Quantum Phase Transitions and Localization in Semigroup Fredkin Spin Chain

TL;DR

This paper introduces an extended Fredkin spin chain model with new degrees of freedom, revealing multiple phases, quantum phase transitions, and localized excited states without disorder, highlighting rich quantum critical phenomena.

Contribution

The paper constructs a novel extended quantum spin chain model incorporating arrow indices linked to semigroup structures, revealing new phases and localization phenomena.

Findings

Ground states form three distinct phases with different entanglement properties.

Quantum phase transitions occur at phase boundaries.

Localized excited states arise without disorder due to disconnections in arrow indices.

Abstract

We construct an extended quantum spin chain model by introducing new degrees of freedom to the Fredkin spin chain. The new degrees of freedom called arrow indices are partly associated to the symmetric inverse semigroup $\cS^3_1$. Ground states of the model fall into three different phases, and quantum phase transition takes place at each phase boundary. One of the phases exhibits logarithmic violation of the area law of entanglement entropy and quantum criticality, whereas the other two obey the area law. As an interesting feature arising by the extension, there are excited states due to disconnections with respect to the arrow indices. We show that these states are localized without disorder.