Quantum state engineering of light with continuous-wave optical   parametric oscillators
  The ability to engineer the quantum state of traveling optical fields is a central requirement for quantum information science and technology, including quantum communication, computing and metrology. In this video article, we describe the reliable generation of non-Gaussian states, including single-photon states and coherent state superpositions, using a conditional preparation method operated on the non-classical light emitted by optical parametric oscillators. Type-I and type-II phase-matched OPOs operated below threshold, i.e. single-mode or two-mode squeezed vacuum sources, are considered and common procedures, such as the required frequency filtering or the high-efficiency quantum state characterization by homodyning, are detailed. The reported method enables a high fidelity with the targeted state and the generation of the state in a well-controlled spatiotemporal mode, a crucial feature for their use in subsequent protocols. 
Olivier Morin, Jianli Liu, Kun Huang, Felippe A. S. Barbosa, Claude   Fabre, Julien Laurat
quant-ph