A perfect X-ray beam splitter and its applications to time-domain interferometry and quantum optics exploiting free-electron lasers

TL;DR

This paper introduces a novel method to generate phase-locked, ultrashort X-ray pulse sequences using free-electron lasers by splitting the electron bunch before photon emission, enabling advanced time-domain interferometry and quantum optics experiments.

Contribution

The paper presents a new FEL mode that splits the electron bunch prior to photon generation, achieving phase-locked X-ray pulses with sub-femtosecond duration, which was not previously possible.

Findings

Enables phase-locked X-ray pulse sequences for interferometry

Allows classical and quantum optics experiments with X-rays

Facilitates damage-free measurements and spectroscopy

Abstract

X-ray free-electron lasers (FEL) deliver ultrabright X-ray pulses, but not the sequences of phase-coherent pulses required for time-domain interferometry and control of quantum states. For conventional split-and-delay schemes to produce such sequences the challenge stems from extreme stability requirements when splitting Angstrom wavelength beams where tiniest path length differences introduce phase jitter. We describe an FEL mode based on selective electron bunch degradation and transverse beam shaping in the accelerator, combined with a self-seeded photon emission scheme. Instead of splitting the photon pulses after their generation by the FEL, we split the electron bunch in the accelerator, prior to photon generation, to obtain phase-locked X-ray pulses with sub-femtosecond duration. Time-domain interferometry becomes possible, enabling the concomitant program of classical and quantum optics experiments with X-rays. The scheme leads to new scientific benefits of cutting-edge FELs with attosecond and/or high-repetition rate capabilities, ranging from the X-ray analog of Fourier transform infrared spectroscopy to damage-free measurements.