Generation and Detection of Photon Number States on Demand

The widely discussed applications in quantum information and quantum cryptography require radiation sources capable of producing a fixed number of photons. This paper reviews the work performed in our laboratory to produce these fields on demand. Two different methods are discussed. The first is based on the one-atom maser or the micromaser operating under the conditions of the so-called trapping states. In this situation the micromaser stabilises to a photon number state. The second device uses a single ion in an optical cavity. The latter setup was recently realised in our laboratory.