Supervised learning with quantum-enhanced feature spaces, Vojtech Havlíček, Antonio D. Córcoles, Kristan Temme, Aram W. Harrow, Abhinav Kandala, Jerry M. Chow, Jay M. Gambetta, 2019Nature, Vol. 567DOI: 10.1038/s41586-019-0980-2 - This foundational paper introduces the concept of quantum-enhanced feature spaces, showing how quantum circuits can embed classical data into high-dimensional Hilbert spaces for machine learning, including a specific example of a quantum feature map.
Supervised Learning with Quantum Computers, Maria Schuld, Francesco Petruccione, 2018 (Springer)DOI: 10.1007/978-3-319-96424-9 - A comprehensive academic textbook that provides mathematical foundations for quantum machine learning, including explanations of quantum feature maps, their construction, and their application in quantum kernel methods.
ZZFeatureMap, Qiskit contributors, 2024 (IBM) - Official documentation for the ZZFeatureMap in Qiskit, offering specific information on its implementation, parameters, and use in building quantum circuits for data encoding, which is relevant to the example in the text.