Entanglement dynamics in collision models and entanglement quilts

TL;DR

This paper analyzes entanglement dynamics in quantum collision models, introducing a diagrammatic method and identifying a novel multipartite entanglement structure called 'entanglement quilt' that is highly sensitive to local excitations.

Contribution

It presents an analytical approach to entanglement evolution in collision models and introduces the concept of entanglement quilts, a new form of genuine multipartite entanglement.

Findings

Entanglement quilts involve every qubit being entangled with all others.

Local excitations can destroy entanglement quilts.

Conservation of squared concurrence aids in understanding entanglement propagation.

Abstract

We study the entanglement dynamics of a family of quantum collision models by analytically solving the pairwise concurrence for all qubit pairs. We introduce a diagrammatic method that offers an intuitive, frame-by-frame understanding of these dynamics. This allows us to monitor how a single collision affects the entanglement of the whole many-body system in some special cases. We focus on a class of models where the square of concurrence is a conserved quantity in the qubit collisions, aiding us to formulate general rules of entanglement propagation. In particular, among the multiple examples we will be showing, we identify a type of genuine multipartite entanglement, which we refer to as \textit{entanglement quilt}, where every qubit is entangled with every other qubit. We find that in some models, an entanglement quilt is hypersensitive to local excitation fluctuations: The presence of even a single excited qubit can destroy the entanglement quilts. We offer a detailed mathematical treatment on the phenomena, which can help us understand the disappearance of long-range entanglement in condensed matter systems above zero temperature. We also speculate about a possible property of the entanglement quilt: Every subsystem of it is entangled with every other subsystem.