Conditional global entanglement in a Kosterlitz-Thouless quantum phase transition

Entanglement is known as an important indicator for characterizing different types of quantum phase transitions (QPTs); however, it faces some challenges in the Kosterlitz-Thouless (KT) phase transitions due to an essential singularity which cannot be identified in finite derivatives of the ground-state energy. In this paper, we consider global entanglement (GE) in a KT phase transition and show that while it does not indicate any clear signature of the phase transition, the conditional version of GE is a good indicator with strong signatures of the KT transition. In particular, we study a deformed version of the Zd Kitaev model which has an intermediate KT phase which separates a Zd topological phase from a magnetized phase at two different KT transition points. Using a mapping to the classical d-state clock model, we consider GE and the generalized GE and show that they do not provide a reliable indicator of transition points. However, their difference, called conditional global entanglement (Q), shows a peak at the first KT transition point. Additionally, we show that it can characterize various phases of the model as it behaves substantially differently in each phase. We therefore conclude that Q is a useful measure that can characterize various phases of KT QPTs as well as their related critical points.

Automated summary

This paper investigates the global entanglement (GE) and conditional global entanglement (Q) in Kosterlitz-Thouless (KT) phase transitions. It finds that while GE does not indicate clear transition points, Q shows strong signatures of the KT transition points. The study also demonstrates that Q can characterize various phases of the model and behaves differently in each phase.