Efficient algorithm for optimal control of mixed-state quantum systems

Zhu and Rabitz [J. Chem. Phys. 109, 385 (1998)] presented a rapidly convergent iterative algorithm for optimal control of the expectation value of a positive-definite observable in a pure-state quantum system. In this paper we generalize this algorithm to a quantum-statistical mechanics setting and show that it is both efficient in the mixed-state case and effective in achieving the control objective of maximizing the ensemble average of arbitrary observables in the cases studied.