What does a scattering process know? High-energy physicists have long catalogued cross sections and decay rates, but a complementary question has only recently come into focus: how much (and what kind of) quantum information is generated when elementary particles interact? Inspired by Wheeler's “It from bit” hypothesis, which suggests that information may be as fundamental to physics as energy and momentum, this thesis pursues a systematic characterization of the quantum information content of scattering amplitudes in quantum electrodynamics (QED).
Beyond philosophical motivation, in recent years, quantum information observables are been measured in colliders [1] and the quantum information content of the interactions are being used as probes for Beyond the Standard Model phenomena [2]. More strikingly, some works are finding the emergence of certain symmetries and predictions of interaction’s free parameters by imposing certain properties to these quantum information observables [3].Â
The goal of this project is to understand the quantum information content in scattering processes governed by QED. We will begin at tree level, where the helicity degrees of freedom of the scattered particles form a natural qubit system [3,4,5]. For the paradigmatic two-to-two processes we will compute the scattering amplitudes and reconstruct the density matrix of the outgoing particles. Then, quantities such as entanglement entropy, concurrence or stabilizer Renyi entropies can be computed. These figures of merit quantify the “quantumness” of the process and can gauge the irreducibly quantum character of the interaction in a resource-theoretic sense. In other words, how far are they to be described efficiently by a classical theory or simulation.
There are several extensions to this project that can be explored next. In the tree level scenario, we can extend the formalism to the multi-partite case (i.e. more than two outgoing particles) with processes such as orthopositronium decay to three photons. Another possible extension is analyzing the one-loop correction to the quantum information observables computed. A third possibility is considering interactions beyond QED, e.g. QCD (quark scattering) or weak interactions (e.g. lepton-lepton scattering through a Z boson). No prior knowledge of quantum information theory is assumed or required.