Experiments On Quantum Communications

Quantum informatics is a rising interdiscipline of informatics and quantum mechanics. Quantum communication is an important branch of quantum informatics, which has advantages in improving the arithmetic speed, ensuring the security of information, increasing data capacity and improving information accuracy.In this paper, two parts are mainly focused on, one for the quantum squeezing state obtaining and detecting experiment, the other for the continuous variable quantum key distribution experiment.First, the basic theory and progress of squeezing state is introduced. Based on the quantum theory of light field, the basic state of quantum light field - coherent state, is studied. Further more, based on the Heisenberg uncertainty relation, the characteristics of squeezing state is studied. One of the two orthogonal quadrature of the light field is lower than the uncertainty limits, while the other is higher than the limit, but their product is greater than or equal to the uncertainty limits. Finally, the progressed of theoretical and experimental study on squeezing state is summarized.Based on the study on squeezing state, an experiment scheme for obtaining and detecting soliton amplitude squeezing light is designed. The optical signal detection theory is studied, according to the characteristics of squeezing state, photodetector it for squeezing state detection is designed. The 3 dB bandwidth of the detector is measured to be 10 MHz, the noise equivalent power is about 6pW/Hz^1/2, and the saturation power is about 19 mW, the performances can meet the need for quantum squeezing state detection.An experiment scheme for obtaining and detecting squeezing state is studied. Soliton amplitude squeezing state is obtained using asymmetric Sagnac interferometer and detected using balanced homodyne detecting system. A maximum photocurrent noise reduction of 5dB below shot noise is achieved. The whole system is achieved in an all-fibre environment, which makes the system integration more realizable.Finally, the basic theory of quantum key distribution is introduced, and the BB84 protocol for quantum key distribution is mainly studied. Based on BB84 protocol, a continuous variable quantum key distribution experiment system is designed, the balanced homodyne detection system in the system is focused on. Because the signal in the continuous variable quantum key distribution experiment system is weak, and the triggering time is short, the photoelectric detector circuit is improved to meet the need of the system.