Weak Measurement of Qubit Oscillations with Strong Response Detectors: Violation of the Fundamental Bound Imposed on Linear Detectors

TL;DR

This paper demonstrates that in the nonlinear response regime, solid-state qubit measurements can surpass the quantum limit on signal-to-noise ratio set for linear detectors, using cross-correlation analysis.

Contribution

It reveals a violation of the fundamental quantum bound for linear detectors by employing nonlinear response in solid-state qubit measurements.

Findings

Signal-to-noise ratio exceeds the quantum limit in nonlinear regime

Cross-correlation explains the violation of the bound

Solid-state qubit measurement can outperform linear detectors

Abstract

We investigate the continuous weak measurement of a solid-state qubit by single electron transistors in nonlinear response regime. It is found that the signal-to-noise ratio can violate the universal upper bound imposed quantum mechanically to any linear response detectors. We understand the violation by means of the cross-correlation of the detector currents.