Heisenberg scaling with weak measurement: A quantum state discrimination point of view

TL;DR

This paper analyzes the Heisenberg scaling in weak measurement-based quantum metrology, highlighting the importance of spin state measurement, the impact of dephasing noise, and comparing different measurement interactions.

Contribution

It provides a quantum state discrimination perspective on Heisenberg scaling in weak measurements and examines noise effects and measurement types affecting precision.

Findings

Heisenberg scaling relates to orthogonal state rotation via interaction

Precision degrades rapidly under dephasing noise

Von Neumann measurement interactions exhibit similar effects

Abstract

We examine the results of the paper "Precision metrology using weak measurements", [Zhang, Datta, and Walmsley, arXiv:1310.5302] from a quantum state discrimination point of view. The Heisenberg scaling of the photon number for the precision of the interaction parameter between coherent light and a spin one-half particle (or pseudo-spin) has a simple interpretation in terms of the interaction rotating the quantum state to an orthogonal one. In order to achieve this scaling, the information must be extracted from the spin rather than from the coherent state of light, limiting the applications of the method to phenomena such as cross-phase modulation. We next investigate the effect of dephasing noise, and show a rapid degradation of precision, in agreement with general results in the literature concerning Heisenberg scaling metrology. We also demonstrate that a von Neumann-type measurement interaction can display a similar effect.