Fig. 6

Entropy change in a Carnot cycle. Change in entropy (in units of k_B) during stroke 2 of the modified Carnot cycle in Fig. 5 as a function of the stroke duration obtained by a numerical integration of the master equation. The upper (blue) curve corresponds to the reversibility criterion (7); it is seen that the inequality Σ ≥ 0 is far from being saturated. By contrast, our proposed inequality (11) is saturated (i.e., the equality sign applies) for sufficiently long stroke duration (red lower curve); here \(\Delta {\cal S}_{\mathrm{h}}(t) = {\cal S}\left( {\rho (t)} \right) - {\cal S}\left( {\rho _0} \right)\). Parameters: oscillator frequency ω(t) = (25 − 0.05κt)κ, k_BT_h = 5ħκ and squeezing parameter r = 0.2, κ being the decay rate of the cavity