2025/12/03 by Ryan Larson, Larson, Ryan, Rubem Mondaini +3 · 1 citation
Physics and Astronomy · Materials Science · #Physics of Superconductivity and Magnetism #Quantum many-body systems #Iron-based superconductors research
paper · pdf · doi:10.48550/arxiv.2512.04056
Quantum simulations are a powerful tool for exploring strongly correlated many-body phenomena. Yet, their reach is limited by the fermion sign problem, which causes configuration weights to become negative, compromising statistical sampling. In auxiliary-field Quantum Monte Carlo calculations of the doped Hubbard model, neglecting the sign \cal S of the weight leads to qualitatively wrong results -- most notably, an apparent suppression rather than enhancement of d-wave pairing at low temperature. Here we approach the problem from a different perspective: instead of identifying negative-weight paths, we examine the statistics of measured observables in a sign-resolved manner. By analyzing histograms of key quantities (kinetic energy, antiferromagnetic structure factor, and pair susceptibilities) for configurations with \cal S=±1, we derive an exact relation linking the bias from ignoring the sign to the difference between sign-resolved means, Δμ, and the average sign, ⟨ \cal S⟩. Our framework provides a precise diagnostic of the origin of measurement bias in Quantum Monte Carlo and clarifies why observables such as the d-wave susceptibility are especially sensitive to the sign problem.