Measuring small longitudinal phase shifts: weak measurements or standard interferometry?

TL;DR

This paper compares weak measurements and standard interferometry for detecting small longitudinal phase shifts, finding standard methods superior in some cases but proposing a scheme that could vastly outperform them using imaginary weak values.

Contribution

The paper demonstrates the limitations of weak measurements for longitudinal phase shifts and introduces a novel interferometric scheme leveraging imaginary weak values for enhanced sensitivity.

Findings

Standard interferometry outperforms weak measurements with real weak values.

A new interferometric scheme with imaginary weak values shows potential for significant sensitivity improvements.

The proposed method could outperform traditional techniques by several orders of magnitude.

Abstract

Recently, weak measurements were used to measure small effects that are transverse to the propagation direction of a light beam. Here we address the question whether weak measurements are also useful for measuring small longitudinal phase shifts. We show that standard interferometry greatly outperforms weak measurements in a scenario involving a purely real weak value. However, we also present an interferometric scheme based on a purely imaginary weak value, combined with a frequency-domain analysis, which may have potential to outperform standard interferometry by several orders of magnitude.