Research On The Enhancement Of Nonclassicality In Optomechanical Systems By Using Quantum Feedback

In recent years,the study of quantum phenomena in cavity optomechanical systems is one of the research topics in the field of quantum optics.The cavity optomechanical systems couples the cavity field and the mechanical oscillator via the radiation pressure,which provides a good platform for studying the quantum properties of the macroscopic system.By means of the optomechanical coupling,people can make use of the mature technology of quantum optics to control the quantum state of the mechanical oscillator,or use the mechanical oscillator to control the quantum properties of the cavity.On the other hand,the phenomenon of quantum decoherence caused by the inevitable coupling between systems and environment makes the quantum properties of the system weakens or vanishes.In order to enhance the quantum properties of the system,people can use quantum reservoir engineering and quantum feedback to achieve the quantum state with strong interference resistance in the system.Since it was put forward in 1930s,quantum nonlocality has been widely concerned and applied as an important research topic.Quantum nonlocality includes quantum entanglement,EPR quantum steering,and Bell non locality.It is one of the main differences between the quantum physics and the classical physics.It is also the resource for quantum information processing.In this paper,we introduce quantum feedback to enhance the nonclassical properties of the cavity optomechanical system.First of all,this paper briefly introduces the knowledge of cavity optomechanical systems,the criterion of quantum entanglement,quantum steering and Bell nonlocality for two-mode Gauss state.Then we study the two-mode cavity optomechanical systems with non-degenerate parametric amplifier(NDPA),and use quantum feedback to improve the entanglement and realize the EPR quantum steering and Bell nonlocality between two mechanical oscillators.The two cavity fields of the system forms a quantum entanglement due to the effect of NDPA,meanwhile the entanglement of the cavity field is transferred to oscillators because of the linear optomechanical mixing between the cavity field and mechanical oscillator,and the entanglement between the vibrators is formed.The maximum stable squeezing degree produced by NDPA can reach only half of the vacuum fluctuation compression,thus limiting the entanglement between the stable region vibrators,and the quantum steering is not shown between the vibrators at this time.In the stable region,We find that the quantum entanglement between two oscillators is greatly improved by introducing the quantum feedback based on the measurement,meanwhile the oscillators not only show the quantum steering at this time,but also has the Bell nonlocality,and under certain parameters conditions,we think that two oscillators are in an approximate two-mode squeezed vacuum state.The above numerical results are in agreement with the analytical results by adiabatic approximation.Secondly,we discuss that coherent feedback to enhance the squeezing of cavity output field in the system.The mechanical resonator(transparent thin film)is located in the middle of the cavity,and optomechanical coupling between the cavity and mechanical oscillator.The results show that the output field on the right side of cavity is directly fed back to the left side as the input field,and the coherent feedback have greatly enhanced the squeezing of the cavity output field without feedback.Whether there is time delay in the coherent feedback process or not,the cavity field squeezing can be greatly improved.