Experimental demonstration of memory-enhanced quantum communication

TL;DR

This paper demonstrates a memory-enhanced quantum communication system using a solid-state spin memory, achieving a four-fold increase in secret key rate for quantum key distribution over direct transmission, advancing quantum networks.

Contribution

It presents the first experimental realization of a solid-state spin memory integrated with nanophotonics for quantum communication, enabling asynchronous Bell-state measurements and improved key rates.

Findings

Four-fold increase in secret key rate for MDI-QKD

Successful implementation of a solid-state spin memory in a nanophotonic resonator

Operation at megahertz clock rates

Abstract

The ability to communicate quantum information over long distances is of central importance in quantum science and engineering. For example, it enables secure quantum key distribution (QKD) relying on fundamental principles that prohibit the "cloning" of unknown quantum states. While QKD is being successfully deployed, its range is currently limited by photon losses and cannot be extended using straightforward measure-and-repeat strategies without compromising its unconditional security. Alternatively, quantum repeaters, which utilize intermediate quantum memory nodes and error correction techniques, can extend the range of quantum channels. However, their implementation remains an outstanding challenge, requiring a combination of efficient and high-fidelity quantum memories, gate operations, and measurements. Here we report the experimental realization of memory-enhanced quantum communication. We use a single solid-state spin memory integrated in a nanophotonic diamond resonator to implement asynchronous Bell-state measurements. This enables a four-fold increase in the secret key rate of measurement device independent (MDI)-QKD over the loss-equivalent direct-transmission method while operating megahertz clock rates. Our results represent a significant step towards practical quantum repeaters and large-scale quantum networks.