Entanglement phase transition due to reciprocity breaking without measurement or post-selection

TL;DR

This paper uncovers an entanglement phase transition in a bosonic Kitaev chain variant, driven by reciprocity breaking, occurring under purely unitary evolution without measurements or dissipation, with analytical insights at the critical point.

Contribution

It demonstrates a novel entanglement phase transition linked to reciprocity breaking in a unitary system, without involving measurement or dissipation, and provides analytical results at the critical point.

Findings

Entanglement entropy transitions from volume-law to super-volume law as g decreases.

Transition coincides with a shift from reciprocal to non-reciprocal phase.

Analytical expressions derived for entanglement entropy at criticality.

Abstract

Despite its fully unitary dynamics, the bosonic Kitaev chain (BKC) displays key hallmarks of non-Hermitian physics including non-reciprocal 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 g, and which coincides with a transition from a reciprocal to a non-reciprocal phase. As g is reduced below a critical value, the post-quench entanglement entropy of a subsystem of size l goes from a volume-law phase where it scales as l to a super-volume law phase where it scales like lN with N the total system size. This EPT occurs for a system undergoing purely unitary evolution and does not involve measurements, post-selection, disorder or dissipation. We derive analytically the entanglement entropy out of and at the critical point for the $l=1$ and $l/N \ll 1$ case.