Protective measurements of photon polarization using a temporal pointer

TL;DR

This paper experimentally demonstrates protective measurements of photon polarization by weakly coupling it to a temporal pointer, using an optical loop to control multiple protection and measurement stages, revealing expectation values without prior state knowledge.

Contribution

It introduces an experimental implementation of protective measurements on single photons using a temporal pointer and variable protection stages, advancing quantum measurement techniques.

Findings

Successfully measured photon polarization expectation values without prior state knowledge

Implemented variable protection and measurement stages (1-9) using an optical loop

Confirmed that protective measurements provide genuine information gain

Abstract

We experimentally demonstrate protective measurements by weakly coupling the polarization of a single-photon-level field to a measurement pointer that corresponds to the arrival time of the photon. By using an optical loop, we implement a variable, controlled number (1-9) of protection and measurement stages. We demonstrate the measurement of expectation values of photon polarization by measuring arrival times while simultaneously protecting the polarization state. No knowledge of the initial photon state is required or available in our experiment, demonstrating that protective measurements provide a genuine information gain that cannot simply be reduced to a priori information about the protection procedure.