QI In the literature: contested

Is there a nonzero tunneling delay in strong-field ionization?

In plain words

An attoclock uses a rotating laser field, like the hand of a clock, to time when an electron escapes an atom by tunneling. Experiments and analyses disagree on whether the escape takes a finite time or none.

Precise statement

In elliptically polarized strong-field ionization of atomic hydrogen or helium, extract the tunneling delay $\tau_T$ from the photoelectron momentum offset angle after subtracting the Coulomb deflection computed from the full time-dependent Schrodinger equation, and decide whether $\tau_T = 0$ within resolution. A 2019 hydrogen experiment (Sainadh et al., Nature) reported tau_T below about $1.8e-18\,\mathrm{s}$.

What would settle it

Agreement between calibrated attoclock measurements on hydrogen at several intensities and a clock-model prediction.

Status in the literature

Unverified note

2025 analyses (e.g. arXiv:2503.07859) continue to compare attoclock and Larmor-clock interpretations of strong-field tunneling.