Approximating local properties by tensor network states with constant bond dimension

Abstract

Classical simulation of quantum many-body systems is a fundamental challenge due to their exponentially large Hilbert spaces. Tensor network states are a powerful ansatz to efficiently represent many physically relevant quantum states. A key question is the bond dimension -- which determines the number of parameters in the ansatz -- required to approximate all local properties to accuracy $δ$. In one dimension, we prove that an area law for the Rényi entanglement entropy $R_α$ with index $α<1$ implies a matrix product state representation with bond dimension $\operatorname{poly}(1/δ)$. For (at most constant-fold degenerate) ground states of one-dimensional gapped Hamiltonians, a bond dimension almost linear in $1/δ$ suffices. In two dimensions, an area law for $R_α(α<1)$ implies a projected entangled pair state representation with bond dimension $e^{O(1/δ)}$. In both one and two dimensions, analogous results are obtained for states with logarithmic corrections to the area law. These findings rigorously justify the common practice of using a system-size-independent bond dimension in tensor network simulations.