Ultrafast resolution of tunneling delay time

Alexandra S Landsman,Ursula Keller,Robert Boge,Matthias Weger,Lukas Gallmann,Jochen Maurer,Claudio Cirelli,André Ludwig,Sebastian Heuser

doi:10.1364/optica.1.000343

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.

Highlights

Main Text: The question of how long a tunneling particle spends inside the barrier region has remained unresolved since the early days of quantum mechanics [1]
Common reactions in the broader scientific community to the tunneling time problem can be roughly grouped into two categories: 1) “it’s easy” or 2) “it can’t be done”
It is sometimes suggested that the tunneling time is instantaneous because both the Keldysh [11] and the closely related Buttiker-Landauer [2] times are imaginary

Summary

Introduction

The question of how long a tunneling particle spends inside the barrier region has remained unresolved since the early days of quantum mechanics [1]. Of the five theoretical approaches considered, two cannot be excluded by our measurements: the Larmor time and the probability distribution of tunneling times constructed using FPIs. These two are not mutually exclusive.

Results

Conclusion