Long-distance quantum communication and networking require quantum memory nodes with efficient optical interfaces and long memory times. We report the realization of an integrated two-qubit network node based on silicon-vacancy centers (SiVs) in diamond nanophotonic cavities. Our qubit register consists of the SiV electron spin acting as a communication qubit and the strongly coupled 29Si nuclear spin acting as a memory qubit with a quantum memory time exceeding two seconds. By using a highly strained SiV with suppressed electron spin-phonon interactions, we realize electron-photon entangling gates at elevated temperatures up to 1.5 K and nucleus-photon entangling gates up to 4.3 K. Finally, we demonstrate efficient error detection in nuclear spin-photon gates by using the electron spin as a flag qubit, making this platform a promising candidate for scalable quantum repeaters.
@article{arxiv.2207.13128,
title = {Robust multi-qubit quantum network node with integrated error detection},
author = {Pieter-Jan Stas and Yan Qi Huan and Bartholomeus Machielse and Erik N. Knall and Aziza Suleymanzade and Benjamin Pingault and Madison Sutula and Sophie W. Ding and Can M. Knaut and Daniel R. Assumpcao and Yan-Cheng Wei and Mihir K. Bhaskar and Ralf Riedinger and Denis D. Sukachev and Hongkun Park and Marko Lončar and David S. Levonian and Mikhail D. Lukin},
journal= {arXiv preprint arXiv:2207.13128},
year = {2022}
}