We propose a technique to probe the quantum state of light in an optical cavity without significantly altering it. We minimize the interaction of the probe with the field by arranging a setting where the largest contribution to the transition probability is canceled. We show that we obtain a very good resolution to measure photon population differences between two given Fock states by means of atomic interferometry.

• Received 10 September 2013

DOI:https://doi.org/10.1103/PhysRevA.88.063824