论文标题

带宽可以在量子内核模型中概括

Bandwidth Enables Generalization in Quantum Kernel Models

论文作者

Canatar, Abdulkadir, Peters, Evan, Pehlevan, Cengiz, Wild, Stefan M., Shaydulin, Ruslan

论文摘要

已知量子计算机可以在某些专业设置中对经典的最先进的机器学习方法提供加速。例如,已证明量子内核方法可以在离散对数问题的学习版本上提供指数加速。了解量子模型的概括对于实现实际利益问题的类似加速至关重要。最近的结果表明,量子特征空间的指数大小阻碍了概括。尽管这些结果表明量子模型在量子数数量较大时无法概括,但在本文中,我们表明这些结果取决于过度限制性的假设。我们通过改变称为量子内核带宽的超参数来考虑更广泛的模型。我们分析了大量限制,并为可以以封闭形式求解的量子模型的概括提供了明确的公式。具体而言,我们表明,更改带宽的值可以使模型从不能概括到任何目标函数到良好的概括目标的概括。我们的分析表明,带宽如何控制内核积分操作员的光谱,从而如何控制模型的电感偏置。我们从经验上证明,我们的理论正确预测带宽如何影响质量模型在具有挑战性的数据集上的概括,包括远远超出我们理论假设的数据集。我们讨论了结果对机器学习中量子优势的含义。

Quantum computers are known to provide speedups over classical state-of-the-art machine learning methods in some specialized settings. For example, quantum kernel methods have been shown to provide an exponential speedup on a learning version of the discrete logarithm problem. Understanding the generalization of quantum models is essential to realizing similar speedups on problems of practical interest. Recent results demonstrate that generalization is hindered by the exponential size of the quantum feature space. Although these results suggest that quantum models cannot generalize when the number of qubits is large, in this paper we show that these results rely on overly restrictive assumptions. We consider a wider class of models by varying a hyperparameter that we call quantum kernel bandwidth. We analyze the large-qubit limit and provide explicit formulas for the generalization of a quantum model that can be solved in closed form. Specifically, we show that changing the value of the bandwidth can take a model from provably not being able to generalize to any target function to good generalization for well-aligned targets. Our analysis shows how the bandwidth controls the spectrum of the kernel integral operator and thereby the inductive bias of the model. We demonstrate empirically that our theory correctly predicts how varying the bandwidth affects generalization of quantum models on challenging datasets, including those far outside our theoretical assumptions. We discuss the implications of our results for quantum advantage in machine learning.

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