Coherent control of an Helium-Ion ensemble

TL;DR

This study demonstrates how to control coherence loss in helium ionization using ab initio simulations, revealing how to reconstruct original ion coherences through delay-dependent electric dipole measurements.

Contribution

It introduces a method to control and reconstruct ion coherence in helium using pump-probe simulations and fine-structure effects, advancing attosecond photoemission understanding.

Findings

Coherence between helium ion states can be controlled and reconstructed.

Delay-dependent electric dipole reveals original ion coherences.

Fine-structure splitting enables probing relativistic effects.

Abstract

Attosecond pulses can ionize atoms in a coherent process. Since the emerging fragments are entangled, however, each preserves only a fraction of the initial coherence, thus limiting the chance of guiding the ion subsequent evolution. In this work, we use \emph{ab initio} simulations of pump-probe ionization of helium above the $2s/2p$ threshold to demonstrate how this loss of coherence can be controlled. Thanks to the participation of $2\ell n\ell'$ states, coherence between the ionic $2s$ and $2p$ states, which are degenerate in the non-relativistic limit, results in a stationary, delay-dependent electric dipole. From the picosecond real-time beating of the dipole, caused by the fine-structure splitting of the $n=2$ manifold, it is possible to reconstruct all original ion coherences, including between antiparallel-spin states, which are sensitive probe of relativistic effects in attosecond photoemission.