HamQASBench: A Hamiltonian-Informed Diagnostic Benchmark for Evaluating Quantum Architecture Search

2026-07-06

AI Summary

This work addresses critical limitations in existing quantum architecture search (QAS) benchmarks, which categorize problems solely by molecular species or qubit count while ignoring Hamiltonian structure and relying exclusively on energy accuracy—obscuring structural failure modes. To overcome this, we introduce HamQASBench, the first Hamiltonian structure-aware benchmarking framework. It classifies 11 molecules into five categories based on Pauli operator basis, computational basis representation, and ground-state entanglement. Leveraging per-qubit entanglement analysis and pairwise state fidelity, our framework diagnoses structural performance of QAS methods. Through Hamiltonian fingerprinting, critical circuit extraction, and multi-paradigm comparisons, we uncover five hidden failure modes: over-parameterization in minimal-entanglement regimes, degenerate eigenstate locking, strong-correlation representation bottlenecks, topology-induced routing failures, and scalability limits induced by search space expansion.

Abstract

Quantum Architecture Search (QAS) automates the design of parameterized quantum circuits for variational quantum algorithms, yet existing benchmarks organize instances by molecular identity or qubit count -- criteria agnostic to Hamiltonian structure -- and rely solely on energy accuracy, which cannot detect structural failures such as over-parameterization on near-product ground states. We introduce HamQASBench, a Hamiltonian-informed diagnostic benchmark organizing 11 molecules into five structural tiers via fingerprints derived from the Pauli operator basis, computational basis representation, and ground-state entanglement. A post-hoc critical-structure extraction procedure identifies minimal circuits consistent with each tier's requirements, complementing energy-based evaluation with per-qubit entanglement analysis and pairwise state fidelity. Benchmarking five QAS methods across four paradigms reveals failure modes invisible to conventional metrics: over-parameterization in the minimalism regime, eigenstate commitment under degeneracy, a representation bottleneck in strongly correlated systems, topology-induced routing failure, and circuit search space growth as a scalability bottleneck.

Problem

• Quantum Architecture Search
• Hamiltonian structure
• benchmarking
• structural failure
• entanglement

Innovation

• Hamiltonian-informed benchmark
• Quantum Architecture Search
• structural tiers
• entanglement analysis
• critical-structure extraction