Quantum-memory-assisted multi-photon generation for efficient quantum information processing

Efficient preparation of large, but definite, numbers of photons is of great importance for scaling up and speeding up photonic quantum information processing. Typical single-photon generation techniques based on nonlinear parametric processes face challenges of probabilistic generation. Here we demonstrate efficient synchronization of photons from multiple nonlinear parametric heralded single-photon sources, using quantum memories. Our low-loss optical memories greatly enhance (∼30×) the generation rate of coincidence photons from two independent sources, while maintaining high indistinguishability (95.7±1.4%) of the synchronized photons. As an application, we perform the first demonstration of parametric-source-based measurement-device-independent quantum key distribution. The synchronization technique demonstrated here paves the way toward efficient quantum communication and larger-scale optical quantum computing.