Landau-Zener Formula in a "Non-Adiabatic" regime for avoided crossings

TL;DR

This paper explores the Landau-Zener transition probability in a non-adiabatic regime for avoided crossings, extending the classical formula using microlocal analysis and the WKB method.

Contribution

It generalizes the Landau-Zener formula to a non-adiabatic regime where the interaction parameter dominates, using microlocal branching models and asymptotic analysis.

Findings

Derived asymptotic expansions of local transfer matrices.

Extended the Landau-Zener formula to a new parameter regime.

Provided a microlocal analysis framework for non-adiabatic transitions.

Abstract

We study a two-level transition probability for a finite number of avoided crossings with a small interaction. Landau-Zener formula, which gives the transition probability for one avoided crossing as $e^{-\pi\frac{\varepsilon^{2}}{h}}$, implies that the parameter $h$ and the interaction $\varepsilon$ play an opposite role when both tend to $0$. The exact WKB method produces a generalization of that formula under the optimal regime $\frac{h}{\varepsilon^2}$ tends to~0. In this paper, we investigate the case $\frac{\varepsilon^2}{h}$ tends to 0, called "non-adiabatic" regime. This is done by reducing the associated Hamiltonian to a microlocal branching model which gives us the asymptotic expansions of the local transfer matrices.