Realization of a cavity-coupled Rydberg array

Scalable quantum computers and quantum networks require the combination of quantum processing nodes with efficient light-matter interfaces to distribute quantum information in local or long-distance quantum networks. Neutral-atom arrays have both been coupled to Rydberg states to enable high-fidelity quantum gates in universal processing architectures, and to optical cavities to realize interfaces to photons. However, combining these two capabilities and coupling atom arrays to highly excited Rydberg states in the mode of an optical cavity has been an outstanding challenge. Here we present a novel cavity-coupled Rydberg array that achieves this long-standing goal. We prepare, detect, and control individual atoms in a scalable optical tweezer array, couple them strongly to the optical mode of a high-finesse optical cavity and excite them in a controlled way to Rydberg states. We show that strong coupling to an optical cavity - demonstrated via the dispersive shift of the resonance of the cavity in presence of the atoms - and strong Rydberg interactions - demonstrated via the collective enhancement of Rydberg coupling in the atomic array - can be achieved in our setup at the same spatial location. Our presented experimental platform opens the path to several new directions, including the realization of quantum network nodes, quantum simulation of long-range interacting, open quantum systems and photonic-state engineering leveraging high-fidelity Rydberg control.

💡 Research Summary

In this work the authors present a fully integrated experimental platform that brings together three essential ingredients for scalable quantum information processing: (i) a programmable tweezer array of neutral 87Rb atoms, (ii) a high‑finesse near‑concentric optical cavity operating in the strong‑coupling regime of cavity QED, and (iii) coherent excitation of the atoms to a high‑lying Rydberg state within the cavity mode. The tweezer array is generated with a spatial light modulator at 1015 nm, allowing arbitrary geometries of up to 49 traps. Individual atoms are loaded with a 52 % probability, imaged with 99.988 % fidelity, and survive with 99.88 % probability over long interrogation times, establishing a reliable qubit register.

The cavity consists of two 10 mm radius‑of‑curvature mirrors spaced by ~20 mm, giving a free‑spectral range of 7.79 GHz and a linewidth κ = 2π × 0.84 MHz. The mode profile is essentially Gaussian, but the authors observe a splitting of the resonance into several sub‑modes spaced by ~3 MHz, which they attribute to hybridisation of higher‑order transverse modes caused by non‑paraxial effects and mirror imperfections. Accounting for these hybrid modes, the measured cooperativity reaches C ≈ 1, confirming that the system operates in the single‑atom strong‑coupling regime.

To verify atom‑cavity coupling, a 7 × 7 stochastic loading of the array is used. With the cavity detuned 73 MHz from the atomic cycling transition, the authors measure a dispersive shift of the cavity resonance proportional to the atom number. For an average of ⟨N⟩ ≈ 23.3 atoms they find a total shift of 2π × 206 kHz, corresponding to a single‑atom shift of 2π × 9 kHz and an inferred single‑atom cooperativity of C ≈ 0.5. After correcting for the spatial variation of the standing‑wave field, the true cooperativity is consistent with the cavity‑only estimate of C ≈ 1.

A major technical hurdle is the electric field generated by the piezo actuators used to stabilize the cavity length, which can Stark‑shift Rydberg levels. The authors embed the piezos in a titanium platform that acts as an electrostatic shield. Finite‑element simulations and direct spectroscopy of the 53S₁/₂ Rydberg state show that the Stark shift is reduced by more than an order of magnitude compared with an unshielded configuration, effectively suppressing the field at the atom position to the few mV/cm level. Consequently, the two‑photon Rydberg excitation (420 nm + 1015 nm, intermediate detuning Δ = 2π × 2 GHz) remains narrow and well‑controlled inside the cavity.

Rydberg blockade is demonstrated by preparing small, well‑defined sub‑arrays (2 × 2, 3 × 3, 4 × 4) within the cavity mode and driving the collective Rydberg transition. The measured Rabi frequency scales as Ω ∝ √N, confirming the formation of symmetric W‑type entangled states and the presence of strong van‑der‑Waals interactions despite the proximity of dielectric mirrors. This result shows that the cavity does not degrade the blockade radius and that coherent many‑body dynamics can be explored in a cavity‑QED environment.

Overall, the paper delivers a versatile platform that merges high‑fidelity atom‑by‑atom control, strong atom‑photon coupling, and robust Rydberg excitation. The authors discuss several promising directions: (1) quantum network nodes where the cavity mediates photon emission and retrieval while the Rydberg interaction provides deterministic entanglement between stored qubits; (2) simulation of open quantum systems with long‑range interactions, exploiting the combination of cavity‑mediated dissipation and Rydberg‑induced Hamiltonians; (3) generation of non‑classical photonic states via Rydberg‑enhanced nonlinearities inside the cavity; and (4) scaling to larger arrays for fault‑tolerant quantum computing architectures that require both fast two‑qubit gates (Rydberg) and efficient light‑matter interfaces (cavity). The work thus represents a significant step toward integrated neutral‑atom quantum processors that can be directly linked into photonic quantum networks.