Quantum Fisher Information And Spin Squeezing Of The Non-hermitian One-axis Twisting Model And The Effect Of Dephasing

In this thesis,we focus on the non-Hermitian twisting model,and investigate the quantum Fisher information and spin squeezing of non-Hermitian twisting model in detail.On top of that,we study the effect of dephasing which is caused by external field fluctuations.Firstly,we review the fundamental knowledge including entanglement,spin squeezing states.In particular,we introduce the main methods that are used to generate spin squeezing states.The two methods are one-axis twisting model and two-axis countertwisting model.Secondly,we review the features of non-Hermitian system,the characters of steady state.Especially we introduce the spin squeezing of non-Hermitian one-axis twisting model,and the entanglement and averaged quantum Fisher information of two-axis countertwisting model.As the main content of this thesis,a detailed analysis of the quantum Fisher information(QFI)and spin squeezing(SS)of the non-Hermitian one-axis twisting model is conducted in chapter 4.The results show that non-Hermitian model achieves significant entanglement in many-body systems,which is quite different from the Hermitian case.As for spin squeezing,non-Hermitian model can achieves more SS than the optimal value of the Hermitian counterpart.For appropriate parameters,the non-Hermitian OAT model can achieve optimal spin squeezing ζ2≈3/N which is obviously better than that of the Hermitian OAT counterpart and slightly better than that of the Hermitian TACT model.Furthermore,we investigate the effect of dephasing which is induced by external field fluctuations,and find out to what extent it weakens QFI and SS of the non-Hermitian one-axis twisting model.