PT  - JOURNAL ARTICLE
AU  - Hangleiter, Dominik
AU  - Roth, Ingo
AU  - Nagaj, Daniel
AU  - Eisert, Jens
TI  - Easing the Monte Carlo sign problem
AID  - 10.1126/sciadv.abb8341
DP  - 2020 Aug 01
TA  - Science Advances
PG  - eabb8341
VI  - 6
IP  - 33
4099  - http://advances.sciencemag.org/content/6/33/eabb8341.short
4100  - http://advances.sciencemag.org/content/6/33/eabb8341.full
SO  - Sci Adv2020 Aug 01; 6
AB  - Quantum Monte Carlo (QMC) methods are the gold standard for studying equilibrium properties of quantum many-body systems. However, in many interesting situations, QMC methods are faced with a sign problem, causing the severe limitation of an exponential increase in the runtime of the QMC algorithm. In this work, we develop a systematic, generally applicable, and practically feasible methodology for easing the sign problem by efficiently computable basis changes and use it to rigorously assess the sign problem. Our framework introduces measures of non-stoquasticity that—as we demonstrate analytically and numerically—at the same time provide a practically relevant and efficiently computable figure of merit for the severity of the sign problem. Complementing this pragmatic mindset, we prove that easing the sign problem in terms of those measures is generally an NP-complete task for nearest-neighbor Hamiltonians and simple basis choices by a reduction to the MAXCUT-problem.