Quantum transport on networks for supervised classification

Abstract

Classification, the computational process of categorizing an input into pre-existing classes, is now a cornerstone in modern computation in the era of machine learning. Here we propose a new type of quantum classifier, based on quantum transport of particles in a trained quantum network. The classifier is based on sending a quantum particle into a network and measuring the particle's exit point, which serves as a "class" and can be determined by changing the network parameters. Using this scheme, we demonstrate three examples of classification; in the first, wave functions are classified according to their overlap with predetermined (random) groups. In the second, we classify wave-functions according to their level of localization. Both examples use small training sets and achieve over 90\% precision and recall. The third classification scheme is a "real-world problem", concerning classification of catalytic aromatic-aldehyde substrates according to their reactivity. Using experimental data, the quantum classifier reaches an average 86\% classification accuracy. We show that the quantum classifier outperforms its classical counterpart for these examples, thus demonstrating quantum advantage, especially in the regime of "small data". These results pave the way for a novel classification scheme, which can be implemented as an algorithm, and potentially realized experimentally on quantum hardware such as photonic networks.