Tunneling Time in Ultrafast Science is Real and Probabilistic

TL;DR

This study confirms that tunneling time in ultrafast laser ionization is real and probabilistic, challenging traditional instantaneous models, and highlights the importance of accounting for uncertainty in electron dynamics reconstruction.

Contribution

It provides experimental evidence supporting a probabilistic tunneling time distribution and compares theoretical models against precise measurements in strong laser fields.

Findings

Refined measurements show a real tunneling delay time.

Only Larmor time and Feynman Path Integral models align with data.

FPI predicts a broad, long-tailed tunneling time distribution.

Abstract

We compare the main competing theories of tunneling time against experimental measurements using the attoclock in strong laser field ionization of helium atoms. Refined attoclock measurements reveal a real and not instantaneous tunneling delay time over a large intensity regime, using two different experimental apparatus. Only two of the theoretical predictions are compatible within our experimental error: the Larmor time, and the probability distribution of tunneling times constructed using a Feynman Path Integral (FPI) formulation. The latter better matches the observed qualitative change in tunneling time over a wide intensity range, and predicts a broad tunneling time distribution with a long tail. The implication of such a probability distribution of tunneling times, as opposed to a distinct tunneling time, challenges how valence electron dynamics are currently reconstructed in attosecond science. It means that one must account for a significant uncertainty as to when the hole dynamics begin to evolve.