Time-resolved qubit readout via nonlinear Josephson inductance

TL;DR

This paper introduces a novel dispersive qubit readout method that captures the time evolution of a flux qubit by leveraging nonlinear coupling to a high-frequency harmonic oscillator, enabling high-fidelity, low-backaction measurements.

Contribution

It generalizes dispersive readout to provide real-time qubit dynamics using nonlinear coupling and lock-in detection, with validated simulations demonstrating low backaction and high fidelity.

Findings

Effective real-time qubit observable measurement

Low backaction and high fidelity demonstrated

Successful simulation of coherent qubit oscillations

Abstract

We propose a generalisation of dispersive qubit readout which provides the time evolution of a flux qubit observable. Our proposal relies on the non-linear coupling of the qubit to a harmonic oscillator with high frequency, representing a dc-SQUID. Information about the qubit dynamics is obtained by recording the oscillator response to resonant driving and subsequent lock-in detection. The measurement process is simulated for the example of coherent qubit oscillations. This corroborates the underlying measurement relation and also reveals that the measurement scheme possesses low backaction and high fidelity.