Dicke模型中的量子相变近年来引起了人们很多的关注,而且在量子信息中有着非常重要的应用。Dicke模型研究N个二能级原子与单模电磁场相互作用,在电偶极近似下存在由正常相到超辐射相的二阶量子相变。 本文运用自旋相干态(SCS)变分法不仅考虑了场的电效应而且考虑磁效应所引起的量子相变,理论上发现了该系统中不仅存在Dicke模型中的二级量子相变而且还出现一级量子相变。在实验上,我们可以通过测量平均光子数或原子布居数来验证此类量子相变的发生。

Dicke model’s quantum phase transition,which has been applied extensively in quantum information,has attracted a lot of attention in recent years.Dicke model is used to study the interaction between N two-level atoms with the single-mode electromagnetic field.And it is the second-order quantum phase transition from the normal phase to the superradiation phase under the electrical dipole approximation.In this paper,the spin-coherent state (SCS) variation method is used to consider the quantum phase transition,which is induced by the electrical effect or the magnetic effect of the field.It was theoretically revealed that the system exhibits a novel first-order quantum phase transition in addition to Dicke-type second-order quantum phase transition,which can be verified by measuring the mean photon number or atom population difference.