Dressed infrared quantum information

TL;DR

The paper addresses infrared divergences in QED by employing the Chung–Kibble–Faddeev–Kulish dressed-state formalism to construct an infrared-finite $S$-matrix. It shows that measurements restricted to electronic degrees of freedom experience decoherence in momentum space due to unobserved soft photons, quantified by a damping factor that matches the inclusive formalism, even though the dressed approach avoids explicit soft-photon tracing. The authors provide concrete calculations for one- and multi-particle scattering, discuss physical interpretations and connections to asymptotic charges and superselection rules, and relate the findings to the black hole information problem, including compatibility with Strominger's soft-particle purification idea. The work thus links infrared structure in gauge theories to quantum information concepts and highlights potential implications for perturbative gravity.

Abstract

We study information-theoretic aspects of the infrared sector of quantum electrodynamics, using the dressed-state approach pioneered by Chung, Kibble, Faddeev-Kulish and others. In this formalism QED has an IR-finite S-matrix describing the scattering of electrons dressed by coherent states of photons. We show that measurements sensitive only to the outgoing electronic degrees of freedom will experience decoherence in the electron momentum basis due to unobservable photons in the dressing. We make some comments on possible refinements of the dressed-state formalism, and how these considerations relate to the black hole information paradox.

Figures (1)

• Figure 1: Diagrams contributing to the dressed scattering with additional bremsstrahlung. The first two diagrams correspond to mixing of the emitted photon and dressing photons (circles), while the latter two diagrams correspond to the usual Feynman diagrams where the photon is emitted from the electron lines.