Parametric longitudinal coupling of a semiconductor charge qubit and a RF resonator

TL;DR

This paper experimentally characterizes parametric longitudinal coupling between a CMOS charge qubit and an RF resonator, demonstrating controllable charge-photon interactions and their potential for scalable quantum architectures.

Contribution

It provides the first detailed experimental analysis of parametric longitudinal coupling in CMOS charge qubits, confirming theoretical models without fitting parameters.

Findings

Charge-photon couplings match theoretical formulas

Resonator state displacement depends on qubit state

Longitudinal coupling is insensitive to photon number

Abstract

In this study, we provide a full experimental characterization of the parametric longitudinal coupling between a CMOS charge qubit and an off-chip RF resonator. Following Corrigan et al, Phys. Rev. Applied 20, 064005 (2023), we activate parametric longitudinal coupling by driving the charge qubit at the resonator frequency. Managing the crosstalk between the drive applied to the qubit and the resonator allows for the systematic study of the dependence of the longitudinal and dispersive charge-photon couplings on the qubit-resonator detuning and the applied drive. Our experimental estimations of the charge-photon couplings are perfectly reproduced by theoretical simple formulas, without relying on any fitting parameter. We go further by showing a parametric displacement of the resonator's steady state, conditional on the qubit state, and the insensitivity of the longitudinal coupling constant on the photon population of the resonator. Our results open to the exploration of the photon-mediated longitudinal readout and coupling of multiple and distant spins, with long coherent times, in hybrid CMOS cQED architectures.