R. Chakrabarti, B. Virgin Jenisha
We study evolution of bipartite entangled quasi-Bell states in a qubit-oscillator system in the moderately strong coupling regime and also in the presence of a static bias. Using the adiabatic approximation that relies on the separation of the time scales of the two components, the reduced density matrices for the qubit and the oscillator degrees of freedom are obtained in closed forms comprising of linear combinations of Jacobi theta functions. The analytical results based on theta functions are found to be in good agreement with their series counterparts in the said parametric regime. The entropy of the system quantifying the entanglement is computed via the qubit reduced density matrix. The time dependence of this density matrix owes its origin to the bias term. The reduced density matrix of the oscillator is employed for obtaining the phase space distributions such as the Husimi Q-function,which, in turn, is utilized for extracting expectation values of antinormally ordered operators.
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http://arxiv.org/abs/1302.2771
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