Thermal effects on coherence and excitation transfer. (arXiv:1708.03382v2 [quant-ph] UPDATED)

To control and utilize quantum features in small scale for practical
applications such as quantum transport, it is crucial to gain deep
understanding of quantum characteristics of states such as coherence. Here by
introducing a technique that simplifies solving the dynamical equation, we
study the dynamics of coherence in a system of qubits interacting with each
other through a common bath at non zero temperature. Our results demonstrate
that depending on initial state, environment temperature affect coherence and
excitation transfer in different ways. We show that when initial state is
incoherent, as time goes on, coherence and probability of excitation transfer
increase. But for coherent initial state, we find a critical value of
temperature, below which system loses its coherence in time which diminishes
the probability of excitation transfer. Hence in order to achieve higher value
of coherence and also higher probability of excitation transfer, temperature of
the bath should go beyond that critical value. Stationary coherence and
probability of finding excited qubits in steady state, are discussed. We also
elaborate on dependence of critical value of bath temperature on system size.

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