Realizing scalable quantum interconnects necessitates the integration of solid-state quantum memories with foundry photonics processes. While prior photonic integration efforts have relied upon specialized, laboratory-scale fabrication techniques, this work demonstrates the monolithic integration of a quantum memory platform with low-loss foundry photonic circuits via back-end-of-line deposition. We deposited thin films of titanium dioxide (TiO2) doped with erbium (Er) onto silicon nitride nanophotonic waveguides and studied Er optical coherence at sub-Kelvin temperatures with photon echo techniques. We suppressed optical dephasing through ex-situ oxygen annealing and optimized measurement conditions, which yielded an optical coherence time of 64 μs (a 5 kHz homogeneous linewidth) and slow spectral diffusion of 27 kHz over 4 ms, results that are comparable to state-of-the-art erbium devices. Combined with second-long electron spin lifetimes and demonstrated electrical control of Er emission, our findings establish Er:TiO2 on foundry photonics as a manufacturable platform for ensemble and single-ion quantum memories.
@article{arxiv.2506.17557,
title = {Erbium Quantum Memory Platform with Long Optical Coherence via Back-End of Line Deposition on Foundry-Fabricated Photonics},
author = {Shobhit Gupta and Robert M. Pettit and Ananthesh Sundaresh and Vasileios Niaouris and Skylar Deckoff-Jones and Daniel P. Crowley and Lewis G. Carpenter and Alan M. Dibos and Manish Kumar Singh and Sean E. Sullivan},
journal= {arXiv preprint arXiv:2506.17557},
year = {2026}
}