Qubit measurement using a quantum point contact with a quantum Langevin equation approach

TL;DR

This paper develops a quantum Langevin equation framework to analyze non-Markovian dynamics and noise spectra in quantum dot qubit measurements via a quantum point contact, clarifying the origin of quantum oscillation peaks.

Contribution

It introduces a microscopic, non-Markovian approach to qubit measurement dynamics and noise analysis, resolving debates on quantum oscillation features in the spectrum.

Findings

Derived Bloch equations for qubit relaxation and decoherence.

Analyzed noise spectrum at various bias-voltage and temperature conditions.

Resolved the debate on quantum oscillation peaks in the measurement noise spectrum.

Abstract

We employ a quantum Langevin equation approach to establish non-Markovian dynamical equations, on a fully microscopic basis, to investigate the measurement of the state of a coupled quantum dot qubit by a nearby quantum point contact. The ensuing Bloch equations allow us to examine qubit relaxation and decoherence induced by measurement, and also the noise spectrum of meter output current with the help of a quantum regression theorem, at arbitrary bias-voltage and temperature. Our analyses provide a clear resolution of a recent debate concerning the occurrence of a quantum oscillation peak in the noise spectrum.