Quantum control of population transfer in green fluorescent protein by using chirped femtosecond pulses

We demonstrate that the methods of quantum control can be applied successfu lly to very large molecules in room temperature liquid solution. Chirped fe mtosecond pulses are used to excite a green fluorescent protein mutant in b oth buffered aqueous solution and solid acrylamide gel. At high energy dens ities, the fluorescence shows a strong chirp dependence, with positively ch irped pulses transferring almost 50% more population to the excited state t han negatively chirped pulses. By measuring the photobleaching rate in the gel as a function of pulse chirp, we find that the data are consistent with the bleaching of the protein being due to a thermal mechanism rather than to an excited-state photoreaction.