Effects of the measurement power on states discrimination and dynamics in a circuit-QED experiment

TL;DR

This paper investigates how high photon numbers in a circuit-QED setup influence state discrimination, dynamics, and calibration, especially considering non-linear effects and state dressing in a superconducting weak link system.

Contribution

It demonstrates the impact of measurement power on state discrimination, transition rates, and calibration in a circuit-QED experiment involving Andreev states, extending analysis beyond the dispersive limit.

Findings

Non-linearity affects cavity frequency shifts and state discrimination.

Transition rates between states are power-dependent.

Theoretical modeling includes dressing of Andreev states by the cavity.

Abstract

We explore the effects of driving a cavity at a large photon number in a circuit-QED experiment where the ``matter-like'' part corresponds to an unique Andreev level in a superconducting weak link. The three many-body states of the weak link, corresponding to the occupation of the Andreev level by 0, 1 or 2 quasiparticles, lead to different cavity frequency shifts. We show how the non-linearity inherited by the cavity from its coupling to the weak link affects the state discrimination and the photon number calibration. Both effects require treating the evolution of the driven system beyond the dispersive limit. In addition, we observe how transition rates between the circuit states (quantum and parity jumps) are affected by the microwave power, and compare the measurements with a theory accounting for the ``dressing'' of the Andreev states by the cavity.