Control of mixed-state quantum systems by a train of short pulses
D. Sugny1, A. Keller2, O. Atabek2, D. Daems3, C. M. Dion4, S. Guérin1, and H. R. Jauslin1
1Laboratoire de Physiqie de l'Université de
Bourgogne, UMR CNRS 5027, BP 47870, 21078 Dijon, France
2Laboratoire de Photophysique Moléculaire du CNRS,
Bâtiment 213, Campus d'Orsay, 91405 Orsay, France
3Center for Nonlinear Phenomena and Complex Systems,
Université Libre de Bruxelles, CP 231, 1050 Brussels, Belgium
4Department of Physics, Umeå University, SE-901
87 Umeå, Sweden
A density matrix approach is developed for the control of a mixed-state quantum system using a time-dependent external field. This leads to the definition of a target density matrix constructed in a reduced Hilbert space as a specific combination of the eigenvectors of a given observable through weighting factors related to the initial statistics of the system. A train of pulses is considered as a possible strategy to reach this target. An illustration is given by considering the laser control of molecular alignment and orientation in thermal equilibrium.
This article has been published in The Physical Review A 72, 032704 (2005) and may be found at http://publish.aps.org/abstract/PRA/v72/e032704.
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