A variational master equation approach to dissipative energy transfer dynamics |
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| Ahsan Nazir | |
| Imperial College London | |
| Recent experiments demonstrating signatures of quantum coherence in the energy transfer dynamics of a variety of light-harvesting systems [1] have sparked renewed interest in the theoretical modelling of energy transfer processes. A major challenge remains the development of techniques which allow one to probe the diverse parameter regimes relevant to such systems. Master equation methods provide useful tools with which to efficiently analyse energy transfer dynamics in the presence of an external environment. However, they are often valid only in rather restrictive parameter regimes, limiting their applicability in the present context.
Here, I shall present a versatile variational master equation approach to the non-equilibrium dynamics of dissipative quantum systems, that allows for the exploration of a wide range of parameter regimes within a single formalism. Derived through the combination of a variationally-optimised unitary transformation [2] and the time-local projection operator technique, the master equation can be applied to a range of bath spectral densities, and accounts for both non-Markovian and non-equilibrium environmental effects. Applying the formalism in the case of excitation energy transfer, I shall show that while it correctly reproduces Redfield [3], polaron [4], and Foerster [5] dynamics in the appropriate limits, it can also be used in intermediate regimes where none of these theories may be applicable. I shall also discuss applications in a slightly different context, that of laser-driven semiconductor quantum dots [6]. Variational master equations thus represent a promising avenue for the exploration of dissipative dynamics in a variety of physical systems. [1] See, for example, H. Lee, Y.-C. Cheng, and G. R. Fleming, Science 316, 1462 (2007); G. S. Engel et al., Nature 446, 782 (2007); E. Collini and G. D. Scholes, Science 323, 369 (2009); E. Collini et al. Nature 463, 644 (2010); G. Panitchayangkoon et al., Proc. Natl. Acad. Sci. 107, 12766 (2010) |