Coherent control of an effective two-level system in a non-Markovian biomolecular environment

We investigate the quantum coherent dynamics of an externally driven effective two-level system (TLS) subjected to a slow Ohmic environment characteristic of biomolecular protein-solvent reservoirs in photosynthetic light-harvesting complexes. By means of the numerically exact quasi-adiabatic propagator path integral (QUAPI) method we are able to include non-Markovian features of the environment and show the dependence of the quantum coherence on the characteristic bath cut-off frequency omega(c) as well as on the driving frequency omega(1) and the field amplitude A. Our calculations extend from the weak-coupling regime to the incoherent strong-coupling regime. In the latter case, we find evidence for a resonant behaviour, beyond the expected behaviour, when the reorganization energy E-r coincides with the driving frequency. Moreover, we investigate how the coherent destruction of tunnelling within the TLS is influenced by the non-Markovian environment.