Abstract

Modern semiconductor technology has enabled the fabrication of solid-state analogues of one-dimensional atoms. These are electrons confined in quantum wells by a graded band gap. Such structures typically have energy level spacings between 1 and 100 meV, and depths up to 300 meV. The development of a free-electron laser that is tuneable between 0.5 and 20 meV has now made possible the study of such solid-state atoms in oscillating electromagnetic fields with amplitudes sufficient to ionize them at frequencies much smaller than their binding energies. Thus experiments analogous to those carried out on atoms in strong electromagnetic fields can be performed (for example, ionization, harmonic generation). This chapter first introduces the physics of quantum wells, then discusses preliminary experimental results on ionization and harmonic generation from electrons in quantum wells, and finally describes the results of recent computer simulations. The chapter concludes by discussing a number of new issues in the interaction of light with matter which are raised in the study of solid-state atoms.

Introduction

Much of the theoretical work on quantum chaos in periodically-driven systems has been motivated by classic experiments on the microwave ionization in hydrogen. In these experiments, Rydberg hydrogen atoms are driven by microwaves with photon energy hv ≪ ionization energy E1 of the Rydberg atom, and with electric field energies comparable to E1. For hv smaller than the separation between Rydberg levels (scaled frequency < 1), simple classical models predict remarkably well observed ionization thresholds. Ionization is associated with the destruction of classical invariant tori and the onset of global chaotic diffusion.