Photoselective adaptive femtosecond quantum control in the liquid phase

Coherent light sources can be used to manipulate the outcome of light–matter interactions by exploiting interference phenomena in the time and frequency domain. A powerful tool in this emerging field of ‘quantum control’1,2,3,4,5,6 is the adaptive shaping of femtosecond laser pulses7,8,9,10, resulting, for instance, in selective molecular excitation. The basis of this method is that the quantum system under investigation itself guides an automated search, via iteration loops, for coherent light fields best suited for achieving a control task designed by the experimenter11. The method is therefore ideal for the control of complex experiments7,12,13,14,15,16,17,18,19,20. To date, all demonstrations of this technique on molecular systems have focused on controlling the outcome of photo-induced reactions in identical molecules, and little attention has been paid to selectively controlling mixtures of different molecules. Here we report simultaneous but selective multi-photon excitation of two distinct electronically and structurally complex dye molecules in solution. Despite the failure of single parameter variations (wavelength, intensity, or linear chirp control), adaptive femtosecond pulse shaping can reveal complex laser fields to achieve chemically selective molecular excitation. Furthermore, our results prove that phase coherences of the solute molecule persist for more than 100 fs in the solvent environment.