Measuring Entanglement of Electron-Positron Annihilation Gammas Using Circular Polarization Analyzers*

    The gamma rays from electron-positron annihilation are in an entangled state. The associated quantum contextuality inequality for this system was measured using the polarization dependence of Compton scattering for the two correlated gammas [1]. It has been argued that this measurement does not constitute a true Bell inequality test since the measured observables commute [2]. We present a version of this experiment which employs circular polarization analyzers to avoid this loophole. We also observe that the original version of this experiment involving linear polarization is now well-suited for a senior physics undergraduate lab involving quantum entanglement [3]. 

    [1] L. R. Kasday, J. Ullman, and C. S. Wu, Il Nuovo Cimento B25, 2 (1975).

    [2] S. A. Abel, M. Dittmar, H. Dreiner, Phys. Lett. B280, 304 (1992).

    [3] J. Engbrecht and N. Hillson, Am. J. Phys.86, 549 (2018).