  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.
