Accurate Gauge-Invariant Tensor Network Simulations for Abelian Lattice Gauge Theory in (2+1)D

Abstract: We propose a novel tensor network method to achieve accurate and efficient simulations of Abelian lattice gauge theories (LGTs) in (2+1)D. The first key is to identify a gauge canonical form (GCF) of gauge-invariant tensor network states, which simplifies existing algorithms already for (1+1)D LGTs. The second key is to employ the GCF of projected entangled-pair state (PEPS) combining variational Monte Carlo, enabling efficient variational optimization for (2+1)D LGT ground states with gauge and matter fields. We demonstrate the versatile capability of this approach for accurate simulation of pure $\mathbb{Z}_2$, $\mathbb{Z}_3$ and $\mathbb{Z}_4$ gauge theory, odd-$\mathbb{Z}_2$ gauge theories, and $\mathbb{Z}_2$ gauge theory coupled to hard-core bosons, on square lattices up to $32\times 32$. Our work establishes gauge-invariant PEPS as a powerful approach to simulate (2+1)D Abelian LGTs.