Quantum feedback by discrete quantum nondemolition measurements: Towards on-demand generation of photon-number states

We propose a quantum feedback scheme for the preparation and protection of photon-number states of light trapped in a high- Q microwave cavity. A quantum nondemolition measurement of the cavity field provides information on the photon-number distribution. The feedback loop is closed by injecting into the cavity a coherent pulse adjusted to increase the probability of the target photon number. The efficiency and reliability of the closed-loop state stabilization is assessed by quantum Monte Carlo simulations. We show that, in realistic experimental conditions, the Fock states are efficiently produced and protected against decoherence.