We introduce a general but simple relation between the timescale for quantum coherence loss and the initial fluctuations of operators that couple a quantum system with a surrounding bath. The relation allows the prediction and measurement of early time decoherence dynamics for any open quantum system, through purity, without reconstructing the system’s many-body density matrix (see Fig. 1). Furthur, we have used this relation to develop a generalized theory for molecular electronic decoherence in the condensed phase. While usual models of electronic decoherence are based on pure dephasing ideas, it is shown formally and numerically that electronic transitions among diabatic states, and their interference with pure dephasing processes, also play a major role in the decoherence dynamics (Fig. 2). Such developments also offer a practical platform to test the ability of approximate quantum dynamics methods to capture decoherence. In particular, a class of mixed quantum-classical schemes for molecular dynamics where the bath is treated classically, such as Ehrenfest dynamics, are shown to correctly capture short-time decoherence when the initial conditions are sampled from the Wigner distribution. These advances offer new insights into how to mitigate the decoherence via initial state preparation, and provide a useful platform to develop decoherence times for molecular processes as well as to test approximate molecular dynamics methods.

Quantifying early time quantum decoherence dynamics through fluctuations

256th National Meeting (2018)

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