Measuring the density matrix by local addressing - art. no. 065401

We introduce a procedure to measure the density matrix of a material system . The density matrix is addressed locally in this scheme by applying a sequ ence of delayed-light pulses. The procedure is based on the stimulated Rama n adiabatic passage technique. It is shown that a series of population meas urements on the target state of the population transfer process yields unam biguous information about the populations and coherences of the addressed s tates, which, therefore, can be determined.