new trend of quantum communication. In chapter two, the Cr4+:YAG laser and the relative results are introduced. In chapter three, both quantum theory of optical pulse propagation in optical fiber and the basic thesis of squeezed state are studied. In chapter four, we firstly analyse the theory of photo-electrical detection. Secondly, we list three categories of photodetecters applied to our schemes. In chapter five, the scheme aimed to obtain soliton squeezed state is introduced. Meanwhile, we discuss corresponding results of all experiments.