Diamond tin-vacancy (SnV) centers are promising candidates for building quantum network nodes. However, their native photon emission at 619 nm is incompatible with metropolitan-scale networks operating at low-loss telecom wavelengths. To address this, we demonstrate highly efficient, low-noise quantum frequency conversion (QFC) of 619 nm photons to the telecom S-band at 1480 nm. The conversion process combines 619 nm photons with 1064 nm pump light in an actively stabilized cavity containing a bulk monocrystalline potassium titanyl arsenate (KTA) crystal. We achieve an internal (external) conversion efficiency of (48 +/- 3)% ((28 +/- 2)%) and a noise photon rate per wavelength of 2.2 +/- 0.9 cts/s/pm, which is spectrally flat in the investigated frequency range of 40 GHz. Furthermore, we demonstrate that the efficiency remains above 80% of its maximum over a frequency range of 70 GHz. Finally, we generate a string of photons from a single waveguide-embedded SnV center using a train of excitation pulses and send these through the QFC. After the QFC, we observe a string of telecom photons displaying the SnV lifetime, confirming successful conversion. These results represent a critical step towards metropolitan-scale fiber-based quantum networks using SnV centers.
@article{arxiv.2509.01661,
title = {Quantum Frequency Conversion of Single Photons from a Tin-Vacancy Center in Diamond},
author = {Julia M. Brevoord and Jan Fabian Geus and Tim Turan and Miguel Guerrero Romero and Daniel Bedialauneta Rodríguez and Nina Codreanu and Alexander M. Stramma and Ronald Hanson and Florian Elsen and Bernd Jungbluth},
journal= {arXiv preprint arXiv:2509.01661},
year = {2025}
}