Spontaneous parametric down conversion has served as an excellent workhorse for fundamental test of quantum mechanics, proof-of-principle demonstrations of multi-photon entanglement [1], quantum teleportation [2] and optical quantum computing [3]. Yet, its probabilistic nature and higher-­â€order photon emission limit the scalability in optical quantum information processing. Self-­â€assembled quantum dots (QD) are deterministic single-photon emitters on a solid-state platform with high quantum efficiency and light-matter interface. For quantum information applications, the three most important metrics are the photon purity, indistinguishability, and efficiency. These key properties have been compatibly combined simultaneously on the same QD-micropillar very recently [4,5]. An important next challenge is to extend the single-photon sources to multiple photonic qubits. To this end, by pulsed s-­â€shell resonant excitation of a single QD-micropillar, we generate long streams of thousands of single photons with high mutual indistinguishability [6], which allowed scalable multi-photon Boson sampling experiments with a performance beating the best parametric down-conversion sources.

References: [1] J.-W. Pan et al. Rev. Mod. Phys 84, 777 (2012). [2] X.L. Wang et al. Nature 518, 516 (2015). [3] X.D. Cai et al. Phys. Rev. Lett. 114, 110504 (2015). [4] Y.M. He et al. Nature Nanotechnology 8, 213 (2013); [5] X. Ding et al. Phys. Rev. Lett. 116, 020401 (2016); N. Somaschi et al., arXiv:1510.06499 [6] H. Wang et al. in preparation (2016).