Effective Markovian description of decoherence in bound systems

Abstract

Effective descriptions accounting for the evolution of quantum systems that are acted on by a bath are desirable. As the number of bath degrees of freedom increases and full quantum simulations turn out computationally prohibitive, simpler models become essential to understand and gain an insight into the main physical mechanisms involved in the system dynamics. In this regard, vibrational decoherence of an I$_2$ diatomics is tackled here within the framework of Markovian quantum state diffusion. The I$_2$ dynamics are analyzed in terms of an effective decoherence rate, $\Lambda$, and the specific choice of the initial state, in particular, Gaussian wave packets and two-state superpositions. It is found that, for Markovian baths, the relevant quantity regarding decoherence is the product of friction ($\eta$) and temperature ($T$); there is no distinction between varying one or the other. It is also observed that decoherence becomes faster as the energy levels involved in the system state correspond to higher eigenvalues. This effect is due to a population redistribution during the dynamical process and an eventual irreversible loss of the initial coherence. These results have been compared with those available in the literature from more detailed semiclassical IVR simulations, finding a good agreement.Comment: 12 pages, 9 figure

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“…To some extent, one might consider that the above results for Λ = 0 are counter intuitive. In principle, one would expect a gradual suppression of all terms outside the main diagonal of the real part of the density matrix [50,66,67,69]. However, although certainly the rich interference structure outside this diagonal disappears, certain traits related to the x − x exchange symmetry still persist.…”

“…Eventually this serves to better understand more refined and exact models, where such splitting is not possible due to their intrinsic formal and conceptual nature. Under Markovian conditions decoherence has important effects on both the position and the energy representations [50]. Thus, the model here considered relies on these observations and consists of a simple Markovian, coherence-damping term where energy differences between eigenstates and twopoint position correlations appear separately.…”

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