Strong coupling of a reconfigurable 171Yb atom array to a tunable telecom-band nanofiber cavity

Hideki Ozawa, Neville Chen, Yusuke Hisai, Shunichiro Hashimoto, Kenichi N. Komagata, Remi T. Oddon, Shanjou Yang, Seitaro Horikawa, Seigo Kikura, Shigehito Miki, Takao Aoki, Tadayuki Yoshitake, Hideki Konishi, Shinichi Sunami, Akihisa Goban, Ryotaro Inoue

Nanophotonic cavities provide strong atom-photon coupling in a compact, directly fiber-coupled geometry, while a reconfigurable array of 171Yb atoms combines high-fidelity gates with a metastable qubit state coupled directly to a telecom-band transition, making the two a natural interface between neutral-atom quantum processors and telecom quantum networks. Here, we realize strong atom-cavity coupling on the 3P0↔3D1 transition of 171Yb, establishing, to our knowledge, the first neutral-atom cavity-QED system to reach the single-atom strong-coupling regime on a telecom-band atomic transition. Reflection spectroscopy of a single-sided cavity yields a single-atom internal cooperativity of Cin=5.6(1.0) and collective coupling following √N scaling up to N=5 atoms, with homogeneous coupling at antinodes over ∼200 μm along the nanofiber. Thermal tuning of a fiber Bragg grating provides in situ control of the cavity outcoupling rate over two orders of magnitude from the undercoupled to the overcoupled regime, relevant for various atom-cavity protocols. We confirm compatibility with reconfigurable atom arrays by demonstrating 99.95(6) % imaging fidelity and trap lifetimes comparable to free-space array, at 1 μm from the nanofiber axis. Moreover, the diameter-engineered antireflection design of the nanofiber enables tweezer-based atom transport across the nanofiber with no measurable loss or heating at 4.5 μm above the nanofiber, supporting a two-layer architecture for the nanofiber-integrated atom array. From the demonstrated atom-cavity coupling, atom capacity, and cavity mode profile, we project time-multiplexed remote atom-atom entanglement generation at 40 kHz, with prospects for further scaling through technical enhancements and channel multiplexing.