Coherent control of the isomerization of retinal in bacteriorhodopsin in the high intensity regime

Coherent control protocols provide a direct experimental determination of the relative importance of quantum interference or phase relationships of coupled states along a selected pathway. These effects are most readily observed in the high intensity regime where the field amplitude is sufficient to overcome decoherence effects. The coherent response of retinal photoisomerization in bacteriorhodopsin to the phase of the photoexcitation pulses was examined at fluences of 1015 – 2.5 × 1016 photons per square centimeter, comparable to or higher than the saturation excitation level of the S 0 − S 1 retinal electronic transition. At moderate excitation levels of ∼6 × 1015 photons/cm2 (