Probing Phases and Quantum Criticality using Deviations from the Local Fluctuation-Dissipation Theorem

TL;DR

This paper introduces a novel method to determine the finite temperature phase diagram of quantum Hamiltonians using deviations from the local fluctuation-dissipation theorem, enabling experimental identification of quantum phases and criticality without extensive simulations.

Contribution

The authors propose a new experimental approach that leverages local observables and the fluctuation-dissipation theorem to map quantum phase diagrams directly from in situ measurements.

Findings

Successfully tested with quantum Monte Carlo simulations of the 2D Bose Hubbard model.

Demonstrated ability to identify quantum phases and critical regions from local measurements.

Extended fluctuation-dissipation theorem utility from thermometry to phase identification.

Abstract

Introduction Cold atomic gases in optical lattices are emerging as excellent laboratories for testing models of strongly interacting particles in condensed matter physics. Currently, one of the major open questions is how to obtain the finite temperature phase diagram of a given quantum Hamiltonian directly from experiments. Previous work in this direction required quantum Monte Carlo simulations to directly model the experimental situation in order to extract quantitative information, clearly defeating the purpose of an optical lattice emulator. Here we propose a new method that utilizes deviations from a local fluctuation dissipation theorem to construct a finite temperature phase diagram, for the first time, from local observables accessible by in situ experimental observations. Our approach extends the utility of the fluctuation-dissipation theorem from thermometry to the identification of quantum phases, associated energy scales and the quantum critical region. We test our ideas using state-of-the-art large-scale quantum Monte Carlo simulations of the two-dimensional Bose Hubbard model.