Maximum population transfer in a periodically driven two-level system

TL;DR

This paper investigates optimal population transfer in a driven two-level quantum system, providing analytical approximations and applications to control protocols in complex molecular models.

Contribution

It introduces a simple analytical model for population transfer in a periodically driven two-level system, applicable to multi-level systems at avoided crossings.

Findings

Optimal population transfer occurs through fixed-duration steps.

Analytical expressions approximate the evolution operator at all times.

Model applicable to control protocols in complex molecular systems.

Abstract

We study the dynamics of a two-level quantum system under the influence of sinusoidal driving in the intermediate frequency regime. Analyzing the Floquet quasienergy spectrum, we find combinations of the field parameters for which population transfer is optimal and takes place through a series of well defined steps of fixed duration. We also show how the corresponding evolution operator can be approximated at all times by a very simple analytical expression. We propose this model as being specially suitable for treating periodic driving at avoided crossings found in complex multi-level systems, and thus show a relevant application of our results to designing a control protocol in a realistic molecular model