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Optica Acta International Journal of Optics

The Photon Anticorrelation Effect in the Stimulated Annihilation Process of Electron-positron Pairs

C. Sibilia, M. Bertolotti

Published Apr 1, 1981• 6 citations
Publisher

Abstract

The photon anticorrelation effect has been demonstrated for many non-linear optical processes. We wish to show that the effect can also occur in the two n -rays produced by stimulated emission from electron-positron pair recombination. In this process anticorrelation occurs between the stimulated modes in which the two n -photons are emitted, but only in the short-time approximation. The effect turns out to be independent of the phase of the fields and is of a purely quantum-mechanical nature.

DOI
10.1080/713820586

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The photon anticorrelation effect has been demonstrated for many non-linear optical processes. We wish to show that the effect can also occur in the two n -rays produced by stimulated emission from electron-positron pair recombination. In this process anticorrelation occurs between the stimulated modes in which the two n -photons are emitted, but only in the short-time approximation. The effect turns out to be independent of the phase of the fields and is of a purely quantum-mechanical nature.
Recent experimental measurements of the time interval between detection of the two photons emitted in positron-electron annihilation have indicated that collapse of the spatial part of the photon's wave function, due to detection of the other photon, does not occur. Although quantum nonlocality actually occurs in photons produced through parametric down-conversion, the recent experiments give strong evidence against measurement-induced instantaneous spatial localization of high-energy $\ensuremath{\gamma}$ photons. A quantum-mechanical analysis of the Einstein-Podolsky-Rosen problem is presented, which may help to explain the observed differences between photons produced through parametric down-conversion and photons produced through positron-electron annihilation. The results are found to concur with the recent experiments involving $\ensuremath{\gamma}$ photons.
When a positron/electron pair annihilate via the two-photon pathway, the emitted photons are momentum correlated. This correlation ensures that they move along a straight line path in opposite directions. An experiment performed in 2004 by Dr. V.D. Irby measured the time interval between \ndetection of the photons. He observed a decay in the number of counts with increasing detection time interval, which he described using a Lorentzian, the line width of which at full-width half-maximum is \nmeasured to be 120ps. The data collected by Irby is interesting because current theory predicts that because the source is so localized (the effective source width used by Irby is safely within 5rnrn) the photons should be detected within a time interval of ?t=d/c where d is the thickness of the source. This time interval corresponds to 17ps. This thesis fits the results to an exponential, and shows that this exponentially decaying nature of the coincidence time interval is characteristic of the entanglement of the two photons. We find that the wavefunctions of the photons decoheres in space according to how long the particle pair took to decay (which is exponential), and that the probability of simultaneous \ndetection depends on the exponential of the product of the lifetime of positronium and the detection time interval.
Recent experimental measurements of the time interval between detection of the two photons emitted in positron-electron annihilation have indicated that collapse of the spatial part of the photon's wave function, due to detection of the other photon, does not occur. Although quantum nonlocality actually occurs in photons produced through parametric down-conversion, the recent experiments give strong evidence against measurement-induced instantaneous spatial localization of high-energy $\ensuremath{\gamma}$ photons. A quantum-mechanical analysis of the Einstein-Podolsky-Rosen problem is presented, which may help to explain the observed differences between photons produced through parametric down-conversion and photons produced through positron-electron annihilation. The results are found to concur with the recent experiments involving $\ensuremath{\gamma}$ photons.
The entanglement of photons originating from electron-positron annihilation has not been experimentally proven.owever, the independent experiments performed so far unanimously confirm that the correlation between the linear polarizations of back-to-back photons from electron-positron annihilation is consistent with the assumption that these photons are entangled in the polarization.Yet, unexpectedly, recent experiments differ as regards the correlation of polarization direction of back-to-back photons after the decoherence induced by the 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 in this correlation.Here we discuss this puzzle.Decoherent states were ensured provided by forcing one of the annihilation photons to scatter earlier before measuring the polarization correlation based on Compton kinematics.The comparison is made between the experimental setups used for the different measurements, and the results obtained are briefly discussed, highlighting the parameters that are important in performing such measurements.Finally, the main features of the J-PET detector are presented, along with the schemes for performing similar studies, so that the conclusive results can be used as remarks to solve the puzzle in question.Solving the decoherence puzzle will have crucial consequences for basic studies of entanglement, as well as for the proposed application of the photon polarization in positron emission tomography.If the correlation of the polarization 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 scatter fraction in positron emission tomography diagnostics.