Efficient nuclear spin - photon entanglement with optical routing

Quantum networks and distributed quantum computers rely on entanglement generation between photons and long-lived quantum memories. For large-scale architectures, one of the most crucial parameters is the efficiency at which entanglement can be created and detected. Here, we maximize the efficiency for the detection of hybrid entanglement between a nuclear spin qubit in diamond with a photonic time-bin qubit. Our approach relies on an optimal implementation of the photonic qubit analyzer, for which we use a high-speed electro-optic deflector to direct photons deterministically along the optimal interferometer paths. This way, we completely eliminate all cases in which photons are randomly lost due to the propagation in the wrong interferometer path. In this first demonstration experiment, we use nitrogen-vacancy center in diamond, for which we immediately demonstrate the presence of the entanglement. An extension to other spin-photon entanglement systems is straightforward. Further, our scheme can be used in the framework of quantum repeater networks, including spectral and temporal multiplexing strategies. Our results thus pave the way for the future high-performance quantum networks.