Dynamical phase transitions at finite temperature from fidelity and interferometric Loschmidt echo induced metrics

TL;DR

This paper investigates finite-temperature dynamical quantum phase transitions using fidelity and interferometric Loschmidt Echo metrics, revealing different behaviors and sensitivities, with applications to topological insulators.

Contribution

It introduces a comparative analysis of fidelity and interferometric Loschmidt Echo metrics at finite temperature, deriving analytic expressions and exploring their physical differences.

Findings

Fidelity LE shows gradual washing out of zero-temperature DQPTs with temperature.

Interferometric LE exhibits finite-temperature phase transitions.

Interferometric LE is more sensitive for microscopic quantum systems, fidelity LE is better for macroscopic many-body systems.

Abstract

We study finite-temperature Dynamical Quantum Phase Transitions (DQPTs) by means of the fidelity and the interferometric Loschmidt Echo (LE) induced metrics. We analyse the associated dynamical susceptibilities (Riemannian metrics), and derive analytic expressions for the case of two-band Hamiltonians. At zero temperature the two quantities are identical, nevertheless, at finite temperatures they behave very differently. Using the fidelity LE, the zero temperature DQPTs are gradually washed away with temperature, while the interferometric counterpart exhibits finite-temperature Phase Transitions (PTs). We analyse the physical differences between the two finite-temperature LE generalisations, and argue that, while the interferometric one is more sensitive and can therefore provide more information when applied to genuine quantum (microscopic) systems, when analysing many-body macroscopic systems, the fidelity-based counterpart is a more suitable quantity to study. Finally, we apply the previous results to two representative models of topological insulators in 1D and 2D.