Combined influence of random and regular external fields on long-range electron transfer

The dissipative dynamics of a two-level system (TLS) is studied for the case of the simultaneous modulation of the energy bias by a regular external field and by nonequilibrium dichotomic fluctuations. To describe the noise-averaged dynamics driven by the external periodic field, a set of coupled generalized master equations is derived. Quantum fluctuations of the thermal bath are taken into account within the noninteracting blip approximation, whereas the dichotomic fluctuations and the external field are treated in an exact manner. The case of nonadiabatic continuous-wave (cw) driving is considered in detail for an asymmetric TLS strongly coupled to the thermal bath. The general approach is applied to long-range electron transfer in proteins. According to the presence of dynamic disorder, the coarse-grained electron transfer dynamics becomes nonexponential. The gated regime and the inversion effect of the transfer in the strongly biased TLS with a dichotomic fluctuating energy bias are demonstrated. Additionally, it is shown that a strong cw field can switch the electron transfer dynamics between the gated (nonexponential) regime and the nonadiabatic (single-exponential) regime.