FOTOC complexity in an extended Lipkin-Meshkov-Glick model

TL;DR

This paper investigates the behavior of fidelity out-of-time-order correlators (FOTOCs) in an extended Lipkin-Meshkov-Glick model, revealing their distinctive features at quantum phase transitions and their relation to quantum complexity measures.

Contribution

It introduces the analysis of FOTOCs and their complexity in the extended Lipkin-Meshkov-Glick model, highlighting their behavior near quantum phase transitions and the divergence of the Ricci scalar.

Findings

FOTOC behavior differs in symmetric and broken-symmetry phases.

FOTOC rescaled with time matches Loschmidt echo at small times.

Ricci scalar diverges at phase transition in the broken-symmetry phase.

Abstract

We study fidelity out-of-time-order correlators (FOTOCs) in an extended Lipkin-Meshkov-Glick model and demonstrate that these exhibit distinctive behaviour at quantum phase transitions in both the ground and the excited states. We show that the dynamics of the FOTOC have different behaviour in the symmetric and broken-symmetry phases, and as one approaches phase transition. If we rescale the FOTOC operator with time, then for small times, we establish that it is identical to the Loschmidt echo. We also compute the Nielsen complexity of the FOTOC operator in both phases, and apply this operator on the ground and excited states to obtain the quasi-scrambled state of the model. The FOTOC operator introduces a small perturbation on the original ground and excited states. For this perturbed state, we compute the quantum information metric to first order in perturbation, in the thermodynamic limit. We find that the associated Ricci scalar diverges at the phase transition on the broken-symmetry phase side, in contrast to the zeroth order result. Finally, we comment upon the Fubini-Study complexity in this model.