Coupling Rydberg atoms to a chip-based superconducting microwave resonator using a strong single-photon transition

Interfaces between Rydberg atoms and superconducting circuits are of interest for networking neutral-atom and superconducting qubits. In this setting, a telecom band photon could be used to address the state of the superconducting qubit in an interaction mediated by the atom. Experiments directed towards the development of such an interface have, up to now, involved coupling Rydberg atoms to a superconducting coplanar waveguide (CPW) resonator, using either two-photon transitions between Rydberg states in near-zero electric field [1], or single-photon transitions in strong DC offset fields applied to mitigate effects of stray electric fields from surface adsorbates [2]. In these situations, the effective electric dipole transition moments for single-photon absorption were ~50 and ~30 ea₀, respectively. Here, we demonstrate the coupling of a strong single-photon electric dipole transition between the 1s50s ³S₁ and 1s50p ³P_J Rydberg states in helium in near-zero DC field, to the 11.752 GHz second harmonic mode of a CPW resonator. An additional microwave dressing field was used to tune this transition into resonance with the resonator using the AC Stark effect [3]. The electric dipole transition moment of ~1500 ea₀ associated with this transition allowed an atom-resonator coupling strength of ~100 Hz to be achieved. An increase of ~2 orders of magnitude over previous work.

[1] A. A. Morgan et al. Phys. Rev. Lett. 124, 193604 (2020) 

[2] M. Kaiser et al. Phys. Rev. Research 4, 013207 (2022)

[3] L. L. Brown et al. Phys. Rev. A 110, 022615 (2024)