Error-disturbance uncertainty relations in Faraday measurements

TL;DR

This paper investigates error-disturbance relations in quantum spin measurements using atom-light interactions, revealing violations of Heisenberg-Arthurs-Kelly bounds and confirming the validity of Branciard-Ozawa relations, with implications for quantum metrology.

Contribution

It introduces a detailed analysis of error and disturbance in Faraday-based spin measurements, including effects of polarization squeezing and weak interactions, advancing understanding of quantum measurement limits.

Findings

Heisenberg-Arthurs-Kelly relation is violated in these measurements.

Branciard-Ozawa uncertainty relation always holds in the studied scenarios.

Weak interactions restore the unbiasedness condition and the Heisenberg-Arthurs-Kelly relation.

Abstract

We examine error-disturbance relations in the quantum measurement of spin systems using an atom-light interface scheme. We model a single spin-1/2 system that interacts with a polarized light meter via a Faraday interaction. We formulate the error and disturbance of the model and examine the uncertainty relations. We found that for the coherent light meter in pure polarization, both the error and disturbance behave the cyclic oscillations due to the Faraday rotation in both the light and spin polarizations. We also examine a class of polarization squeezed light meter, where we apply the phase-space approximation and characterize the role of squeezing. We derive error-disturbance relations for these cases and find that the Heisenberg-Arthurs-Kelly uncertainty is violated while the tight Branciard-Ozawa uncertainty always holds. We note that, in the limit of weak interaction strength, the error and disturbance become to obey the unbiasedness condition and hence the Heisenberg-Arthurs-Kelly relation holds. The work would contribute to our understanding of quantum measurement of spin systems under the atom-light interface framework, and may hold potential applications in quantum metrology, quantum state estimation and control.