Efficient Discrete Feature Encoding for Variational Quantum Classifier

Hiroshi Yano, Yudai Suzuki, Kohei M. Itoh, Rudy Raymond, Naoki Yamamoto

Research output: Contribution to journalArticlepeer-review

20 Citations (Scopus)


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.

Original languageEnglish
Article number3103214
JournalIEEE Transactions on Quantum Engineering
Publication statusPublished - 2021


  • Discrete features
  • quantum machine learning
  • quantum random-access coding (QRAC)
  • supervised learning
  • variational quantum algorithms

ASJC Scopus subject areas

  • Software
  • Computer Science (miscellaneous)
  • Condensed Matter Physics
  • Engineering (miscellaneous)
  • Mechanical Engineering
  • Computer Science Applications
  • Electrical and Electronic Engineering


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