Generation of entanglement using a short-wavelength seeded free-electron laser

Quantum entanglement between the degrees of freedom encountered in the classical world is challenging to observe due to the surrounding environment. To elucidate this issue, a team of scientists including Michael Meyer, Leading Scientist and Group Head of SQS investigate the entanglement generated over ultrafast timescales in a bipartite quantum system comprising two massive particles: a free-moving photoelectron, which expands to a mesoscopic length scale, and a light-dressed atomic ion, which represents a hybrid state of light and matter.

Although the photoelectron spectra are measured classically, the entanglement allows revealing information about the dressed-state dynamics of the ion and the femtosecond extreme ultraviolet pulses delivered by a seeded free-electron laser. The observed generation of entanglement is interpreted using the time-dependent von Neumann entropy. The results unveil the potential for using short-wavelength coherent light pulses from free-electron lasers to generate entangled photoelectron and ion systems for studying “spooky” action at a distance.

The study was led by Saikat Nandi from the Institut Lumière Matière, CNRS in Lyon. Read more: https://www.science.org/doi/10.1126/sciadv.ado0668