Quantum Circuit Learning Using Non-Integrable System Dynamics

Quantum machine learning is an approach that aims to improve the performance of machine learning methods by leveraging the properties of quantum computers. In quantum circuit learning (QCL), a supervised learning method that can be implemented using variational quantum algorithms (VQAs), the process of encoding input data into quantum states has been widely discussed for its important role on the expressive power of learning models. In particular, the properties of the eigenvalues of the Hamiltonian used for encoding significantly influence model performance. Recent encoding methods have demonstrated that the expressive power of learning models can be enhanced by applying exponentially large magnetic fields proportional to the number of qubits. However, this approach poses a challenge as it requires exponentially increasing magnetic fields, which are impractical for implementation in large-scale systems. Here, we propose a QCL method that leverages a non-integrable Hamiltonian for encoding, aiming to achieve both enhanced expressive power and practical feasibility. We find that the thermalization properties of non-integrable systems over long timescales, implying that the energy difference has a low probability to be degenerate, lead to an enhanced expressive power for QCL. Since the required magnetic field strength remains within a practical range, our approach to using the non-integrable system is suitable for large-scale quantum computers. Our results bridge the dynamics of non-integrable systems and the field of quantum machine learning, suggesting the potential for significant interdisciplinary contributions.