Fig. 1: Experimental setup and scheme.
a The position of this work in a multiplexed quantum repeater protocol. This experiment represents part of the heralded entanglement generation in a long elementary link of a multiplexed quantum repeater. With two such remote atom-photon quantum correlations, together with the phase stability techniques, deployed fiber, and the synchronization of control systems demonstrated in recent works18,19,20,21,22,23,36, the heralded atom-atom entanglement over a metropolitan-scale elementary link can be established via single-photon interference in the future. b The protocol of this experiment. We use a full protocol in which the heralding signal arrives \(\frac{2L}{c}=120\,\mu {{\rm{s}}}\) after the excitation to simulate the real-world application. Here in this experiment, we implement the atom-photon quantum correlation between a quantum repeater node and a signal photon on one side in an elementary link, without the interference of the photons from both sides on the beamsplitter in the detection station for future atom-atom entanglement. To measure the quantum correlation of one side, the beamsplitter is not necessary. Thus, we can replace the beamsplitter and two detectors with one detector as depicted in b. In this protocol, pairs of quantum correlations between signal photon modes and corresponding memory (spin-wave) modes are generated successively. The signal modes are converted to C band and sent into a 12 km fiber one by one in time-bin pulses and detected after fiber transmission. The successful detection of a signal photon is converted to TTL pulse at the detector and is further sent back to the memory through another 12 km fiber with the help of two E/O (electric-optical) converters. The memory receives the heralding TTL pulse and reads out the corresponding memory mode according to the arrival time of the TTL pulse. The detection station and the memory are 5 m apart in a lab. The fibers are also in the same lab.
