Quantum Dissipation at Conical Intersections of Quasienergies

TL;DR

This paper explores how Floquet states behave near conical intersections of quasienergies in driven quantum systems, revealing symmetry effects on dissipation, population dynamics, and the emergence of maximally mixed states at high frequencies.

Contribution

It provides new analytical and numerical insights into the effects of symmetries and dissipation on Floquet states near quasienergy intersections in driven two-level systems.

Findings

Mean energies interchange on constant quasienergy manifolds.

Stationary populations reflect mean energy behavior under dissipation.

High-frequency driving leads to maximally mixed states with high entropy.

Abstract

We investigate the properties of Floquet states in the vicinity of a conical intersection of quasienergies and work out the consequences of the underlying spatio-temporal symmetries for a driven two-level system coupled to an ohmic heat bath. We find that on manifolds with constant quasienergy splitting, the mean energies of the Floquet states are continuously interchanged. In the presence of dissipation, the parameter dependence of the stationary populations generally resembles that of the mean energies. In turn, the mean energies are an indicator for the qualitative behavior of the density operator in the long-time limit. A further consequence of the symmetries is that for specific driving parameters, the stationary state may be fully mixed even at arbitrarily low temperatures. For large driving frequencies, such states with maximal entropy are found in the whole vicinity of the intersection, which can be explained by a chirality emerging in this limit. Analytical results beyond a high-frequency approximation are illustrated by numerical data.