Generation Of Quantum Entangled States In Cavity Optical System

Quantum entanglement,as one of the most attractive research directions in quantum optics,can not only help people to understand some basic problems in quantum mechanics more deeply(such as quantum nonlocality,quantum decoherence mechanism,wave function collapse mechanism,etc.),but also are very important quantum resources in quantum computing,quantum information processing and constructing quantum networks.The continuous variable quantum entangled state light field has unique advantages in realizing quantum computing exponential acceleration,scalability and strong error correction ability.The traditional method of preparing continuous variable entangled state optical field is to use optical parametric process,which is mainly concentrated in optical frequency band,and it is difficult to extend to other frequency bands under the condition of energy conservation.In the constructed quantum network,quantum "nodes" with different frequencies are often encountered,which requires the preparation of entangled states that can connect different frequency systems.The mechanical oscillator in optomechanical system can be coupled with electromagnetic field in any frequency band,which makes it possible to prepare entangled states of electromagnetic field in different frequency band.We hope that we can find a reasonable scheme to produce continuous variable entangled state light field by optomechanical system on the basis of considering the actual experimental conditions,and study the parameter dependence of entanglement characteristics of output field.After that,a filter and beam splitter are added to the cavity of a two-pump cavity optical force system with the same frequency and different polarization.The output field of the filter can realize four-component entanglement after the beam splitter.This is of great value for the preparation of multi-component entanglement in practical experiments.The work accomplished in this thesis mainly includes the following contents:(1)The entanglement enhancement effect of output filtering in a special cavity optomechanical system is studied.when the frequency of the mechanical oscillator is half of the of the free spectral region of the cavity,only a single pump field can make the two longitudinal modes of the cavity interact with the mechanical oscillator at the same time,and the entanglement between the optical mode and the optical mode,the optical mode and the mechanical oscillator is robust.we study the entanglement between the two optical modes in the cavity after outputting the optical mode outside the cavity.the results show that there is still a steady state entanglement between the two optical modes after the filter output,and the larger entanglement can be obtained by optimizing the relevant filter parameters,which has important reference value for preparing and outputting the entangled state optical field in the actual experiment.(2)Based on the above-mentioned cavity optomechanics system,a scheme is proposed to produce the entangled light field of four consecutive variables.Using pump light with different polarization components,three component entanglement between two polarization double longitudinal modes and mechanical oscillator can be realized.After filtering output,four component entangled light field can be realized by coupling beam splitter.The dependence of entanglement structure on phase in beam splitter is further discussed.