Maximal quantum entanglement at exceptional points via unitary and thermal dynamics

TL;DR

This paper explores how combining unitary and thermal dynamics in open quantum systems can lead to maximal entanglement and entropy at exceptional points, revealing complex phase behavior and potential for quantum control.

Contribution

It introduces a novel protocol using periodic unitary and thermal dynamics to realize a rich phase diagram with exceptional points and demonstrates maximal entanglement and entropy at these points.

Findings

Maximal entanglement occurs at exceptional points controlled by Hermitian coupling.

Entropy of qubits is maximized at the exceptional points.

The protocol realizes a quantum Hatano-Nelson model with asymmetric tunneling.

Abstract

Minimal, open quantum systems that are governed by non-Hermitian Hamiltonians have been realized across multiple platforms in the past two years. Here we investigate the dynamics of open systems with Hermitian or anti-Hermitian Hamiltonians, both of which can be implemented in such platforms. For a single system subject to unitary and thermal dynamics in a periodic manner, we show that the corresponding Floquet Hamiltonian has a rich phase diagram with numerous exceptional-point (EP) degeneracy contours. This protocol can be used to realize a quantum Hatano-Nelson model that is characterized by asymmetric tunneling. For one unitary and one thermal qubit, we show that the concurrence is maximized at the EP that is controlled by the strength of Hermitian coupling between them. Surprisingly, the entropy of each qubit is also maximized at the EP. Our results point to the multifarious phenomenology of systems undergoing unitary and thermal dynamics.