Abstract

The quantum nondemolition (QND) method for photon counting, recently developed at ENS [1,2], can be used for determining the photon number distribution of a light field by repeating the measurement of a large ensemble of realization of the same state. It can be turned into a method of full reconstruction of the quantum state of the field in the cavity by performing a simple translation of this field before measuring its photon number distribution. Translation of the field state in phase space is easily achieved by coupling the cavity for a short time with a classical source radiating a controlled classical field with well defined phase and amplitude. For each translation, the photon number measurement provides linear constrains on all elements of the density matrix of the prepared field. By repeating this procedure for a large number of different displacements one obtains a full experimental determination of the density operator representing the quantum state of the field prepared in the cavity.

© 2009 IEEE