Experimental evidence for Wigner's tunneling time

TL;DR

This study combines experimental and theoretical approaches to investigate electron tunneling time in strong-field ionization, providing evidence for a non-zero tunneling time delay and momentum, advancing understanding of quantum tunneling dynamics.

Contribution

It demonstrates the validity of the Wigner tunneling time treatment in strong-field ionization and reveals corrections to classical models through precise differential measurements.

Findings

Confirmation of non-zero tunneling time delay

Detection of non-vanishing longitudinal momentum

Validation of Wigner's quantum mechanical tunneling description

Abstract

Tunneling of a particle through a potential barrier remains one of the most remarkable quantum phenomena. Owing to advances in laser technology, electric fields comparable to those electrons experience in atoms are readily generated and open opportunities to dynamically investigate the process of electron tunneling through the potential barrier formed by the superposition of both laser and atomic fields. Attosecond-time and angstrom-space resolution of the strong laser-field technique allow to address fundamental questions related to tunneling, which are still open and debated: Which time is spent under the barrier and what momentum is picked up by the particle in the meantime? In this combined experimental and theoretical study we demonstrate that for strong-field ionization the leading quantum mechanical Wigner treatment for the time resolved description of tunneling is valid. We achieve a high sensitivity on the tunneling barrier and unambiguously isolate its effects by performing a differential study of two systems with almost identical tunneling geometry. Moreover, working with a low frequency laser, we essentially limit the non-adiabaticity of the process as a major source of uncertainty. The agreement between experiment and theory implies two substantial corrections with respect to the widely employed quasiclassical treatment: In addition to a non-vanishing longitudinal momentum along the laser field-direction we provide clear evidence for a non-zero tunneling time delay. This addresses also the fundamental question how the transition occurs from the tunnel barrier to free space classical evolution of the ejected electron.