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Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D. Particles and fields

Exact ground-state properties of the SU(2) Hamiltonian lattice gauge theory

Siu A. Chin, O.S. van Roosmalen, E. A. Umland, S. E. Koonin

Published Jun 15, 1985• 41 citations
Publisher

Abstract

The SU(2) Hamiltonian lattice gauge theory is shown explicitly to be equivalent to a nonrelativistic quantum many-body problem in ${S}^{3}$. By exploiting this equivalence, a many-body Monte Carlo algorithm is devised to solve for its ground-state properties. To the extent that a trial wave function consisting of a product of single-plaquette functions is a good approximation to the exact ground state, the present Monte Carlo method is shown to be an efficient means of calculating the ground-state energy with high precision.

DOI
10.1103/physrevd.31.3201

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The SU(2) Hamiltonian lattice gauge theory is shown explicitly to be equivalent to a nonrelativistic quantum many-body problem in S3{S}^{3}S3. By exploiting this equivalence, a many-body Monte Carlo algorithm is devised to solve for its ground-state properties. To the extent that a trial wave function consisting of a product of single-plaquette functions is a good approximation to the exact ground state, the present Monte Carlo method is shown to be an efficient means of calculating the ground-state energy with high precision.
We propose a new Monte Carlo algorithm for the numerical study of general lattice models in Hamiltonian form. The algorithm is based on an initial ansatz for the ground state wave function depending on a set of free parameters which are dynamically optimized. The method is discussed in detail and the results are reported from explicit simulations of a U(1) N chain, a degenerate limit of U(1) lattice gauge theory in 2+12+12+1 dimensions.
Gauge theories describe fundamental interactions in the standard model of particle physics and build effective theories in condensed matter physics. Being notoriously hard to simulate, these theories are commonly regularized as lattice gauge theories which can be evaluated with high precision through Monte Carlo algorithms or variational methods. However, Monte Carlo algorithms are not applicable in all regimes due to the sign problem; while variational methods, quantum and classical alike, only give upper-bounds on the ground-state energy. Their precision crucially depends on the chosen ansatz. Here, we present a framework based on a hierarchy of semidefinite programs to yield increasingly good lower-bounds on the ground-state energy and propagate these bounds to extended observables like Wilson loops and mesonic strings. We demonstrate the numerical capabilities by applying the algorithm to a (1+1)-dimensional Z2\mathbb{Z}_2Z2​ theory with dynamic fermionic matter and its pure-gauge version in (2+1)-dimensions. In both cases, we obtain certified intervals for the ground-state energy. For a one-dimensional system with 129 sites, the certified interval has a relative spread of 0.04%0.04\%0.04%. For a two-dimensional system with 97 sites (corresponding to a 7×87 \times 87×8 lattice), the relative spread is 2.08%2.08\%2.08%. Beyond energy estimates, the proposed method provides rigorous bounds on both short- and long-range observables such as Wilson loops over multiple plaquettes and the magnitude of the mesonic string. The method can be both used as a computational microscope into many-body physics and a way to certify results of quantum simulators.
We present a neural network wave function framework for solving non-Abelian lattice gauge theories in a continuous group representation. Using a combination of SU(2) equivariant neural networks alongside an SU(2) invariant, physics-inspired ansatz, we learn a parametrization of the ground state wave function of SU(2) lattice gauge theory in 2+1 and 3+1 dimensions. Our method, performed in the Hamiltonian formulation, has a straightforward generalization to SU(N). We benchmark our approach against a solely invariant ansatz by computing the ground state energy, demonstrating the need for bespoke gauge equivariant transformations. We evaluate the Creutz ratio and average Wilson loop, and obtain results in strong agreement with perturbative expansions. Our method opens up an avenue for studying lattice gauge theories beyond one dimension, with efficient scaling to larger systems, and in a way that avoids both the sign problem and any discretization of the gauge group.
We propose a new ansatz for the ground-state wave function of quantum many-body systems on a lattice. The key idea is to cover the lattice with plaquettes and obtain a state whose configurational weights can be optimized by means of a variational Monte Carlo algorithm. Such a scheme applies to any dimension, without any 'sign' instability. We show results for various two-dimensional spin models (including frustrated ones). A detailed comparison with available exact results, as well as with variational methods based on different ansatze, is offered. In particular, our numerical estimates are in quite good agreement with exact ones for unfrustrated systems, and compare favorably to other methods for frustrated ones.
We propose a new ansatz for the ground-state wave function of quantum many-body systems on a lattice. The key idea is to cover the lattice with plaquettes and obtain a state whose configurational weights can be optimized by means of a variational Monte Carlo algorithm. Such a scheme applies to any dimension, without any 'sign' instability. We show results for various two-dimensional spin models (including frustrated ones). A detailed comparison with available exact results, as well as with variational methods based on different ansatze, is offered. In particular, our numerical estimates are in quite good agreement with exact ones for unfrustrated systems, and compare favorably to other methods for frustrated ones.
Monte Carlo techniques with importance sampling have been extensively applied to lattice gauge theory in the Lagrangian formulation. Unfortunately, it is extremely difficult to compute the excited states using the conventional Monte Carlo algorithm. Our recently developed approach: the Monte Carlo Hamiltonian method, has been designed to overcome the difficulties of the conventional approach. In this paper, we extend the method to many body systems and quantum field theory. The Klein-Gordon field theory is used as a testing ground.