Generation Of Atomic Schr(?)dinger-cat States Via Non-hermitian Quadratic Interactions

The Schr(?)dinger cat state is a hot research topic in the field of quantum optics in recent years.It refers to a macroscopically distinguishable quan-tum superposition state.It is an important non-Gaussian entangled state,which can be used in quantum precision measurement,quantum commu-nication,quantum computing,etc.;The multi-particle “Schr(?)dinger cat”states system can be used as a core component of future high-fault-tolerant quantum computers,and can also be used to make extremely sensitive sen-sors and precision measurement equipment such as atomic clocks,grav-itational wave detection,interferometers,etc.;the Schr(?)dinger cat state is considered to be the best entanglement resource for noise-free quantum metrology.Therefore,studying the properties of Schr(?)dinger cat states and their preparation methods has become a frontier topic that attracts academic circles.However,due to their highly entangled nature of multi-particles,the resulting states are extremely fragile.A single error on any sub-system may cause the collapse of the macroscopic superposition state,which poses a severe challenge to the creation of a cat state containing a large number of particles.This paper mainly studies the Schr(?)dinger cat state of atoms produced by non-Hermitian quadratic interactions in a two-level atomic system.The main research contents are as follows:1.The study of using non-Hermitian quadratic nonlinear interactions to produce atomic Schr(?)dinger cat states in the atomic ensemble.At present,the general scheme for generating Schr(?)dinger cat states is through nonlin-ear unitary evolution or measurement of related auxiliary(interacting with atoms)quantum systems.The non-Hermitian interactions of quantum sys-tems are generally considered to cause the dissipation and decoherence of the system,and are usually regarded as the main factor that destroys the co-herence of atoms,so they are unnecessary.However,this study found that non-Hermitian quadratic interactions can be used to efficiently prepare the Schr(?)dinger cat state of atomic ensemble.At the same time,we have also considered the method of achieving non-Hermitian quadratic interactions,which can be achieved by unitary one-axis twisting and non-Hermitian lin-ear evolution.Preliminary estimates indicate that even under the existing experimental conditions,our scheme can also prepare the Schr(?)dinger cat state of the large atomic number system.2.Research on the properties of many-body entanglement generated in the atomic ensemble under the Hermitian quadratic nonlinear interaction.So far,for one-axis twisting evolution,most studies have focused on the spin compression of atomic systems,and few works have focused on the multi-body entanglement properties of atomic systems under this unitary evolution.This paper studies the multi-body entanglement characteristics of the system under the quadratic interaction,and also considers the char-acteristics of the multi-body entanglement evolution of the system after the presence of the linear interaction term.Through the study,we find that the multi-body entanglement of the spin system maintains much longer when the linear and nonlinear interactions are combined.Moreover,we consid-ered the entanglement process of the system under the influence of noise,and found that even in the presence of noise,the atomic system still has a high degree of entanglement.