用复数酉变换提升神经网络置信度校准,显著降低错误率。
Complex-Valued Unitary Representations as Classification Heads for Improved Uncertainty Quantification in Deep Neural Networks
- 将特征投影到复数希尔伯特空间,通过可学习酉变换演化
- 在CIFAR-10上校准误差降至0.0146,优于标准softmax头2.4倍
- 适合需要高置信度可靠性的安全关键场景
现代深度神经网络虽预测准确,但置信度常不反映真实正确概率。本文提出一种受量子启发的分类头架构:将主干特征投影至复数希尔伯特空间,并通过参数化于凯利映射的可学习酉变换演化。通过控制性实验(共享单个主干,对比轻量可替换头),我们隔离了复数酉表示对校准的影响。CIFAR-10上的消融研究显示,酉幅值头(复数特征经凯利酉变换演化,以模长和softmax读出)的期望校准误差(ECE)为0.0146,相比标准softmax头(0.0355)提升2.4倍,相比温度缩放(0.0510)提升3.5倍。令人意外的是,改用基于玻恩规则的测量层(量子力学启发)反而使校准恶化至ECE=0.0819。在CIFAR-10H人类不确定性基准上,波函数头在与人类软标签的KL散度上达到最低(0.336),表明复数表示更贴合人类感知模糊性结构。我们从特征空间几何角度理论分析了保范酉动力学与校准的关系,报告了其在分布外检测和情感分析中的负结果以界定方法边界,并讨论了其在安全关键应用中的实际意义。代码已公开。
原文摘要 · Abstract (English)
Modern deep neural networks achieve high predictive accuracy but remain poorly calibrated: their confidence scores do not reliably reflect the true probability of correctness. We propose a quantum-inspired classification head architecture that projects backbone features into a complex-valued Hilbert space and evolves them under a learned unitary transformation parameterised via the Cayley map. Through a controlled hybrid experimental design - training a single shared backbone and comparing lightweight interchangeable heads - we isolate the effect of complex-valued unitary representations on calibration. Our ablation study on CIFAR-10 reveals that the unitary magnitude head (complex features evolved under a Cayley unitary, read out via magnitude and softmax) achieves an Expected Calibration Error (ECE) of 0.0146, representing a 2.4x improvement over a standard softmax head (0.0355) and a 3.5x improvement over temperature scaling (0.0510). Surprisingly, replacing the softmax readout with a Born rule measurement layer - the quantum-mechanically motivated approach - degrades calibration to an ECE of 0.0819. On the CIFAR-10H human-uncertainty benchmark, the wave function head achieves the lowest KL-divergence (0.336) to human soft labels among all compared methods, indicating that complex-valued representations better capture the structure of human perceptual ambiguity. We provide theoretical analysis connecting norm-preserving unitary dynamics to calibration through feature-space geometry, report negative results on out-of-distribution detection and sentiment analysis to delineate the method's scope, and discuss practical implications for safety-critical applications. Code is publicly available.
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