Memory-Assisted Metropolitan Scale Quantum Key Distribution

Eric Bersin | David Levonian | Aziza Suleymanzade | Madison Sutula  | Denis Sukachev | Ralf Reidinger | Mihir Bhaskar | Dirk Englund  | Mikhail Lukin | P. Ben Dixon

The past decade has seen tremendous progress towards the development of quantum networking, wherein quantum states are transmitted over long distances for applications in networked quantum computing, quantum key distribution, and quantum-enhanced metrology. In particular, recent results have demonstrated the fundamental building blocks of “quantum repeaters” – memories with photonic interfaces that can store and retransmit photonic qubits while in transit. Such repeaters are key to implementing scalable quantum networks, but thus far the work in this area has typically been confined to laboratory environments. Here, we demonstrate work towards performing memory-enhanced measurement-device-independent quantum key distribution (MDI QKD) over a deployed fiber link in the Boston metropolitan area. We select the diamond silicon vacancy (SiV) defect center as our quantum memory, due to its long spin coherence >10 ms at cryogenic temperatures and strong, stable optical transition. Working over a 50 km deployed fiber link, we demonstrate a low-noise frequency conversion to telecom band, as well as timing synchronization and frequency distribution schemes that are compatible with the memory’s operation to enable distribution and storage of qubits across our network testbed.

Funding Sources: NASA Space Technology Research Fellowship | MIT Lincoln Laboratory