Density of states approach to dense quantum systems

We develop a first-principle generalized density-of-states method for numerically studying quantum field theories with a complex action. As a proof of concept, we show that with our approach we can numerically solve the strong sign problem of the Z₃ spin model at finite density. Our results are confirmed by standard simulations of the theory dual to the considered model, which is free from a sign problem. Our method opens new perspectives on ab initio simulations of cold dense quantum systems, and in particular of Yang-Mills theories with matter at finite densities, for which Monte Carlo-based importance sampling is unable to produce sufficiently accurate results.