On-demand generation of indistinguishable polarization-entangled photon pairs

An on-demand source of indistinguishable and entangled photon pairs is a fundamental component of various quantum information applications, including optical quantum computing, quantum repeaters, quantum teleportation and quantum communication(1). Parametric downconversion(2,3) and four-wave mixing sources(4) of entangled photons have shown high degrees of entanglement and indistinguishability, but the probabilistic nature of their generation process also creates zero or multiple photon pairs following a Poissonian distribution. This limits their use in complex algorithms where many qubits and gate operations are required. Here, we simultaneously show ultrahigh purity (g((2))(0) < 0.004), high entanglement fidelity (0.81 +/- 0.02), high two-photon interference non-post selective visibilities (0.86 +/- 0.03 and 0.71 +/- 0.04) and on-demand generation (efficiency epsilon(pair) = 0.86 +/- 0.08) of polarization-entangled photon pairs from a single semiconductor quantum dot. Through a two-photon resonant excitation scheme, the biexciton population is deterministically prepared by a pi-pulse (epsilon(biexciton) = 0.98 +/- 0.07). Applied on a quantum dot showing no exciton fine-structure splitting, this results in the deterministic generation of indistinguishable entangled photon pairs.