Guided motion in a dissipative quantum system: vibrational state preparation using picosecond infrared pulses Original Research Article

The influence of relaxation and dephasing on the selective excitation of vibration l states is studied within the framework of the density matrix.theory. As an example, the OH stretching vibration of water has been chosen. The potential energy surface (PES) can be well described by a Morse potential and the corresponding vibrational eigenstates are taken to expand the density matrix. If any coupling to the environment is neglected we can reproduce the results of other authors of a nearly 100% efficiency of excited state preparation. This is reached by since-squared shaped infrared laser pulses of about 1 ps duration. If the stretching vibration is coupled to a dissipative environment such a selectivity could not be achieved. Investigating the dependence of the state preparation on the pulse parameters one obtains that those pulses which where the optimal ones in the isolated molecule remain the best even in the presence of relaxation and dissipation. However, the efficiency of the state preparation may decrease remarkably below 100% if a coupling to the environment is present. This loss of the efficiency can be reduced by appropriate chosen spectral densities of the environmental degrees of freedom.