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Title: Does the Larmor tunneling time saturate for thick barriers?
Plain: The Hartman effect predicts that the tunneling delay stops growing as the barrier gets thicker, which would imply speeds above that of light. Cold-atom experiments that use an atom's spin as a built-in clock can now test this.
Precise: For cold atoms (e.g. 87Rb) tunneling through an optical barrier with an internal-state Larmor clock, measure the transmitted-atom Larmor times $\tau_y$ and $\tau_z$ versus barrier width $L$ in the opaque regime $\kappa L >> 1$, $\kappa = \sqrt{2 m (V_0 - E)} / \hbar$, and determine whether they saturate with $L$ as the Hartman effect predicts for the phase delay.
Settled by: A Larmor-clock measurement over a range of $L$ reaching $\kappa L$ of several, with transmission high enough to resolve the precession.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: open
Status note: Larmor times of about 0.6 ms were measured for rubidium atoms in 2020, and their decrease at lower incident energy was reported in 2021 (arXiv:2101.12309).
Posed since: 1962