Qubit state detection using the quantum Duffing oscillator

TL;DR

This paper proposes a qubit detection method using a driven nonlinear resonator exhibiting sharp few-photon resonances, enabling high-fidelity, low-back-action measurements by exploiting frequency shifts dependent on the qubit state.

Contribution

It introduces a novel detection scheme based on resonant few-photon transitions in a nonlinear resonator coupled to a qubit, enhancing read-out fidelity and efficiency.

Findings

The detection scheme achieves high discrimination power.

It offers small back action on the qubit.

The method demonstrates large measurement efficiency.

Abstract

We introduce a detection scheme for the state of a qubit, which is based on resonant few-photon transitions in a driven nonlinear resonator. The latter is parametrically coupled to the qubit and is used as its detector. Close to the fundamental resonator frequency, the nonlinear resonator shows sharp resonant few-photon transitions. Depending on the qubit state, these few-photon resonances are shifted to different driving frequencies. We show that this detection scheme offers the advantage of small back action, a large discrimination power with an enhanced read-out fidelity, and a sufficiently large measurement efficiency. A realization of this scheme in the form of a persistent current qubit inductively coupled to a driven SQUID detector in its nonlinear regime is discussed.