Nonlinear resonant behavior of the dispersive readout scheme for a superconducting flux qubit

TL;DR

This paper investigates the nonlinear resonant behavior of a superconducting flux qubit readout circuit, highlighting how nonlinearity and hysteresis depend on input power, supported by numerical simulations.

Contribution

It introduces a detailed analysis of nonlinearity and hysteresis in a SQUID-based dispersive readout scheme for flux qubits, supported by phenomenological circuit modeling.

Findings

Nonlinear resonance exhibits hysteresis depending on input power.

Numerical simulations replicate observed nonlinear features.

Resonance frequency shifts with flux state changes.

Abstract

A nonlinear resonant circuit comprising a SQUID magnetometer and a parallel capacitor is studied as a readout scheme for a persistent-current (PC) qubit. The flux state of the qubit is detected as a change in the Josephson inductance of the SQUID magnetometer, which in turn mediates a shift in the resonance frequency of the readout circuit. The nonlinearity and resulting hysteresis in the resonant behavior are characterized as a function of the power of both the input drive and the associated resonance peak response. Numerical simulations based on a phenomenological circuit model are presented which display the features of the observed nonlinearity.