用格罗弗算法加速神经网络权重优化,提升精度并减少对量子比特的需求。
Quantum-Enhanced Weight Optimization for Neural Networks Using Grover's Algorithm
- 用格罗弗搜索算法直接搜寻最优权重,无需计算梯度。
- 在小数据集上测试损失降低58.75%,准确率提升35.25%。
- 适用于深度网络,仅需少量量子比特,适合近期量子硬件。
传统混合量子-经典神经网络将量子计算用于构建具有量子特性的网络,再通过经典方法优化。本文提出新策略:利用量子计算优化经典神经网络的权重。设计一种格罗弗量子搜索算法实例,在训练过程中加速寻找最优参数,替代传统的基于梯度下降的反向传播方法。该方法避免了梯度爆炸、消失及凸性问题,且不依赖梯度计算,结合经典架构的稳定性与格罗弗算法在高维空间中的二次加速优势,使测试损失降低58.75%,测试准确率提升35.25%,优于经典优化方法。实验基于scikit-learn的Digits数据集,对含3个隐藏层的神经网络实现平均准确率97.7%。本方法具备可扩展性,且所需量子比特数量远低于其他量子神经网络方案,适配未来短期内逻辑量子比特有限的硬件环境。
原文摘要 · Abstract (English)
The main approach to hybrid quantum-classical neural networks (QNN) is employing quantum computing to build a neural network (NN) that has quantum features, which is then optimized classically. Here, we propose a different strategy: to use quantum computing in order to optimize the weights of a classical NN. As such, we design an instance of Grover's quantum search algorithm to accelerate the search for the optimal parameters of an NN during the training process, a task traditionally performed using the backpropagation algorithm with the gradient descent method. Indeed, gradient descent has issues such as exploding gradient, vanishing gradient, or convexity problem. Other methods tried to address such issues with strategies like genetic searches, but they carry additional problems like convergence consistency. Our original method avoids these issues -- because it does not calculate gradients -- and capitalizes on classical architectures' robustness and Grover's quadratic speedup in high-dimensional search spaces to significantly reduce test loss (58.75%) and improve test accuracy (35.25%), compared to classical NN weight optimization, on small datasets. Unlike most QNNs that are trained on small datasets only, our method is also scalable, as it allows the optimization of deep networks; for an NN with 3 hidden layers, trained on the Digits dataset from scikit-learn, we obtained a mean accuracy of 97.7%. Moreover, our method requires a much smaller number of qubits compared to other QNN approaches, making it very practical for near-future quantum computers that will still deliver a limited number of logical qubits.
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