Optical coherent quantum control of ultrafast protein electron transfer

The optical control of a biological system has been challenging, although the control of the energy transfer and isomerization reaction has been successfully demonstrated. Here, we report on our studies of ultrafast electron-transfer (ET) dynamics in a protein flavodoxin as a function of optical pump-pulse chirp. With a transform-limited excitation pulse in 25 femtoseconds, we observed the excited-state wave packet dynamics in ET reactions with a dephasing time within 1 ps. By modulating the phase of the excitation pulses, the ultrafast ET dynamics was found to change from 100 to 300 fs due to the different wave packets prepared by chirped pulses. We further found that the coherent control through the modulated wave packets can propagate into the subsequent back ET reactions resulting in the dynamics varying from 500 to 800 fs. This successful demonstration of coherent controlled ET reactions paves the way to control a variety of complex ET processes in chemical and biological systems.