We investigate how displaced thermal states （DTSs） evolve in a laser channel. Remarkably, the initial DTS, an example of a mixed state, still remains mixed and thermal. At long times, they finally decay to a highly classical thermal field only related to the laser parameters κ and g. The normal ordering product of density operator of the DTS in the laser channel leads to obtaining the analytical time-evolution expressions of the photon number, Wigner function, and von Neumann entropy. Also, some interesting results are presented via numerically investigating these explicit time-dependent expressions.
Extending the recent work completed by Fan et al. [Front. Phys. 9（1）, 74 （2014）] to a two-mode case, we investigate how a two-mode squeezed vacuum evolves when it undergoes a two-mode amplitude dissipative channel, with the same decay rate ~, using the continuous-variable entangled state approach. Our analytical results show that the initial pure-squeezed vacuum state evolves into a definite mixed state with entanglement and squeezing, decaying over time as a result of amplitude decay. We also investigate the time evolutions of the photon number distribution, the Wigner function, and the optical tomogram in this channel. Our results indicate that the evolved photon number distribution is related to Jacobi polynomials, the Wigner function has a standard Gaussian distribution （corresponding to the vacuum） at long periods, losing its nonclassicality due to amplitude decay, and a larger squeezing leads to a longer decay time.
Xiang-Guo MengJi-Suo WangBao-Long LiangCheng-Xuan Han
We solve the fermionic master equation for a thermal bath to obtain its explicit Kraus operator solutions via the fermionic state approach. The normalization condition of the Kraus operators is proved. The matrix representation for these solutions is obtained, which is incongruous with the result in the book completed by Nielsen and Chuang [Quan- tum Computation and Quantum Information, Cambridge University Press, 2000]. As especial cases, we also present the Kraus operator solutions to master equations for describing the amplitude-decay model and the diffusion process at finite temperature.
We study how can an angular momentum coherent state |τ> keeps its form-invariant during time evolution governed by the Hamiltonian H = f(t)J++ f^*(t)J-+ g(t)Jz. We discuss this topic in the context of boson realization of |τ>. By employing the entangled state representation |ζ> and deriving a new binomial theorem involving two-subscript Hermite polynomials, we derive the wave function <ζ|τ>, which turns out to be a single-subscript Hermite polynomial. Based on this result the maintenance of angular momentum coherent state during time evolution is examined, and the value of τ(t) is totally determined by the parameters involved in the Hamiltonian.
We theoretically introduce two new photon-modulated atomic coherent states(ACSs)via using the Schwinger bosonic representation of the angular momentum operators(the sequential operations J±n)on an ACS,and investigate their nonclassicality using the Wigner distribution,photon number distribution,and entanglement entropy.It is found that photonmodulated ACSs possess more stronger nonclassicality than the original ACS in certain regions ofτ,the nonclassicality enhances with increasing number n of the operations J±and the operation J+(-)n enhances the entanglement in the region of small(large)τ.
Two new photon-modulated spin coherent states(SCSs)are introduced by operating the spin ladder operators J±on the ordinary SCS in the Holstein-Primakoff realization and the nonclassicality is exhibited via their photon number distribution,second-order correlation function,photocount distribution and negativity of Wigner distribution.Analytical results show that the photocount distribution is a Bernoulli distribution and the Wigner functions are only associated with two-variable Hermite polynomials.Compared with the ordinary SCS,the photon-modulated SCSs exhibit more stronger nonclassicality in certain regions of the photon modulated number k and spin number j,which means that the nonclassicality can be enhanced by selecting suitable parameters.
