Approaching ultra-strong coupling in Transmon circuit-QED using a high-impedance resonator

  1. Sal J. Bosman,
  2. Mario F. Gely,
  3. Vibhor Singh,
  4. Daniel Bothner,
  5. Andres Castellanos-Gomez,
  6. and Gary A. Steele
In this experiment, we couple a superconducting Transmon qubit to a high-impedance 645 Ω 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 ultra-strong 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 ultra-strong coupling g¯∼0.45 with Transmon qubits.
arxiv pdf

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