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IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC)

Quantum entangled PET - recent progress and new insights

Daniel P. Watts

Published Sep 25, 2024• 1 citation
Publisher

Abstract

Exploitation of the implicit quantum entanglement (QE) of the two gamma-photons in PET for improving image quality is a novel new methodology proposed only recently e.g [1]. However progress in this new area had been hindered due to lack of theoretical understanding or experimental constraint on how the initial QE can be dispersed to the envirionment through decoherence. Such processes will have significant role in PET imaging through scatter processes in the patient, bed or the detector crystals. The role of such processes will be significantly enhanced in next-generation fully body PET.Addressing this major gap in our knowledge of QE decoherence is a key aim of the new MeVQE collaboration, an interdisciplinary grouping of nuclear physicists, quantum information theorists and mathematicians based at the University of York. The first theoretical calculation of the decoherence of QE for PET photons will be presented [2]. Predictions from the new theory are challenged with a first detailed experimental determination of the triple Compton scattering of entangled gamma photons [3]. The work provides a paradigm shift in our understanding of QE decoherence for PET photons. In addition a further key measurement for the field will be presented, the first determination of the QE witness in a relistic preclinical scenario viz. 18-F source with gamma produced from annihilation in tissue (mouse heart). The future programme of MeVQE in establishing QEPET will also be outlined.

DOI
10.1109/nss/mic/rtsd57108.2024.10658587

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Exploitation of the implicit quantum entanglement (QE) of the two gamma-photons in PET for improving image quality is a novel new methodology proposed only recently e.g [1]. However progress in this new area had been hindered due to lack of theoretical understanding or experimental constraint on how the initial QE can be dispersed to the envirionment through decoherence. Such processes will have significant role in PET imaging through scatter processes in the patient, bed or the detector crystals. The role of such processes will be significantly enhanced in next-generation fully body PET.Addressing this major gap in our knowledge of QE decoherence is a key aim of the new MeVQE collaboration, an interdisciplinary grouping of nuclear physicists, quantum information theorists and mathematicians based at the University of York. The first theoretical calculation of the decoherence of QE for PET photons will be presented [2]. Predictions from the new theory are challenged with a first detailed experimental determination of the triple Compton scattering of entangled gamma photons [3]. The work provides a paradigm shift in our understanding of QE decoherence for PET photons. In addition a further key measurement for the field will be presented, the first determination of the QE witness in a relistic preclinical scenario viz. 18-F source with gamma produced from annihilation in tissue (mouse heart). The future programme of MeVQE in establishing QEPET will also be outlined.
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.
Positron Emission Tomography (PET) is a widely-used imaging modality for medical research and clinical diagnosis. Imaging of the radiotracer is obtained from the detected hit positions of the two positron annihilation photons in a detector array. The image is degraded by backgrounds from random coincidences and in-patient scatter events which require correction. In addition to the geometric information, the two annihilation photons are predicted to be produced in a quantum-entangled state, resulting in enhanced correlations between their subsequent interaction processes. To explore this, the predicted entanglement in linear polarisation for the two photons was incorporated into a simulation and tested by comparison with experimental data from a cadmium zinc telluride (CZT) PET demonstrator apparatus. Adapted apparati also enabled correlation measurements where one of the photons had undergone a prior scatter process. We show that the entangled simulation describes the measured correlations and, through simulation of a larger preclinical PET scanner, illustrate a simple method to quantify and remove the unwanted backgrounds in PET using the quantum entanglement information alone.
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Constraints on the quantum decoherence of entangled γ quanta at the mega-electron-volt scale, such as those produced following positron annihilation, have remained elusive for many decades. We present the first statistically and kinematically precise experimental data for triple Compton scattering of such entangled γ. An entanglement witness (R), relating to the enhancement of the azimuthal correlation between the final scattering planes, is obtained where one of the γ underwent intermediate Compton scattering. The measured R, deconvolved from multiple scattering backgrounds, are found to exceed the classical limit for intermediate scatter angles up to ∼60° and diminish at larger angles. The data are consistent with predictions from a first quantum theory of entangled triple Compton scattering as well as a simple model based approach. The results are crucial to future study and utilization of entangled mega-electron-volt γ in fundamental physics and positron emission tomography imaging.
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.
This theoretical research aims to examine areas of the Compton cross section of entangled annihilation photons for the purpose of testing for possible break down of theory, which could have consequences for predicted optimal capabilities of Compton PET systems. We provide maps of the cross section for entangled annihilation photons for experimental verification. We introduce a strategy to derive cross sections in a relatively straight forward manner for the Compton scattering of a hypothetical separable, mixed and entangled states. To understand the effect that entanglement has on the cross section for annihilation photons, we derive the cross section so that it is expressed in terms of the cross section of a hypothetical separable state and of a hypothetical forbidden maximally entangled state. We find lobe-like structures in the cross section which are regions where entanglement has the greatest effect. We also find that mixed states do not reproduce the cross section for annihilation photons, contrary to a recent investigation which reported otherwise. We review the motivation and method of the most precise Compton scattering experiment for annihilation photons, in order to resolve conflicting reports regarding the extent to which the cross section itself has been experimentally verified.