Generation of heralded entanglement between distant hole spins

Abstract

Quantum entanglement emerges naturally in interacting quantum systems and plays a central role in quantum information processing. But the generation of entanglement does not require direct interactions: single-photon detection in spin-flip Raman scattering projects two distant spins onto a maximally entangled state, provided that it is impossible to determine the source of the detected photon. Here, we demonstrate such heralded quantum entanglement of two quantum-dot hole spins separated by 5 m using single-photon interference. Thanks to fast spin initialization in 10 ns, hole-spin coherence lasting â 1/440 ns and efficient photon extraction from dots embedded in leaky microcavity structures, we generate 2,300 entangled spin pairs per second, which represents a 1,000-fold improvement as compared to previous experiments. The delayed two-photon interference scheme we developed allows the efficient verification of quantum correlations. Combined with schemes for transferring quantum information to a long-lived memory qubit, fast entanglement generation could impact quantum repeater architectures.