Gauge Symmetry in Quantum Simulation

TL;DR

This paper develops a comprehensive framework for quantum simulation of non-Abelian gauge theories, clarifying gauge symmetry handling, introducing efficient protocols, and demonstrating practical implementations relevant to real-world QCD.

Contribution

It presents universal principles for gauge symmetry treatment in quantum simulation, including both singlet and non-singlet approaches, with explicit circuit constructions and error analysis.

Findings

Validated convergence and error bounds through classical simulations.

Introduced efficient Hamiltonian simulation protocols for SU(N) gauge theories.

Provided scalable circuit recipes for practical quantum simulations.

Abstract

Quantum simulation of non-Abelian gauge theories requires careful handling of gauge redundancy. We address this challenge by presenting universal principles for treating gauge symmetry that apply to any quantum simulation approach, clarifying that physical states need not be represented solely by gauge singlets. Both singlet and non-singlet representations are valid, with distinct practical trade-offs, which we elucidate using analogies to BRST quantization. We demonstrate these principles within a complete quantum simulation framework based on the orbifold lattice, which enables explicit and efficient circuit constructions relevant to real-world QCD. For singlet-based approaches, we introduce a Haar-averaging projection implemented via linear combinations of unitaries, and analyze its cost and truncation errors. We also introduce an efficient simulation protocol with an additional term to the Hamiltonian that eliminates non-singlet states from the low-energy spectrum. Beyond the singlet-approach, we show how non-singlet approaches can yield gauge-invariant observables through wave packets and string excitations. This non-singlet approach is proven to be both universal and efficient. Working in temporal gauge, we provide explicit mappings of lattice Yang-Mills dynamics to Pauli-string Hamiltonians suitable for Trotterization. Classical simulations of small systems validate convergence criteria and quantify truncation and Trotter errors, showing concrete resource estimates and scalable circuit recipes for SU$(N)$ gauge theories. Our framework provides both conceptual clarity and practical tools toward quantum advantage in simulating non-Abelian gauge theories.