Quantum Monte Carlo simulations provide one of the more powerful and
versatile numerical approaches to condensed matter systems. However,
their application to frustrated quantum spin models, in all relevant
temperature regimes, is hamstrung by the infamous “sign problem.” Here
we exploit the fact that the sign problem is basis-dependent. Recent
studies have shown that passing to a dimer (two-site) basis eliminates
the sign problem completely for a fully frustrated spin model on the
two-leg ladder. We generalize this result to all partially frustrated
two-leg spin-1/2 ladders, meaning those where the diagonal and leg
couplings take any antiferromagnetic values. We find that, although the
sign problem does reappear, it remains remarkably mild throughout the
entire phase diagram. We explain this result and apply it to perform
efficient quantum Monte Carlo simulations of frustrated ladders,
obtaining accurate results for thermodynamic quantities such as the
magnetic specific heat and susceptibility of ladders up to
L = 200L=200
rungs (400 spins 1/2) and down to very low temperatures.
Majorana-Time-Reversal Symmetries: A Fundamental Principle for Sign-Problem-Free Quantum Monte Carlo Simulations
