Circuit Quantum Electrodynamics with Transmon Qubits in the Ultrastrong Coupling Regime

T. Niemczyk, Frank Deppe, Hans Huebl +9 more

Pierre Nataf, Cristiano Ciuti

Will Shanks, Devin Underwood, Andrew Houck

Sal J. Bosman, Mario F. Gely, Vibhor Singh +3 more

In this experiment, we couple a superconducting transmon qubit to a high-impedance $645\phantom{\rule{0.28em}{0ex}}\mathrm{\ensuremath{\Omega}}$ microwave resonator. Doing so leads to a large qubit-resonator coupling rate $g$, measured through a large vacuum Rabi splitting of $2g\ensuremath{\simeq}910$ MHz. The coupling is a significant fraction of the qubit and resonator oscillation frequencies $\ensuremath{\omega}$, placing our system close to the ultrastrong coupling regime ($\overline{g}=g/\ensuremath{\omega}=0.071$ on resonance). Combining this setup with a vacuum-gap transmon architecture shows the potential of reaching deep into the ultrastrong coupling $\overline{g}\ensuremath{\sim}0.45$ with transmon qubits.

Marios Kounalakis, Yaroslav M. Blanter, Gary Alexander Steele

The paper proposes a hybrid circuit for controlling a mechanical beam at the quantum level using a superconducting qubit. Using parameters obtained from recent experiments with similar devices, the authors show that the system can be tuned into a ultrastrong-coupling regime, where the interaction strength is comparable or even larger than the mechanical frequency.

Tian 甜 Tian 田, Xianhe 先和 Zhu 朱, Xi 茜 Tian 田

Abstract The circuit quantum electrodynamics (QED) system has brought us into an ultrastrong and deep coupling regime in the light–matter interaction community, in which the quantum effect has attracted significant interest. In this study, we theoretically investigated the photon blockade phenomenon in a double-transmon system operating in an ultrastrong coupling regime. We considered the effect of the counter-rotating wave terms in the interaction Hamiltonian and derived the master equation in the eigenpresentation. We found that photon blockade occurred in only one of the eigenmodes, and the counter-rotating wave terms enhanced the blockade by reducing the minimum value of the second-order correlation function. This study will be beneficial for the design of single-photon devices in circuit QED systems, especially in the ultrastrong coupling regime.