Abstract
Despite its fully unitary dynamics, the bosonic Kitaev chain (BKC) displays key hallmarks of non-Hermitian physics, including nonreciprocal transport and the non-Hermitian skin effect. Here, we demonstrate another remarkable phenomena: the existence of an entanglement phase transition (EPT) in a variant of the BKC that occurs as a function of a Hamiltonian parameter and which coincides with a transition from a reciprocal to a nonreciprocal phase. As is reduced below a critical value, the postquench entanglement entropy of a subsystem of size goes from a volume-law phase, where it scales as , to a supervolume-law phase, where it scales like , where is the total system size. This EPT occurs for a system undergoing purely unitary evolution and does not involve measurements, postselection, disorder, or dissipation. We derive analytically the entanglement entropy out of and at the critical point for the cases of and .
- Received 6 September 2023
- Accepted 20 December 2023
DOI:https://doi.org/10.1103/PRXQuantum.5.010313
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
Our work addresses two major topics of current interest. The first involves entanglement phase transitions (EPTs), where a physical model exhibits different scaling phases for its entanglement, thus allowing one to characterize condensed-matter systems using quantum information-theoretic properties. The second topic involves non-Hermitian systems. In such systems, effective nonunitary dynamics gives rise to surprising and exotic properties such as the non-Hermitian skin effect, which causes the system to localize at the edges. In both cases, measurement and postselection are thought to be essential in observing their most interesting properties.
Incorporating elements from both these fields in a nontrivial manner, our work realizes something that was previously thought to be impossible: the realization of a many-body EPT in a measurement-free system with a Hermitian Hamiltonian and purely unitary evolution. We study a modified version of the bosonic Kitaev chain, which is a bosonic model known to exhibit the non-Hermitian skin effect despite only undergoing unitary evolution. By tuning a real-space hopping parameter g in this model, we can tune it between a reciprocal and nonreciprocal phase. Our main result is to show that this model then exhibits an EPT between a supervolume-law and a volume-law phase, where the entanglement either scales quadratically or linearly in total system size. The identification of a closed system exhibiting different entanglement phases represents a significant departure from any previous work on the topic and demonstrates that effective closed-system non-Hermitian dynamics in bosonic systems can inherit many of the interesting properties studied in the field of non-Hermitian physics.
Since the phenomena we describe require no postselection or measurement whatsoever, this reduces exponentially the experimental overhead in observing an EPT. We also shed light on the relationship between nonreciprocity and entanglement, an emerging topic that deserves further study.
