Laser pulse control of exciton dynamics in the FMO complex:: Polarization shaping versus effects of structural and energetic disorder

Femtosecond laser pulse control of exciton dynamics in biological chromophore complexes is studied theoretically using the optimal control theory specified to open quantum systems. Based on the laser pulse induced formation of an excitonic wave packet the possibility to localize excitation energy at a certain chromophore within a photosynthetic antenna system (FMO complex of green bacteria) is investigated both for linearly polarized and polarization shaped pulses. Results are presented for an ensemble of N energetically disordered and randomly oriented FMO complexes. Here, the optimized control pulse represents a compromise with respect to the solution of the control task for any individual complex of the ensemble. For the case of an ensemble with N = 10 members the polarization shaped control pulse leads to a higher control yield compared with a linearly polarized pulse. This difference becomes considerably smaller for an ensemble with N = 120 members. The respective optimized pulses are used to drive excitation energy in a different ensemble with M >> N complexes to simulate the usual experimental condition in solution. For the case with N = 120, the relative control yield coincides with the resulting control yield "in solution", giving a slightly higher control yield for polarization shaped pulses. (c) 2006 Elsevier B.V. All rights reserved.