Setup of Compton polarimeters for measuring entangled annihilation photons

Abstract

An experimental setup for studying the Compton scattering of annihilation photons in various (entangled and decoherent) quantum states is presented. Two entangled γ-quanta with an energy of 511 keV and mutually orthogonal polarizations are produced by positron-electron annihilation in a thin aluminum plate and are emitted in opposite directions. To measure both photons, the setup provides two equivalent arms of Compton polarimeters. A Compton polarimeter consists of a plastic scintillation scatterer and an array of NaI(Tl) detectors for measuring photons deflected at an angle of 90°. The intermediate scatterer of the GAGG scintillator with SiPM readout is inserted into one of the arms to create a tagged decoherence process prior to the measurement of annihilation photons in polarimeters. The performance of Compton scatterers and NaI(Tl) counters is discussed. The polarization modulation factor and the analyzing power of Compton polarimeters are evaluated from the angular distributions of scattered gammas. The Compton scattering of photons in entangled and decoherent states is compared reliably for the first time.

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

“…It is worth mentioning that the obtained results [16] do not agree with the theoretical predictions [19]. Recently, Abdurashitove et al [17], reported experimental results that contradicted those of obtained by Watts et al [16]. The experiments were performed using the same methodology: (a) when their relative linear polarization was considered to be entangled (direct Compton kinematics applied to backto-back photons to measure the correlation), (b) inducing decoherence in the polarization entanglement, using the scatterer along the path of one of the photons, and calculating the effect on the measured correlation.…”

“…In this study, the scattering angle range was 80 0 < θ 1 = θ 2 < 100 0 for both cases. Details of the experiments can be found in the respective publications [16,17] It should be emphasised that in the work of Abdurashitov et al [17], no difference in the µ distribution was observed for the entangled and separable quantum states, indicating that the Compton kinematics remained identical for both cases as predicted in [19]. Fig.…”

“…For a photon of energy 511 keV scattering at θ = 82 0 the value of A = α(θ ) reaches a maximum (A=0.69). Probability of Compton scatterings of two mutually orthogonal polarization scattering at angles θ 1 and θ 2 following in terms of analysing power of Compton parameters can be written as [17]:…”

“…For the data presented here, a scattering angle range of 70 0 < θ 1 = θ 2 < 110 0 was chosen to investigate the entangled state hypothesis, while 60 0 < θ 1 = θ 2 < 140 0 was chosen for the separable state. The bottom panel shows the results of [17] for two different states. In this study, the scattering angle range was 80 0 < θ 1 = θ 2 < 100 0 for both cases.…”

“…Moreover, they also determined the exact value of the upper limit for the separable state of 1.63 by introducing the correction into the formula derived in the Bohm paper (supplementary note in DP watts et al [16]). In contrast, Abdurshitov et al [17], reported that re-gardless of the initial state (entangled or separable (decohernce)) of the annihilation photons, the same polarization correlation distribution was measured. This left open the question of whether the measured correlation between the polarization of annihilation photons can be considered a unique signature for distinguishing the origin of annihilation photons from entangled or separable states.…”