Enhanced state control and tunability at a Rydberg-atom superconducting circuit interface

Rydberg atoms are well suited to interfacing with superconducting microwave circuits for applications in hybrid quantum information processing. This is because of their large electric dipole transition moments at microwave frequencies, and long coherence times. Recently, helium Rydberg atoms were coupled to the 19.556 GHz mode of a niobium nitride coplanar waveguide resonator [1-3]. This resonator field drove the two photon 55s-56s transition between triplet Rydberg states. As will be presented in this talk, to extend this work, with the goal of accessing the single-photon strong-coupling regime of this hybrid cavity QED system, two additional nonresonant microwave fields have been incorporated into the experiment. These fields (1) null the polarizability of the 55s-56s transition so that the atoms can be located closer to the surface of the cryogenically cooled superconducting chip where the microwave field is stronger without detrimental effects from stray electric fields, and (2) allow the implementation of two-color microwave transitions to enhance the coupling strength of the atoms to the resonator. The resulting engineered helium Rydberg atom qubit is particularly well suited to applications in quantum technologies, including, e.g., microwave to optical photon conversion.

[1] A. A. Morgan and S. D. Hogan Phys. Rev. Lett. 124, 193604 (2020)

[2] D. M. Walker, A. A. Morgan, and S. D. Hogan Appl. Phys. Lett. 117, 204001 (2020)

[3] D. M. Walker, L. L. Brown, and S. D. Hogan Phys. Rev. A 105, 022626 (2022)