A solvable model of the breakdown of the adiabatic approximation

Abstract

Let $L\geq0$ and $0<\varepsilon\ll1$. Consider the following time-dependent family of $1D$ Schr\"{o}dinger equations with scaled and translated harmonic oscillator potentials $ i\varepsilon\partial_t u_{\varepsilon}=-\tfrac12\partial_x^2u_{\varepsilon}+V(t,x)u_{\varepsilon}$, $u_{\varepsilon}(-L-1,x)=\pi^{-1/4}\exp(-x^2/2) $, where $ V(t,x)= (t+L)^2x^2/2$, $t<-L$, $ V(t,x)= 0$, $-L\leq t \leq L$, and $ V(t,x)=(t-L)^2x^2/2$, $t>L$. The initial value problem is explicitly solvable in terms of Bessel functions. Using the explicit solutions we show that the adiabatic theorem breaks down as $\varepsilon\to 0$. For the case $L=0$ complete results are obtained. The survival probability of the ground state $\pi^{-1/4}\exp(-x^2/2)$ at microscopic time $t=1/\varepsilon$ is $1/\sqrt{2}+O(\varepsilon)$. For $L>0$ the framework for further computations and preliminary results are given.