Many-body quantum states with exact conservation of non-Abelian and lattice symmetries through variational Monte Carlo
Tom Vieijra, Jannes Nys
Abstract
Optimization of quantum states using the variational principle has recently seen an upsurge due to developments of increasingly expressive wave functions. In order to improve on the accuracy of the Ans\"atze, it is a time-honored strategy to impose the systems' symmetries. We present an Ansatz where global non-Abelian symmetries are inherently embedded in its structure. We extend the model to incorporate lattice symmetries as well. We consider the prototypical example of the frustrated two-dimensional ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ model on a square lattice, for which eigenstates have been hard to model variationally. Our novel approach guarantees that the obtained ground state will have total spin zero. Benchmarks on the 2D ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ model demonstrate its state-of-the-art performance in representing the ground state. Furthermore, our methodology permits to find the wave functions of excited states with definite quantum numbers associated to the considered symmetries (including the non-Abelian ones), without modifying the architecture of the network.