Non-maximal entanglement of photons from positron-electron annihilation demonstrated using a novel plastic PET scanner

TL;DR

This study introduces a novel plastic PET scanner capable of measuring photon polarization, revealing that photons from positron-electron annihilation are not maximally entangled, which depends on the annihilation process.

Contribution

A new plastic scintillator-based PET scanner that measures photon polarization and demonstrates the non-maximal entanglement of annihilation photons based on their origin.

Findings

Photons from pick-off annihilation are not entangled.

Photons from direct and para-positronium annihilations are maximally entangled.

Degree of entanglement varies with annihilation mechanism.

Abstract

In state-of-the-art Positron Emission Tomography (PET), information about annihilation photon polarization is unavailable. Here, we present a PET scanner built from plastic scintillators, where annihilation photons primarily interact via the Compton effect, providing information about both photon polarization and propagation direction. Using this plastic-based PET, we determined the distribution of the relative angle between polarization planes of photons from positron-electron annihilation in a porous polymer. The amplitude of the observed distribution is smaller than predicted for maximally quantum-entangled two-photon states but larger than expected for separable photons. This result can be well explained by assuming that photons from pick-off annihilation are not entangled, while photons from direct and para-positronium annihilations are maximally entangled. Our result indicates that the degree of entanglement depends on the annihilation mechanism in matter, opening new avenues for exploring polarization correlations in PET as a diagnostic indicator.