arXiv:2608.05595quant-phcs.DC2026-08

量子机器学习中,用后期融合替代重建,大幅降低计算成本且更抗噪声。

How Much Reconstruction Does Quantum Machine Learning Need? Late Fusion of Independently Trained Quantum Subcircuits

  • 各子电路独立训练测量,由小型经典模型在决策层融合输出。
  • 准确率与完整重建几乎无差(误差≤0.04),但耗时呈指数级下降。
  • 可自诊断任务对重建的需求,适合资源受限的量子设备部署。

电路切割使大型量子神经网络可在小设备上以独立子电路运行,但通过重建恢复输出会带来随切割数指数增长的经典采样开销——这是以往工作的主要运行时瓶颈。本文探讨:在机器学习任务中,这一步是否必要?提出用后期融合替代重建:各子电路独立训练并测量,再由小型经典头部组合输出,实现线性开销的决策层融合,借鉴自多模态学习。为量化权衡,引入可调的量子性旋钮 $Q$,以及切割纠缠诊断指标(104次实验中斯皮尔曼相关系数 $ρ=0.59$)。在合成数据与标准数据集上,独立训练的后期融合在所有控制扫描点及经典基准测试中,准确率与全重建相差不超过0.04,且代价呈指数级降低;同时显著更鲁棒于采样噪声和设备噪声。受控纠缠数据实验定位了融合失效的边界。本文不宣称超越经典机器学习——与近期基准一致,当前数据集下量子未提供准确率优势。因此,后期融合是电路切割量子机器学习中高效、抗噪、自诊断的重建替代方案。

原文摘要 · Abstract (English)

Circuit cutting lets a large quantum neural network (QNN) run as independent subcircuits on small devices, but rebuilding its outputs by reconstruction carries a classical sampling overhead exponential in the number of cuts - the dominant runtime cost in prior work. We ask whether, for machine-learning tasks, this step is necessary, and replace it with late fusion: each subcircuit is trained and measured independently, and a small classical head combines their outputs - a linear-cost, decision-level combination borrowed from multimodal learning. To characterize the trade-off we introduce a quantumness dial $Q$, a tunable reconstruction budget interpolating from pure fusion to full reconstruction, and a cut-entanglement diagnostic that indicates how much reconstruction a task needs (Spearman $ρ=0.59$ over $104$ runs). Across synthetic and standard datasets, independently trained late fusion matches full reconstruction accuracy within $0.04$ at every point of the controlled sweep and on every classical benchmark, at exponentially lower cost; it is also markedly more robust to shot and device noise. Controlled entangled-data experiments locate the boundary where fusion must fail. We do not claim advantage over classical machine learning - consistent with recent benchmarking, quantum offers no accuracy edge on these datasets. Late fusion is thus an efficient, noise-robust, self-characterizing alternative to reconstruction for circuit-cutting QML.

量子机器学习电路切割后期融合噪声鲁棒

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