Research On Quantum Entanglement And Improvement Based On Linear Devices Operation

In order to achieve various quantum tasks,it is usually necessary to prepare a quantum resource with higher entanglement.Therefore,how to enhance the entanglement of quantum states is a key issue.In addition to common non-Gaussian operations such as photon addition and photon deduction,quantum scissors(SSQS),first proposed by Pegg et al.in 1998,is also a feasible strategy to increase entanglement.The results show that for an input coherent state,the obtained state can be truncated into a superposition of a zero-photon state and a single-photon state.Can this squeezing-based quantum scissors improve the entanglement of two-mode squeezed vacuum state(TMSV)? The following aspects are the specific research contents of this paper.Firstly,The entanglement improvement is theoretically investigated when applying a single-side SSQS with a local squeezing operation and two-asymmetrical beam splitters(BSs)to one mode of an input TMSV.It is found that the gain factor can be significantly enhanced with the increasing of local squeezing parameter at the expense of the success probability.The entanglement can also be further improved adjusting the local-squeezing or the transmissivity of BSs in a small initial squeezing region.In addition,our scheme is robust against the photon loss in TMSV.The improved effect becomes more obvious due to the presence of local squeezing.However,the case is not true for a more realistic SSQS.In both cases,the asymmetric BSs play a positive role for the entanglement improvement.These results suggest that the squeezing-based SSQS at single-photon level is beneficial to effectively improve the entanglement,which may have potential applications in quantum communication.Secondly,Typically,non-Gaussian operations are simulated by a beam.A beam splitter operator is a very important linear device in the field of quantum optics and quantum information.It can not only be used to prepare complete representations of quantum mechanics,entangled state representation,but it can also be used to simulate the dissipative environment of quantum systems.In this paper,by combining the transform relation of the beam splitter operator and the technique of integration within the product of the operator,we present the coherent state representation of the operator and the corresponding normal ordering form.Based on this,we consider the applications of the coherent state representation of the beam splitter operator,such as deriving some operator identities and entangled state representation preparation with continuous-discrete variables.Furthermore,we extend our investigation to two single and two-mode cascaded beam splitter operators,giving the corresponding coherent state representation and its normal ordering form.In addition,the application of a beam splitter to prepare entangled states in quantum teleportation is further investigated,and the fidelity is discussed.The above results provide good theoretical value in the fields of quantum optics and quantum information.