Floquet Study of Quantum Control of the Cis-Trans Photoisomerization of Rhodopsin

Understanding how to control reaction dynamics of polyatomic systems by using ultrafast laser technology is a fundamental challenge of great technological interest. Here, we report a Floquet theoretical study of the effect of light-induced potentials on the ultrafast cis trans photoisomerization dynamics of rhodopsin. The Floquet Hamiltonian involves an empirical 3-state 25-mode model with frequencies and excited state gradients parametrized to reproduce the rhodopsin electronic vertical excitation energy, the resonance Raman spectrum, and the photoisomerization time and efficiency as probed by ultrafast spectroscopy. We simulate the excited state relaxation dynamics using the time-dependent self-consistent field method, as described by a 3-state 2-mode nuclear wavepacket coupled to a Gaussian ansatz of 23 vibronic modes. We analyze the reaction time and product yield obtained with pulses of various widths and intensity profiles, defining 'dressed states' where the perturbational effect of the pulses is naturally decoupled along the different reaction channels. We find pulses that delay the excited-state photoisomerization for hundreds of femtoseconds, and we gain insights on the underlying control mechanisms. The reported findings provide understanding of quantum control, particularly valuable for the development of ultrafast optical switches based on visual pigments.