Theoretical analysis is given of nonclassicality and decoherence of the fieldstates generated by adding any number of photons to the squeezed thermal state(STS). Based on the fact that the squeezed number state can be considered as asingle-variable Hermite polynomial excited state, the compact expression of thenormalization factor is derived, a Legendre polynomial. The nonclassicality isinvestigated by exploring the sub-Poissonian and negative Wigner function (WF).The results show that the WF of single photon-added STS (PASTS) always hasnegative values at the phase space center. The decoherence effect on PASTS isexamined by the analytical expression of WF. It is found that a longerthreshold value of decay time is included in single PASTS than in single-photonsubtraction STS.
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