Excitation of Small Quantum Systems by High-Frequency Fields

TL;DR

This paper investigates how high-frequency fields excite multi-level quantum systems with slowly varying densities of states, revealing universal quasi-resonances and deriving an effective equation for their amplitudes.

Contribution

It introduces a general approach to analyze such quantum systems, characterizes Floquet eigenstates across energy scales, and identifies universal quasi-resonances independent of system details.

Findings

Universal sharp quasi-resonances are found on small energy scales.

An effective tight-binding equation describes the amplitudes of quasi-resonances.

Two classes of systems are discussed with different non-universal behaviors.

Abstract

The excitation by a high frequency field of multi--level quantum systems with a slowly varying density of states is investigated. A general approach to study such systems is presented. The Floquet eigenstates are characterized on several energy scales. On a small scale, sharp universal quasi--resonances are found, whose shape is independent of the field parameters and the details of the system. On a larger scale an effective tight--binding equation is constructed for the amplitudes of these quasi--resonances. This equation is non--universal; two classes of examples are discussed in detail.