  The Rabi Hamiltonian describes the interaction between a two-level atom and a
single mode of the quantized electromagnetic field. When the system is subject
to the Markovian atomic dephasing reservoir, the anti-rotating term leads to
the photon generation from vacuum. In the presence of Markovian damping
reservoirs, the asymptotic mean photon number is higher than the thermal photon
number expected in the absence of the anti-rotating term. We obtain approximate
analytical expressions in the asymptotic regime for the photon creation rate in
the pure dephasing case and the mean photon number and the atomic population
inversion in the general case. Our analytical results are valid in the small
mean photon number limit and they were tested by numerical analyses.
