Floquet exceptional contours in Lindblad dynamics with time-periodic drive and dissipation

TL;DR

This paper investigates how periodic driving in Lindblad systems creates exceptional point contours, revealing new structures in the transient dynamics and offering a novel approach to accessing quantum exceptional points.

Contribution

It introduces Floquet analysis of Lindblad dynamics with periodic drive, uncovering exceptional point contours and complex structures in the parameter space.

Findings

Periodic modulations generate exceptional point lines at low dissipator strengths.

Rich exceptional point structures emerge in parameter space due to Floquet driving.

Extending Lindblad Liouvillians to Floquet domain offers a new route to quantum exceptional points.

Abstract

The dynamics of an isolated quantum system is coherent and unitary. Weak coupling to the environment leads to decoherence, which is traditionally modeled with a Lindblad equation for the system's density matrix. Starting from a pure state, such a system approaches a steady state (mixed or otherwise) in an underdamped or overdamped manner. This transition occurs at an eigenvalue degeneracy of a Lindblad superoperator, called an exceptional point (EP), where corresponding eigenvectors coalesce. Recent years have seen an explosion of interest in creating exceptional points in a truly quantum domain, driven by the enhanced sensitivity and topological features EPs have shown in their classical realizations. Here, we present Floquet analysis of a prototypical qubit whose drive or dissipator strengths are varied periodically. We consider models with a single dissipator that generate global loss (phase damping) or mode-selective loss (spontaneous emission). In all cases, we find that periodic modulations lead to EP lines at small dissipator strengths, and a rich EP structure in the parameter space. Our analytical and numerical results show that extending Lindblad Liouvillians to the Floquet domain is a new, potentially preferred route to accessing exceptional points in the transient dynamics towards the Lindblad steady state.