Continuous quantum measurement with independent detector cross-correlations

TL;DR

This paper explores how using two independent linear detectors in continuous quantum measurement can enhance measurement efficiency and surpass traditional bounds through cross-correlations, providing insights into ideal detector behavior and non-commuting operator correlations.

Contribution

It demonstrates that independent detectors can improve measurement efficiency and violate the Korotkov-Averin bound via cross-correlations, and examines deviations in mesoscopic conductors.

Findings

Twin detectors achieve maximal efficiency in single-shot measurements.

Cross-correlations enable violation of the Korotkov-Averin bound.

Vanishing noise background tests ideal detector independence.

Abstract

We investigate the advantages of using two independent, linear detectors for continuous quantum measurement. For single-shot quantum measurement, the measurement is maximally efficient if the detectors are twins. For weak continuous measurement, cross-correlations allow a violation of the Korotkov-Averin bound for the detector's signal-to-noise ratio. A vanishing noise background provides a nontrivial test of ideal independent quantum detectors. We further investigate the correlations of non-commuting operators, and consider possible deviations from the independent detector model for mesoscopic conductors coupled by the screened Coulomb interaction.