Bell Test of Photons from Electron-Positron Annihilation via POVM-based Compton Polarimetry

TL;DR

This paper develops a POVM-based framework for high-energy photon polarization measurements via Compton polarimetry, enabling the potential experimental demonstration of quantum entanglement in gamma-ray photons.

Contribution

It introduces a novel POVM model for high-energy photon polarization measurements and shows how repeated interactions improve measurement accuracy toward ideal projective measurements.

Findings

Measurement convergence toward ideal polarization with increasing interactions.

Framework enables potential violation of CHSH inequalities with gamma-ray photons.

Addresses the challenge of verifying quantum entanglement in high-energy photons.

Abstract

Quantum entanglement between gamma-ray photons emitted following electron-positron annihilation is expected to be maximal and may be characterized via non-classical polarization correlations. However, this is difficult to verify experimentally because there are no established schemes that approach ideal projective-polarization measurements for high-energy photons. Hence, polarization entanglement between MeV-scale annihilation photons has not yet been conclusively demonstrated. We develop here a framework that models polarization measurements of high-energy photons via Compton polarimetry, employing the formalism of positive operator-valued measures (POVMs). We extend the POVM description to sequences of repeated interactions and show that the measurement converges toward an ideal projective measurement of linear polarization as the number of interactions increases. We demonstrate that this progressive improvement in measurement sharpness can enable the experimental violation of CHSH inequalities.