title: Spin squeezing as an indicator of quantum chaos in the Dicke model.
abstract: We study spin squeezing, an intrinsic quantum property, in the Dicke model without the rotating-wave approximation. We show that the spin squeezing can reveal the underlying chaotic and regular structures in phase space given by a Poincaré section, namely, it acts as an indicator of quantum chaos. Spin squeezing vanishes after a very short time for an initial coherent state centered in a chaotic region, whereas it persists over a longer time for the coherent state centered in a regular region of the phase space. We also study the distribution of the mean spin directions when quantum dynamics takes place. Finally, we discuss relations among spin squeezing, bosonic quadrature squeezing, and two-qubit entanglement in the dynamical processes.
authors.affiliation: Institute of Applied Physics, School of Science, Changchun University, Changchun 130022, People's Republic of China.
authors.forename: Lijun
authors.initials: L
authors.lastname: Song
authors.forename: Dong
authors.initials: D
authors.lastname: Yan
authors.forename: Jian
authors.initials: J
authors.lastname: Ma
authors.forename: Xiaoguang
authors.initials: X
authors.lastname: Wang