State-dependent impedance of a strongly coupled oscillator-qubit system

TL;DR

This paper explores how a resonant harmonic oscillator can be used as a quantum probe to measure two-state qubits at finite temperatures, revealing state-dependent impedance properties.

Contribution

It introduces a combined numerical and analytical approach to calculate system properties and demonstrates how impedance measurements can inform qubit state detection.

Findings

Impedance varies with qubit state.

Correlators encode information about the qubit.

Method enables finite-temperature qubit measurement.

Abstract

We investigate the measurements of two-state quantum systems (qubits) at finite temperatures using a resonant harmonic oscillator as a quantum probe. The reduced density matrix and oscillator correlators are calculated by a scheme combining numerical methods with an analytical perturbation theory. Correlators provide us information about the system impedance, which depends on the qubit state. We show in detail how this property can be exploited in the qubit measurement.