Encoding Matters: Benchmarking Binary and D-ary Representations for Quantum Combinatorial Optimization

Fuente: arXiv
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Autores principales: Bhat, Shashank Sanjay, Wang, Peiyong, West, Joseph, Parampalli, Udaya
Formato: Preprint
Publicado: 2026
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author Bhat, Shashank Sanjay
Wang, Peiyong
West, Joseph
Parampalli, Udaya
author_facet Bhat, Shashank Sanjay
Wang, Peiyong
West, Joseph
Parampalli, Udaya
contents Combinatorial optimization problems are typically formulated using Quadratic Unconstrained Binary Optimization (QUBO), where constraints are enforced through penalty terms that introduce auxiliary variables and rapidly increase Hamiltonian complexity, limiting scalability on near term quantum devices. In this work, we systematically study Quadratic Unconstrained D-ary Optimization (QUDO) as an alternative formulation in which decision variables are encoded directly in higher dimensional Hilbert spaces. We demonstrate that QUDO naturally captures structural constraints across a range of problem classes, including the Traveling Salesman Problem, two variants of the Vehicle Routing Problem, graph coloring, job scheduling, and Max-K-Cut, without the need for extensive penalty constructions. Using a qudit-level implementation of the Quantum Approximate Optimization Algorithm (qudit QAOA), we benchmark these formulations against their binary QUBO counterparts and exact classical solutions. Our study show consistently improved approximation ratios and substantially reduced computational overhead at comparable circuit depths, highlighting QUDO as a scalable and expressive representation for quantum combinatorial optimization.
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spellingShingle Encoding Matters: Benchmarking Binary and D-ary Representations for Quantum Combinatorial Optimization
Bhat, Shashank Sanjay
Wang, Peiyong
West, Joseph
Parampalli, Udaya
Quantum Physics
Combinatorial optimization problems are typically formulated using Quadratic Unconstrained Binary Optimization (QUBO), where constraints are enforced through penalty terms that introduce auxiliary variables and rapidly increase Hamiltonian complexity, limiting scalability on near term quantum devices. In this work, we systematically study Quadratic Unconstrained D-ary Optimization (QUDO) as an alternative formulation in which decision variables are encoded directly in higher dimensional Hilbert spaces. We demonstrate that QUDO naturally captures structural constraints across a range of problem classes, including the Traveling Salesman Problem, two variants of the Vehicle Routing Problem, graph coloring, job scheduling, and Max-K-Cut, without the need for extensive penalty constructions. Using a qudit-level implementation of the Quantum Approximate Optimization Algorithm (qudit QAOA), we benchmark these formulations against their binary QUBO counterparts and exact classical solutions. Our study show consistently improved approximation ratios and substantially reduced computational overhead at comparable circuit depths, highlighting QUDO as a scalable and expressive representation for quantum combinatorial optimization.
title Encoding Matters: Benchmarking Binary and D-ary Representations for Quantum Combinatorial Optimization
topic Quantum Physics
url https://arxiv.org/abs/2602.07357