Dynamic structure factor of superfluid He-4 from Quantum Monte Carlo: Maximum Entropy revisited

TL;DR

This paper revisits the use of the Maximum Entropy Method to extract the dynamic structure factor of superfluid helium-4 from Quantum Monte Carlo data, demonstrating that sharp spectral features can be reliably reconstructed with sufficient data accuracy.

Contribution

It introduces an improved MaxEnt procedure that preserves sharp spectral features in QMC data, challenging previous assumptions about entropic smoothing.

Findings

Sharp features are not washed out with accurate QMC data.

Spurious features are suppressed compared to chi-square minimization.

The method enhances spectral resolution in superfluid helium-4 analysis.

Abstract

We use the Maximum Entropy Method (MaxEnt) to estimate the dynamic structure factor of superfluid He-4 at T=1 K, by inverting imaginary-time density correlation functions computed by a Quantum Monte Carlo (QMC) simulation. Our procedure consists of a Metropolis random walk in the space of all possible spectral images, sampled from a probability density which includes the entropic prior, in the context of the so-called "classic" MaxEnt. Comparison with recent work by other authors shows that, contrary to what is often stated, sharp features in the reconstructed image are not "washed out" by the entropic prior if the underlying QMC data have sufficient accuracy. Only spurious features that tend to appear in a straightforward chi-square minimization are suppressed.