| Quantum information science is formed by combining the basic theory of quantum mechanics with information science and technology.As an important quantum resource,nonclassical quantum states play an important role in the basic theoretical research and experimental technology development of quantum information science.The four-wave mixing(FWM)process based on the atomic ensemble is one of the effective methods for preparing nonclassical quantum states due to its strong nonlinearity,spatial multimode nature and low-noise amplification property.Therefore,based on the FWM process in a hot rubidium atomic cell,this thesis focuses on constructing ultra-largescale(ULS)quantum entanglement and enhancing the quantum correlation in continuous-variable(CV)system.The following three parts are mainly introduced: 1.The scheme for generating an ULS CV entanglement containing 2×N optical modes based on a time-delayed SU(1,1)quantum interferometer is theoretically proposed.In this scheme,the first FWM process of the SU(1,1)quantum interferometer serves as the entangled source.Then,a time-delayed line is introduced in one of the two arms of the quantum interferometer,which realizes the function of time multiplexing.Finally,the secondary FWM process of the SU(1,1)quantum interferometer is utilized to realize the combination of the time-delayed entangled beams.As a result,an ULS CV quantum entanglement of 2×N modes is generated from such time-delayed SU(1,1)quantum interferometer.This theoretical result verifies the feasibility of exploiting SU(1,1)quantum interferometer to generate ULS quantum entangled states experimentally.2.The scheme for generating an ULS CV deterministic entanglement containing2×20400 optical modes based on a time-delayed SU(1,1)quantum interferometer is experimentally demonstrated.During the experimental process,a time-delayed line was prepared by introducing a fiber into one of the two arms of the SU(1,1)quantum interferometer to generate 2 ×20400 optical wave packets.The information of amplitude quadrature and phase quadrature of each wave packet is obtained by balanced homodyne detection technique.In the processing of experimental results,these wave packets are divided into 20399 wave packet units.Firstly,the positivity under partial transposition criterion is used to verify the entanglement characteristics of all the wave packet units.Then,by retrieving the eigenmodes from the covariance matrix,it is found that each wave packet unit is indeed composed of four independent squeezed modes.Therefore,the generated ULS entangled states contain 81596 squeezed modes.Furthermore,we verify the consistency of the eigenmode squeezing levels for all the wave packet units.Because of the large scale and deterministic generation method,the ULS CV quantum entanglement could find applications for implementing ULS CV quantum information processing.3.The scheme for the enhancement of intensity-difference squeezing using a phase-sensitive cascaded FWM processes in a rubidium atomic vapor cell was proposed theoretically and experimentally demonstrated.Firstly,it is theoretically studied and experimentally verified that the single FWM process has the characteristic of intensitydifference squeezing.Secondly,the intensity-difference squeezing between the three output beams generated by the phase-sensitive cascaded FWM processes is compared with the phase-insensitive cascaded FWM processes theoretically and experimentally.The results show that the intensity-difference squeezing between the three output beams generated by the phase-insensitive cascaded FWM processes can be greatly enhanced by introducing a phase-sensitive cascade FWM processes.When the interference phase of phase-sensitive FWM process is locked at 0,the intensity-difference squeezing between the three output beams generated by the phase-sensitive cascaded FWM processes reaches a maximum.This scheme demonstrates a new method for achieving the enhancement of quantum squeezing and may find potential applications in quantum precision measurement. |
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