Experimental demonstration of memory-enhanced quantum communication

• Published in: Nature (London) Vol. 580; no. 7801; pp. 60 - 64
• Main Authors: Bhaskar, M. K., Riedinger, R., Machielse, B., Levonian, D. S., Nguyen, C. T., Knall, E. N., Park, H., Englund, D., Lončar, M., Sukachev, D. D., Lukin, M. D.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.04.2020; Nature Publishing Group
• Subjects: 140/125; 142/126; 639/624/400/482; 639/766/483/3925; 639/766/483/481; Humanities and Social Sciences; Mathematical research; multidisciplinary; Quantum computing; Science; Science (multidisciplinary); United States
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/s41586-020-2103-5

The ability to communicate quantum information over long distances is of central importance in quantum science and engineering 1 . Although some applications of quantum communication such as secure quantum key distribution 2 , 3 are already being successfully deployed 4 – 7 , their range is currently limited by photon losses and cannot be extended using straightforward measure-and-repeat strategies without compromising unconditional security 8 . Alternatively, quantum repeaters 9 , which utilize intermediate quantum memory nodes and error correction techniques, can extend the range of quantum channels. However, their implementation remains an outstanding challenge 10 – 16 , requiring a combination of efficient and high-fidelity quantum memories, gate operations, and measurements. Here we use a single solid-state spin memory integrated in a nanophotonic diamond resonator 17 – 19 to implement asynchronous photonic Bell-state measurements, which are a key component of quantum repeaters. In a proof-of-principle experiment, we demonstrate high-fidelity operation that effectively enables quantum communication at a rate that surpasses the ideal loss-equivalent direct-transmission method while operating at megahertz clock speeds. These results represent a crucial step towards practical quantum repeaters and large-scale quantum networks 20 , 21 . A solid-state spin memory is used to demonstrate quantum repeater functionality, which has the potential to overcome photon losses involved in long-distance transmission of quantum information.