  The nonclassicality of photon-added coherent fields in the thermal channel is
investigated by exploring the volume of the negative part of the Wigner
function which reduces with the dissipative time. The Wigner functions become
positive when the decay time exceeds a threshold value. For the case of the
single photon-added coherent state, we derive the exact threshold values of
decay time in the thermal channel. For arbitrary partial negative Wigner
distribution function, a generic analytical relation between the mean photon
number of heat bath and the threshold value of decay time is presented.
Finally, the possible application of SPACSs in quantum computation has been
briefly discussed.
  OCIS codes: 270.0270, 270.2500, 000.5490
