Observation of quantum effects on radiation reaction in strong fields

TL;DR

This paper reports the first high-significance experimental observation of quantum radiation reaction effects on electrons in strong fields, providing evidence favoring quantum models over classical predictions.

Contribution

It presents the first quantitative, high-significance experimental validation of quantum radiation reaction models in strong fields, using a novel Bayesian model comparison framework.

Findings

Quantum effects significantly influence electron spectra in strong fields.

Quantum models outperform classical models in predicting electron energy losses.

A novel Bayesian framework effectively compares models in laser-particle experiments.

Abstract

Radiation reaction, the force experienced by an accelerated charge due to radiation emission, has long been the subject of extensive theoretical and experimental research. Experimental verification of a quantum, strong-field description of radiation reaction is fundamentally important, and has wide-ranging implications for astrophysics, laser-driven particle acceleration, next-generation particle colliders and inverse-Compton photon sources for medical and industrial applications. However, the difficulty of accessing regimes where strong field and quantum effects dominate inhibited previous efforts to observe quantum radiation reaction in charged particle dynamics with high significance. We report the first high significance (> 5{\sigma}) observation of strong-field radiation reaction on electron spectra where quantum effects are substantial. We obtain the first, quantitative, strong evidence favouring the quantum-continuous and quantum-stochastic models over the classical model; the quantum models perform comparably. The lower electron energy losses predicted by the quantum models accounts for their improved performance. Model comparison was performed using a novel Bayesian framework which has widespread utility for laser-particle collision experiments, including those utilising conventional accelerators, where some collision parameters cannot be measured directly.