Cavity-based single-photon sources

We introduce the basic concepts and characteristic properties of single-photon emitters based on resonator effects in optical cavities, and provide a review of the most prominent implementations. First we discuss the elementary principles of cavity quantum electrodynamics, which determine how single quantum systems couple to the quantised field modes of optical resonators, and then show how to exploit these principles in order to generate single photons on demand. Furthermore, we elucidate how to study the properties of the photons, namely their singleness and their spectral characteristics. In particular, it is explained how to use a Hanbury-Brown and Twiss interferometer to determine whether the photons arrive one-by-one, and how to probe their mutual indistinguishability with two-photon interference experiments of the Hong-Ou-Mandel type. Finally, we present a classification scheme applicable to most cavity-based photon emitters realised to date. This scheme allows us to assess the pros and cons of the most significant approaches - in particular with regard to photonic quantum computing and quantum communication, which are among the most promising applications to date.