Programmable cavity QED with a fiber-integrated atomic array

Linking quantum processors into a distributed network requires efficient interfaces that convert quantum information between matter and flying optical photons with high fidelity. Neutral atoms coupled to optical cavities represent a powerful platform for this task. While optical tweezer arrays provide scalable, site-resolved control of neutral atoms, combining them with high-cooperativity optical cavities has historically been challenging due to geometric conflicts between optical access for trapping and the small mode volumes required for strong atom-photon interactions. This paper demonstrates a hybrid architecture that unites a multi-site atomic tweezer array with a high-cooperativity fiber-integrated microcavity.

The experimental system integrates a one-dimensional optical tweezer array of twelve rubidium-87 atoms with a fiber Fabry-Pérot microcavity of length 85 micrometers. The cavity features a high finesse and a small mode waist, yielding a high single-atom cooperativity that places the system deep into the strong-coupling regime. Individual optical tweezers are generated using an acousto-optic deflector, allowing precise positioning of each atom along the cavity standing-wave axis with subwavelength resolution. Direct, single-shot fluorescence imaging of the full atomic array is achieved by passing counter-propagating imaging beams through the cavity mirror separation without clipping, enabling high-fidelity readout of trap occupation.

By translating individual atoms through the standing-wave cavity field, the authors continuously tune the local atom-photon coupling strength from the strong-coupling regime at field antinodes down to near-zero coupling at nodes. This precise positional control overcomes the limitations of fixed intracavity lattices. When multiple atoms are loaded into the array, the optical response exhibits collectively enhanced vacuum Rabi splittings that scale precisely according to the Tavis-Cummings model as the square root of the atom number. Furthermore, this cooperative coupling enables cavity-assisted, non-destructive atom-number readout by probing the system near specific collective polariton resonances.