Entanglement of nanophotonic quantum memory nodes in a telecom network

C M Knaut; A Suleymanzade; Y-C Wei; D R Assumpcao; P-J Stas; Y Q Huan; B Machielse; E N Knall; M Sutula; G Baranes; N Sinclair; C De-Eknamkul; D S Levonian; M K Bhaskar; H Park; M Lončar; M D Lukin

doi:10.1038/s41586-024-07252-z

Entanglement of nanophotonic quantum memory nodes in a telecom network

Nature. 2024 May;629(8012):573-578. doi: 10.1038/s41586-024-07252-z. Epub 2024 May 15.

Authors

C M Knaut^#¹, A Suleymanzade^#¹, Y-C Wei^#¹, D R Assumpcao^#², P-J Stas^#¹, Y Q Huan¹, B Machielse^{1

3}, E N Knall², M Sutula¹, G Baranes^{1

4}, N Sinclair², C De-Eknamkul³, D S Levonian^{1

3}, M K Bhaskar^{1

3}, H Park^{1

5}, M Lončar², M D Lukin⁶

Affiliations

¹ Department of Physics, Harvard University, Cambridge, MA, USA.
² John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA.
³ AWS Center for Quantum Networking, Boston, MA, USA.
⁴ Department of Physics and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA, USA.
⁵ Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA.
⁶ Department of Physics, Harvard University, Cambridge, MA, USA. lukin@physics.harvard.edu.

^# Contributed equally.

Abstract

A key challenge in realizing practical quantum networks for long-distance quantum communication involves robust entanglement between quantum memory nodes connected by fibre optical infrastructure^1-3. Here we demonstrate a two-node quantum network composed of multi-qubit registers based on silicon-vacancy (SiV) centres in nanophotonic diamond cavities integrated with a telecommunication fibre network. Remote entanglement is generated by the cavity-enhanced interactions between the electron spin qubits of the SiVs and optical photons. Serial, heralded spin-photon entangling gate operations with time-bin qubits are used for robust entanglement of separated nodes. Long-lived nuclear spin qubits are used to provide second-long entanglement storage and integrated error detection. By integrating efficient bidirectional quantum frequency conversion of photonic communication qubits to telecommunication frequencies (1,350 nm), we demonstrate the entanglement of two nuclear spin memories through 40 km spools of low-loss fibre and a 35-km long fibre loop deployed in the Boston area urban environment, representing an enabling step towards practical quantum repeaters and large-scale quantum networks.