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Science Advances

Nonmaximal entanglement of photons from positron-electron annihilation demonstrated using a plastic PET scanner

Paweł Moskal, Deepak Kumar, Sushil K. Sharma, E. Beyene, N. Chug, Aurélien Coussat, Catalina Curceanu, E. Czerwiński, Manish Das, K. Dulski, Marek Gorgol, B. Jasinska, K. Kacprzak, T. Kaplanoglu, Ł. Kapłon, T. Kozik, Edward Lisowski, Filip Lisowski, W. Mryka, Szymon Niedźwiecki, S. Parzych, E. Pérez del Río, Martin Rädler, M. Skurzok, Ewa Łucja Stępień, P. Tanty, Keyvan Tayefi Ardebili, Kavya Valsan Eliyan

Published May 1, 2025• 27 citations
Publisher

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 parapositronium annihilations are maximally entangled. Our result indicates that the degree of entanglement depends on the annihilation mechanism in matter, opening avenues for exploring polarization correlations in PET as a diagnostic indicator.

DOI
10.1126/sciadv.ads3046

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Annihilation photons are quantum-entangled in polarization, a phenomenon that has not been exploited in medical diagnostics so far. We present the first in vivo imaging of the degree of quantum entanglement of photons originating from positron-electron annihilation within a human subject. This study utilized the Jagiellonian Positron Emission Tomography (J-PET) scanner, constructed from plastic scintillators. In plastics, annihilation photons interact primarily via the Compton effect, which provides simultaneous information regarding the photon interaction position and time, as well as the photon polarization plane. The patient was injected with a DOTA-TATE radiopharmaceutical labeled with the $^{68}$Ga radionuclide. Using the J-PET scanner, we determined the image of the radiopharmaceutical uptake and, simultaneously, the image of the degree of quantum entanglement. The latter was determined from the relative angle between the polarization planes of the annihilation photons. The values of the degree of quantum entanglement extracted for the liver and the spleen are smaller than those predicted for maximally entangled two-photon states, yet larger than expected for separable photons. This demonstration opens new perspectives for the application of quantum entanglement in clinical diagnostics.

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Annihilation photons are quantum entangled in their polarization, a property that is not accessible in state-of-the-art clinical Positron Emission Tomography (PET). This roadmap describes the current status of research in the emerging field of quantum entanglement applications involving these photons for medical diagnosis. It outlines the underlying physics phenomena and the development of detector systems that can serve as a foundation for future Quantum Entanglement PET (QE-PET) scanners. These scanners will be capable of utilizing the entanglement between annihilation photons by measuring their Compton scattering on electrons. This roadmap comprises up-to-date experimental results on the study of quantum entanglement and the decoherence of annihilation photons, alongside the current theoretical understanding of these phenomena. The methods and detector technologies described herein are being developed (i) in order to enhance standard PET imaging by suppressing random coincidences in the reconstruction of annihilation site density distributions, (ii) in order to establish the degree of quantum entanglement as a diagnostic biomarker for tissue pathology and oxygenation, and (iii) in order to elaborate a method for pH imaging. Whether entanglement-based imaging and pH mapping can be successfully translated into clinical practice remains an open question and a subject of exciting ongoing research. This roadmap serves as an invitation to the scientific community to join this burgeoning field.

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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.

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Deepak Kumar, Sushil Kumar Sharma, Paweł Moskal

Quantum entanglement is one of the fundamental correlations between particles that has not yet been confirmed with high-energy photons. Quantum electrodynamics (QED) predicts that annihilation photons produced by the decay of the singlet state of positronium (Ps) atoms are entangled in their polarization. Since these photons have an energy of 511 keV, there is no polarizer to measure the polarization of these photons. However, the direction of the scattering photons when interacting with an electron via the Compton process depends strongly on the polarization of the photon. Therefore, Compton scattering can be used as a polarization analyser. The polarization direction of the photon can be defined as the cross product of the momentum vector of the incident and scattered photon. By measuring the polarization of annihilation photons originating from Ps decays, their polarization correlation can be determined. Measuring this correlation will for the first time, will answer the open question of studying quantum entanglement in high-energy photons. Moreover, it also have potential applications in PET imaging, where the quality of image reconstruction directly depends on the selection of pure annihilation photons, which can be separated based on the strength of the polarization correlation. In this paper, we report on the method for determining the polarization correlation of annihilation photons using the J-PET detector.

European Physical Society Conference on High Energy Physics (EPS-HEP)•Dec 14, 2023•2 citations
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 parapositronium annihilations are maximally entangled. Our result indicates that the degree of entanglement depends on the annihilation mechanism in matter, opening avenues for exploring polarization correlations in PET as a diagnostic indicator.
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.
Abstract Quantum electrodynamics (QED) predicts that photons from positronium decay are maximally entangled. However, experimental verification of this entanglement in high-energy photons has remained elusive due to competing decay processes and interactions with the surrounding medium. The J-PET detector is a multi-modules detector based on plastic scintillators that has the potential to measure such correlation in the whole phase space. Photons interact with plastic mainly via Compton scattering, which makes J-PET particularly suitable for this type of study. Moreover, by incorporating the positron lifetime as an additional parameter, to differentiate between various decay processes and examine how the polarization correlation changes as a function of lifetime. Such studies provide new insights into quantum entanglement at high energy regimes and hold potential to enhance positron emission tomography (PET) imaging techniques. Recent results demonstrate the J-PET detector’s capability to measure the polarization correlation of photons emitted from positron annihilation in a porous medium. In this paper, we present a review of past research in this field, highlighting the need for further investigation of polarization correlation of annihilation photons.
Annihilation photons are quantum-entangled in polarization, a phenomenon that has not been exploited in medical diagnostics so far. We present the first in vivo imaging of the degree of quantum entanglement of photons originating from positron-electron annihilation within a human subject. This study utilized the Jagiellonian Positron Emission Tomography (J-PET) scanner, constructed from plastic scintillators. In plastics, annihilation photons interact primarily via the Compton effect, which provides simultaneous information regarding the photon interaction position and time, as well as the photon polarization plane. The patient was injected with a DOTA-TATE radiopharmaceutical labeled with the 68^{68}68Ga radionuclide. Using the J-PET scanner, we determined the image of the radiopharmaceutical uptake and, simultaneously, the image of the degree of quantum entanglement. The latter was determined from the relative angle between the polarization planes of the annihilation photons. The values of the degree of quantum entanglement extracted for the liver and the spleen are smaller than those predicted for maximally entangled two-photon states, yet larger than expected for separable photons. This demonstration opens new perspectives for the application of quantum entanglement in clinical diagnostics.
Annihilation photons are quantum entangled in their polarization, a property that is not accessible in state-of-the-art clinical Positron Emission Tomography (PET). This roadmap describes the current status of research in the emerging field of quantum entanglement applications involving these photons for medical diagnosis. It outlines the underlying physics phenomena and the development of detector systems that can serve as a foundation for future Quantum Entanglement PET (QE-PET) scanners. These scanners will be capable of utilizing the entanglement between annihilation photons by measuring their Compton scattering on electrons. This roadmap comprises up-to-date experimental results on the study of quantum entanglement and the decoherence of annihilation photons, alongside the current theoretical understanding of these phenomena. The methods and detector technologies described herein are being developed (i) in order to enhance standard PET imaging by suppressing random coincidences in the reconstruction of annihilation site density distributions, (ii) in order to establish the degree of quantum entanglement as a diagnostic biomarker for tissue pathology and oxygenation, and (iii) in order to elaborate a method for pH imaging. Whether entanglement-based imaging and pH mapping can be successfully translated into clinical practice remains an open question and a subject of exciting ongoing research. This roadmap serves as an invitation to the scientific community to join this burgeoning field.
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.
Quantum entanglement is one of the fundamental correlations between particles that has not yet been confirmed with high-energy photons. Quantum electrodynamics (QED) predicts that annihilation photons produced by the decay of the singlet state of positronium (Ps) atoms are entangled in their polarization. Since these photons have an energy of 511 keV, there is no polarizer to measure the polarization of these photons. However, the direction of the scattering photons when interacting with an electron via the Compton process depends strongly on the polarization of the photon. Therefore, Compton scattering can be used as a polarization analyser. The polarization direction of the photon can be defined as the cross product of the momentum vector of the incident and scattered photon. By measuring the polarization of annihilation photons originating from Ps decays, their polarization correlation can be determined. Measuring this correlation will for the first time, will answer the open question of studying quantum entanglement in high-energy photons. Moreover, it also have potential applications in PET imaging, where the quality of image reconstruction directly depends on the selection of pure annihilation photons, which can be separated based on the strength of the polarization correlation. In this paper, we report on the method for determining the polarization correlation of annihilation photons using the J-PET detector.