Accurate Gauge-Invariant Tensor-Network Simulations for Abelian Lattice Gauge Theory in (2+1)D: Ground-State and...

We propose a novel tensor-network method to achieve accurate and efficient simulations of Abelian lattice gauge theories (LGTs) in (2+1)D for both ground-state and real-time dynamics. The first key is to identify a gauge canonical form of gauge-invariant tensor-network states, which already simplifies existing algorithms for (1+1)D LGTs. The second key is to employ the gauge canonical form of a projected entangled-pair state (PEPS) combining with variational Monte Carlo, enabling efficient computations for (2+1)D LGTs. We demonstrate the versatile capability of this approach for accurate ground-state simulation of pure Z_{2}, Z_{3}, and Z_{4} gauge theory, odd-Z_{2} gauge theories, and Z_{2} gauge theory coupled to hard-core bosons, on square lattices up to 32×32. Furthermore, we demonstrate that it allows for accurate simulations of real-time dynamics up to long time, exemplified by the dynamics of elementary excitations of the deconfined Z_{2} gauge field at 10×10. This is also the first example of simulating the real-time dynamics of PEPS with variational Monte Carlo, whose impact may extend beyond gauge theory. Our Letter establishes gauge-invariant PEPS as a powerful approach for both ground-state and dynamical simulations, opening up a new avenue for nonperturbatively studying (2+1)D LGTs.