ENTROPY OF A TWO LEVEL ATOM IN CONTACT WITH A SQUEEZED RESERVOIR

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Abstract
We study the entropy of a two level atom in contact with a non-minimum uncertainty squeezed reservoir and a coherent drive. Let δ be the phase of the coherent drive, and ΩR/γ the Rabi frequency divided by the atomic decay rate. For large, near minimum uncertainty squeezing, we find that the atomic quantum state is approximately a pure state, or, equivalently, a minimum entropy state, if ΩR/γ and δ satisfy (ΩR/γ)| cos δ| = 1/2. (Previous workers have only noted the occurrence of a pure state at δ = 0 or 180°.) We find that the atom saturates separately in each quadrature of the coherent drive. We also find that the thermodynamic order of the atom (given by the magnitude of the Bloch vector or by the negative of the atomic entropy) may increase as the background fluctuations or disorder increase. This behavior does not occur with non-squeezed reservoirs; it may be interpreted as a negative temperature effect, if atomic temperatures are defined in terms of the derivatives of the atomic entropy with respect to the variances of the two reservoir quadratures. We give an extensive collection of plots of the atomic entropy and temperatures. We find that a harmonic oscillator always cools down to lower temperatures than a 2 level atom if both bodies are in contact with the same squeezed reservoir.

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