Quantum information approach to high energy interactions

High energy hadron interactions are commonly described by using a probabilistic parton model that ignores quantum entanglement present in the light-cone wave functions. Here, we argue that since a high energy interaction samples an instant snapshot of the hadron wave function, the phases of different Pock state wave functions cannot be measured-therefore the light-cone density matrix has to be traced over these unobservable phases. Performing this trace with the corresponding U(1) Haar integration measure leads to 'Haar scrambling' of the density matrix, and to the emergence of entanglement entropy. This entanglement entropy is determined by the Fock state probability distribution, and is thus directly related to the parton structure functions. As proposed earlier, at large rapidity eta the hadron state becomes maximally entangled, and the entanglement entropy is S-E( )similar to eta according to QCD evolution equations. When the phases of Fock state components are controlled, for example in spin asymmetry measurements, the Haar average cannot be performed, and the probabilistic parton description breaks down. This article is part of the theme issue 'Quantum technologies in particle physics'.

Automated summary

This article discusses quantum entanglement in high energy hadron interactions and proposes a Haar trace of the light-cone density matrix to explain the emergence of entanglement entropy. The research reveals a direct relationship between entanglement entropy and parton structure functions, with maximal entanglement at large rapidity. The probabilistic parton model breaks down when controlling the phases of Fock state components.