Mitigating the Sign Problem Through Basis Rotations

Quantum Monte Carlo simulations of quantum many body systems are plagued by the fermion sign problem. The cost of overcoming the sign problem (and its overall existence) is basis dependent. In this talk, we show how to use sign-free quantum Monte Carlo simulations to minimize the effect of the sign problem by optimizing over the choice of basis on large two-dimensional systems. This can be done despite the fact that the sign problem makes it difficult to even compute the average sign of such a simulation. We numerically illustrate these techniques by decreasing the 'badness' of the sign problem through single-particle basis rotations on one and two dimensional Hubbard systems.