Quantum entanglement in strong-field ionization

TL;DR

This paper introduces a novel method to quantify quantum entanglement between an electron and its parent ion during strong-field ionization, revealing complex dynamics influenced by laser parameters and ionization regimes.

Contribution

It proposes an approximate entanglement entropy measure using reduced density matrices for complex systems, enabling analysis of entanglement evolution in strong-field ionization.

Findings

Entanglement dynamics depend on laser parameters and ionization regime.

Entanglement decreases over time in the over-the-barrier ionization regime.

The method captures entanglement evolution beyond simple models.

Abstract

We investigate the time-evolution of quantum entanglement between an electron, liberated by a strong few-cycle laser pulse, and its parent ion-core. Since the standard procedure is numerically prohibitive in this case, we propose a novel way to quantify the quantum correlation in such a system: we use the reduced density matrices of the directional subspaces along the polarization of the laser pulse and along the transverse directions as building blocks for an approximate entanglement entropy. We present our results, based on accurate numerical simulations, in terms of several of these entropies, for selected values of the peak electric field strength and the carrier-envelope phase difference of the laser pulse. The time evolution of the mutual entropy of the electron and the ion-core motion along the direction of the laser polarization is similar to our earlier results based on a simple one-dimensional model. However, taking into account also the dynamics perpendicular to the laser polarization reveals a surprisingly different entanglement dynamics above the laser intensity range corresponding to pure tunneling: the quantum entanglement decreases with time in the over-the-barrier ionization regime.