Measuring the quantum state of photoelectrons

TL;DR

This paper employs quantum state tomography to fully characterize photoelectrons emitted from helium and argon, revealing quantum entanglement effects and providing new insights into light-induced electronic processes.

Contribution

It demonstrates the use of quantum state tomography to analyze photoelectrons, highlighting entanglement effects in argon and advancing quantum spectroscopy methods.

Findings

Helium photoelectrons are in a pure quantum state.

Argon photoelectrons exhibit entanglement with the ion.

State tomography reveals quantum properties of photoelectrons.

Abstract

A photoelectron, emitted due to the absorption of light quanta as described by the photoelectric effect, is often characterized experimentally by a classical quantity, its momentum. However, since the photoelectron is a quantum object, its rigorous characterization requires the reconstruction of the complete quantum state, the photoelectron's density matrix. Here, we use quantum state tomography to fully characterize photoelectrons emitted from helium and argon atoms upon absorption of ultrashort, extreme ultraviolet light pulses. While in helium we measure a pure photoelectronic state, in argon, spin-orbit interaction induces entanglement between the ion and the photoelectron, leading to a reduced purity of the photoelectron state. Our work shows how state tomography gives new insights into the fundamental quantum aspects of light-induced electronic processes in matter, bridging the fields of photoelectron spectroscopy and quantum information, and offering new spectroscopic possibilities for quantum technology.