Efficient Discrete Feature Encoding for Variational Quantum Classifier

TL;DR

This paper introduces an efficient quantum encoding method using QRAC for discrete features in variational quantum classifiers, demonstrating improved training speed and effectiveness on real-world datasets.

Contribution

It proposes the use of quantum random-access coding (QRAC) for efficient discrete feature encoding in VQC, addressing a gap in existing quantum mapping strategies.

Findings

QRAC enables faster VQC training by reducing qubit requirements.

Encoding strategies have specific limitations and capabilities.

QRAC improves classification performance on real-world datasets.

Abstract

Recent days have witnessed significant interests in applying quantum-enhanced techniques for solving a variety of machine learning tasks. Variational methods that use quantum resources of imperfect quantum devices with the help of classical computing techniques are popular for supervised learning. Variational quantum classification (VQC) is one of such methods with possible quantum advantage in using quantum-enhanced features that are hard to compute by classical methods. Its performance depends on the mapping of classical features into a quantum-enhanced feature space. Although there have been many quantum-mapping functions proposed so far, there is little discussion on efficient mapping of discrete features, such as age group, zip code, and others, which are often significant for classifying datasets of interest. We first introduce the use of quantum random-access coding (QRAC) to map such discrete features efficiently into limited number of qubits for VQC. In numerical simulations, we present a range of encoding strategies and demonstrate their limitations and capabilities. We experimentally show that QRAC can help speeding up the training of VQC by reducing its parameters via saving on the number of qubits for the mapping. We confirm the effectiveness of the QRAC in VQC by experimenting on classification of real-world datasets with both simulators and real quantum devices.