Approaching ultrastrong coupling in transmon circuit QED using a high-impedance resonator
S.J. Bosman (TU Delft - QN/Steele Lab)
M.F. Gely (TU Delft - QN/Steele Lab)
Vibhor Singh (Indian Institute of Science)
Daniel Bothner (TU Delft - QN/Steele Lab)
Andres Castellanos-Gomez (Instituto de Ciencia de Materiales de Madrid (ICMM))
GA Steele (TU Delft - QN/Steele Lab)
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Abstract
In this experiment, we couple a superconducting transmon qubit to a high-impedance 645Ω microwave resonator. Doing so leads to a large qubit-resonator coupling rate g, measured through a large vacuum Rabi splitting of 2g≃910 MHz. The coupling is a significant fraction of the qubit and resonator oscillation frequencies ω, placing our system close to the ultrastrong coupling regime (g=g/ω=0.071 on resonance). Combining this setup with a vacuum-gap transmon architecture shows the potential of reaching deep into the ultrastrong coupling g∼0.45 with transmon qubits.