Witnessing Quantum Entanglement Using Resonant Inelastic X-ray Scattering

TL;DR

This paper introduces a novel method to detect quantum entanglement in materials using resonant inelastic x-ray scattering, expanding entanglement measurement tools beyond traditional Hermitian operator techniques.

Contribution

The authors develop a way to extract quantum Fisher information from non-Hermitian operators and formulate an entanglement witness specifically for RIXS, enabling direct entanglement detection in quantum materials.

Findings

Entanglement can be detected in iridate dimers using RIXS when symmetry considerations are included.

The method accounts for x-ray polarization and photon energy effects on entanglement detection.

Application to Ba3CeIr2O9 shows direct evidence of orbital entanglement between Ir sites.

Abstract

Although entanglement is both a central ingredient in our understanding of quantum many-body systems and an essential resource for quantum technologies, we only have a limited ability to quantify entanglement in real quantum materials. Thus far, entanglement metrology in quantum materials has been limited to measurements involving Hermitian operators, such as the detection of spin entanglement using inelastic neutron scattering. Here, we devise a method to extract the quantum Fisher information (QFI) from non-Hermitian operators and formulate an entanglement witness for resonant inelastic x-ray scattering (RIXS). Our approach is then applied to the model iridate dimer system Ba$_3$CeIr$_2$O$_9$ and used to directly test for entanglement of the electronic orbitals between neighboring Ir sites. We find the entanglement can be detected if we account for the expected symmetries, parity, and electron number conservation, of the dimer system. We also consider the roles that the incident and outgoing x-ray polarizations and the incident photon energy play in entanglement detection. Our protocol provides a new handle for entanglement detection in quantum materials.