Abstract
Recent years have seen remarkable development in open quantum systems effectively described by non-Hermitian Hamiltonians. A unique feature of non-Hermitian topological systems is the skin effect, anomalous localization of an extensive number of eigenstates driven by nonreciprocal dissipation. Despite its significance for non-Hermitian topological phases, the relevance of the skin effect to quantum entanglement and critical phenomena has remained unclear. Here, we find that the skin effect induces a nonequilibrium quantum phase transition in the entanglement dynamics. We show that the skin effect gives rise to a macroscopic flow of particles and suppresses the entanglement propagation and thermalization, leading to the area law of the entanglement entropy in the nonequilibrium steady state. Moreover, we reveal an entanglement phase transition induced by the competition between the unitary dynamics and the skin effect even without disorder or interactions. This entanglement phase transition accompanies nonequilibrium quantum criticality characterized by a nonunitary conformal field theory whose effective central charge is extremely sensitive to the boundary conditions. We also demonstrate that it originates from an exceptional point of the non-Hermitian Hamiltonian and the concomitant scale invariance of the skin modes localized according to the power law. Furthermore, we show that the skin effect leads to the purification and the reduction of von Neumann entropy even in Markovian open quantum systems described by the Lindblad master equation. Our work opens a way to control the entanglement growth and establishes a fundamental understanding of phase transitions and critical phenomena in open quantum systems far from thermal equilibrium.
- Received 10 June 2022
- Revised 2 March 2023
- Accepted 13 March 2023
DOI:https://doi.org/10.1103/PhysRevX.13.021007
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Unique phenomena in quantum physics, including the power of quantum computers, arise from quantum entanglement, a type of correlation that has no analogs in classical physics. In quantum systems isolated from the external environment, entanglement extensively propagates in the dynamics. However, the nature of entanglement in open quantum systems—which exchange energy, particles, and information with the external environment—has remained elusive. Here, we find that the non-Hermitian skin effect, a macroscopic flow of particles and concomitant anomalous localization, plays an important role in the entanglement dynamics of open quantum systems.
We demonstrate that the skin effect suppresses the entanglement propagation and thermalization and even induces a new type of entanglement phase transition. We identify the origin of our dynamical phase transition as the scale invariance of the skin effect due to the interplay between coherent coupling and dissipation. We also show that this scale invariance is characterized by a new type of field theory that dramatically changes its behavior depending on whether a boundary is present or not.
Thanks to rapid advances in quantum simulations and technologies, the physics of open quantum systems has attracted growing interest. Our findings open a way to control the entanglement dynamics and provide a fundamental understanding of phase transitions and critical phenomena in open quantum systems far from thermal equilibrium.
