# The semi-classical limit with delta potentials

## TL;DR

This paper analyzes the semi-classical limit of quantum evolution with delta potentials, showing it can be approximated by a modified classical evolution away from collision times, with explicit error bounds.

## Contribution

It introduces a novel approximation of quantum dynamics with delta potentials by a self-adjoint extension of classical generators, capturing the semi-classical behavior near singular interactions.

## Key findings

- Quantum evolution approximated by classical dynamics with explicit error bounds
- Approximation valid away from collision times
- Extension of classical generator accounts for delta potential effects

## Abstract

We consider the semi-classical limit of the quantum evolution of Gaussian coherent states whenever the Hamiltonian $\mathsf H$ is given, as sum of quadratic forms, by $\mathsf H= -\frac{\hbar^{2}}{2m}\,\frac{d^{2}\,}{dx^{2}}\,\dot{+}\,\alpha\delta_{0}$, with $\alpha\in\mathbb R$ and $\delta_{0}$ the Dirac delta-distribution at $x=0$. We show that the quantum evolution can be approximated, uniformly for any time away from the collision time and with an error of order $\hbar^{3/2-\lambda}$, $0\!<\!\lambda\!<\!3/2$, by the quasi-classical evolution generated by a self-adjoint extension of the restriction to $\mathcal C^{\infty}_{c}({\mathscr M}_{0})$, ${\mathscr M}_{0}:=\{(q,p)\!\in\!\mathbb R^{2}\,|\,q\!\not=\!0\}$, of ($-i$ times) the generator of the free classical dynamics; such a self-adjoint extension does not correspond to the classical dynamics describing the complete reflection due to the infinite barrier. Similar approximation results are also provided for the wave and scattering operators.