Quantum State Sensitivity of an Autoresonant Superconducting Circuit

TL;DR

This paper explores how a superconducting circuit's autoresonant behavior is affected by quantum states, enabling high-fidelity, rapid qubit readout through threshold sensitivity.

Contribution

It demonstrates the quantum state dependence of autoresonance thresholds in a superconducting circuit, proposing a new method for qubit measurement.

Findings

Autoresonance threshold varies with qubit-oscillator detuning.

Threshold sensitivity enables high-fidelity qubit readout.

Readout speed is not limited by oscillator Q.

Abstract

When a frequency chirped excitation is applied to a classical high-Q nonlinear oscillator, its motion becomes dynamically synchronized to the drive and large oscillation amplitude is observed, provided the drive strength exceeds the critical threshold for autoresonance. We demonstrate that when such an oscillator is strongly coupled to a quantized superconducting qubit, both the effective nonlinearity and the threshold become a non-trivial function of the qubit-oscillator detuning. Moreover, the autoresonant threshold is sensitive to the quantum state of the qubit and may be used to realize a high fidelity, latching readout whose speed is not limited by the oscillator Q.