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Wiese, Computational Complexity and Fundamental Limitations to Fermionic Quantum Monte Carlo Simulations, Physical Review Letters, 2005","review_link":"https://doi.org/10.1103/PhysRevLett.94.170201","review_verified":"true","summary":"Computer simulations of many interacting electrons often require adding huge numbers of positive and negative terms that nearly cancel, so errors grow exponentially with system size; this is the sign problem. 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