First Detailed Study of the Quantum Decoherence of Entangled Gamma Photons

Constraints on the quantum decoherence of entangled <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>γ</a:mi></a:math> 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 <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>γ</c:mi></c:math>. An entanglement witness (<e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mi>R</e:mi></e:math>), relating to the enhancement of the azimuthal correlation between the final scattering planes, is obtained where one of the <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mi>γ</g:mi></g:math> underwent intermediate Compton scattering. The measured <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mi>R</i:mi></i:math>, deconvolved from multiple scattering backgrounds, are found to exceed the classical limit for intermediate scatter angles up to <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mo>∼</k:mo><k:mn>60</k:mn><k:mi>°</k:mi></k:math> 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 <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mi>γ</m:mi></m:math> in fundamental physics and positron emission tomography imaging.