Vacuum birefringence at x-ray free-electron lasers

TL;DR

This paper explores the potential of using an x-ray free-electron laser to detect vacuum birefringence, proposing an experimental setup where the laser interacts with itself to produce measurable polarization changes.

Contribution

It introduces a novel XFEL-based experimental scheme for measuring vacuum birefringence, highlighting its feasibility and potential advantages over optical laser methods.

Findings

XFEL alone can potentially detect vacuum birefringence.

The proposed scheme's effectiveness depends on specific x-ray optical parameters.

Idealized scenarios show comparable discovery potential to optical laser experiments.

Abstract

We study the perspectives of measuring the phenomenon of vacuum birefringence predicted by quantum electrodynamics using an x-ray free-electron laser (XFEL) alone. We devise an experimental scheme allowing the XFEL beam to collide with itself under a finite angle, and thus act as both pump and probe field for the effect. The signature of vacuum birefringence is encoded in polarization-flipped signal photons to be detected with high-purity x-ray polarimetry. Our findings for idealized scenarios underline that the discovery potential of solely XFEL-based setups can be comparable to those involving optical high-intensity lasers. For currently achievable scenarios, we identify several key details of the x-ray optical ingredients that exert a strong influence on the magnitude of the desired signatures.