General quantum algorithms for Hamiltonian simulation with applications to a non-Abelian lattice gauge theory

TL;DR

This paper introduces general quantum algorithms for simulating Hamiltonians in lattice gauge theories, focusing on efficiency and gauge invariance, with detailed resource analysis for SU(2) gauge theory and potential extensions.

Contribution

It develops versatile quantum algorithms for Hamiltonian simulation in lattice gauge theories, emphasizing gauge-invariant formulations that reduce computational costs and maintain symmetry.

Findings

Algorithms efficiently simulate non-Abelian gauge interactions.

Gauge-invariant formulations simplify algorithms and lower costs.

Complete resource analysis for SU(2) gauge theory in 1+1 dimensions.

Abstract

With a focus on universal quantum computing for quantum simulation, and through the example of lattice gauge theories, we introduce rather general quantum algorithms that can efficiently simulate certain classes of interactions consisting of correlated changes in multiple (bosonic and fermionic) quantum numbers with non-trivial functional coefficients. In particular, we analyze diagonalization of Hamiltonian terms using a singular-value decomposition technique, and discuss how the achieved diagonal unitaries in the digitized time-evolution operator can be implemented. The lattice gauge theory studied is the SU(2) gauge theory in 1+1 dimensions coupled to one flavor of staggered fermions, for which a complete quantum-resource analysis within different computational models is presented. The algorithms are shown to be applicable to higher-dimensional theories as well as to other Abelian and non-Abelian gauge theories. The example chosen further demonstrates the importance of adopting efficient theoretical formulations: it is shown that an explicitly gauge-invariant formulation using loop, string, and hadron degrees of freedom simplifies the algorithms and lowers the cost compared with the standard formulations based on angular-momentum as well as the Schwinger-boson degrees of freedom. The loop-string-hadron formulation further retains the non-Abelian gauge symmetry despite the inexactness of the digitized simulation, without the need for costly controlled operations. Such theoretical and algorithmic considerations are likely to be essential in quantumly simulating other complex theories of relevance to nature.