Decoherence puzzle in measurements of photons originating from electron-positron annihilation

Abstract

Entanglement of photons originating from the electron-positron annihilation has not been proven experimentally. Though the independent experiments performed so far unanimously confirm that correlation between the linear polarizations of back-to-back photons from the electron-positron annihilation is consistent with the assumption that these photons are entangled in polarization. Yet, unexpectedly, recent experiments differ as regards the correlation of polarization direction of back-to-back photons after the decoherence induced by scattering of one of these photons on the electron in the scattering material. In one of the experiments the correlation before and after the decoherence of the photon state is the same and in the other experiment the scattering of one photon leads to a significant decrease of this correlation. Here we discuss this puzzle. The separable states were ensured by forcing one of the annihilation photons through prior scattering before the Compton kinematics-based measurement of the polarization correlation. A comparison between the experimental setups used for the different measurements and the results obtained are briefly discussed, highlighting the parameters that are important for performing such measurements. Finally, the main features of the J-PET detector are presented with the schemes for performing similar measurements so that the results can be used as conclusive remarks for solving this puzzle. Solving of these puzzle will have crucial consequences for basic studies of entanglement and also for the proposed application of polarisation of photons in positron emission tomography. In case if the correlation of polarisation of back-to-back photons from the electron-positron annihilation is the same before and after the scattering of these photons, then it will not be useful for the reduction of the scatter fraction in PET diagnostics.

Experimental observation of polarization correlation of entangled photons from positronium atom using J-PET detector

“…The primary objective of this experiment is to observe and confirm the polarization correlation of entangled photons originating from the decays of Ps atom by measuring the angle between the scattering planes of the annihilation photons. For the determination of scattering plane, momenta direction of annihilation photons before and after the scattering have to be estimated [7].…”