The Influence And Suppression Of Excess Noise In Fiber Channel In Fiber-based Continuous Variable Quantum Information Processing

In the process of continuous variable quantum information processing,the quantum state light field is usually transmitted and distributed through quantum channels.Quantum channels include free-space channels and fiber channels.Free-space channels include ground-to-ground(i.e.atmospheric environment),ground-to-air(also through the atmosphere)and air-to-air.The main disturbance of the channel environment comes from atmospheric turbulence caused by various random factors,which causes the amplitude and phase fluctuations of the optical field.Random factors include buildings,weather conditions and even traffic,etc.The influencing factors of the channel environment are random and difficult to control.The fiber channel is highly compatible with the existing classical fiber communication system.It has the advantages of no electromagnetic interference,long relay distance and large transmission capacity,and is the best quantum channel for constructing metropolitan and intercity quantum networks.Telecommunication wavelengths of 1550 nm and 1342 nm correspond to the lowest loss and lowest dispersion window of fiber channel,respectively.The non-classical light fields of these two wavelengths are the ideal quantum light sources in quantum information processing over fiber.However,the decoherence effect caused by the interaction between the continuous variable quantum state field and the fiber channel is an unavoidable problem.In this paper,the influence and suppression methods of the excess noise in fiber channel in fiber-based continuous variable quantum information processing are investigated.Firstly,the influencing factors of the excess noise caused by guided acoustic wave brillouin scattering(GAWBS)effect in the fiber channel are studied and verified experimentally in the fiber channel with different distances.Then,the schemes of the local(LO)light being pulse modulated and frequency shift technology are used to suppress the excess noise of the fiber channel.The influence factors of the schemes on the suppression of the excess noise in the fiber channel are studied experimentally.The main research contents of this paper are as follows:1.Investigation on the excess noise of fiber channel in fiber-based continuous variable quantum information processing is carried out.The influence of the excess noise caused GAWBS is studied theoretically and experimentally.The scattering efficiency is calculated theoretically and verified experimentally in different distances of fiber channels.With the low power of LO and the short transmission distance of fiber,the scattering efficiency of GAWBS is consistent with the typical value.However,with the increasing of the LO power and transmission distance,GAWBS scattering efficiency increases.When the LO power is 3 m W and the transmission distance is 20 km,the scattering efficiency increases to 8 times greater than the typical value.2.The scheme of pulse modulated LO light is used to suppress the excess noise of fiber channel,and the influencing factors of this scheme on the suppression of excess noise of fiber channel are verified experimentally.The transmission distance of the squeezed vacuum state light field at 1550 nm with a squeezed degree of 3 d B is increased from 7 km to 15 km in single-mode fiber.3.The scheme of the frequency shift technology is used to suppress the excess noise of fiber channel,double-sideband frequency shift light is used as the LO light to suppress the excess noise of fiber channel,and the influencing factors of this scheme on the excess noise suppression of fiber channel are verified experimentally.The measured squeezed degree of the squeezed vacuum state light field transmitted over 1 km single-mode fiber is about 0.5 d B higher than that when the fundamental frequency light is used as the LO light.