Quantum versus classical chirps in a Rydberg atom

TL;DR

This paper compares quantum and classical excitation mechanisms in a Rydberg atom under chirped driving, highlighting how different resonant processes dominate depending on system parameters.

Contribution

It introduces a detailed analysis of quantum and classical resonances in a Rydberg atom, using approximations to distinguish regimes of excitation.

Findings

Identification of ladder climbing and autoresonance as key excitation mechanisms.

Characterization of persistent 1:1 and 2:1 resonances in parameter space.

Demonstration of regimes where quantum or classical descriptions are more appropriate.

Abstract

The interplay between quantum-mechanical and classical evolutions in a chirped driven Rydberg atom is discussed. It is shown that the system allows two continuing resonant excitation mechanisms, i.e., a successive two-level transitions (ladder climbing) and a continuing classical-like nonlinear phase locking (autoresonance). The persistent $1:1$ and $2:1$ resonances between the driving and the Keplerian frequencies are studied in detail and characterized in terms of two dimensionless parameters $P_{1,2}$ representing the driving strength and the nonlinearity in the problem, respectively. The quantum-mechanical rotating wave and the classical single resonance approximations are used to describe the regimes of efficient classical or quantum-mechanical excitation in this two-parameter space.