A quantum tale of different, yet inseparable photons

Quantum communication, the art of transferring quantum bits at a distance, requires reliable sources of entangled photons. We report on our efforts to create entangled photon pairs at widely separated wavelengths through three-wave mixing (parametric downconversion) in bulk PPLN crystals and four-wave mixing in microstructured fibre. As a benefit, we show how this approach also provided us with a high-quality source of single photon and we report on a fast and simple method we developed to characterize the desired suppression of multiphotons events.