Scientists have developed a quantum-classical computational framework to study many-fermion response and structure. The new approach, published in Physics Letters B, integrates quantum computing with classical computing techniques to resolve the long-standing bottleneck that has limited ab initio calculations of strongly interacting systems.

Response functions are fundamental physical observables for probing the structural and dynamical properties of strongly correlated quantum many-body systems, with extensive applications in nuclear physics, quantum chemistry and other fields.

But there is a major challenge: the Hilbert space for such strongly correlated quantum many-body problems grows exponentially with the number of particles. This makes ab initio calculations for systems larger than a moderate size impossible even for the most powerful classical computers.

Quantum computing, which is well-suited for large-scale computations in quantum many-body physics, offers a promising avenue to overcome this bottleneck. The development of quantum computing technologies, as well as theories and algorithms tailored for quantum many-body problems, is currently one of the leading research focuses in the interdisciplinary field of nuclear physics and quantum computing worldwide.

Researchers from the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS) and their collaborators have built an efficient and scalable quantum-classical hybrid framework to solve large-scale many-fermion problems.

The framework includes a low-overhead quantum encoding scheme independently developed by the team. As a result, it significantly reduces the cost of circuit compilation. It also performs a unified self-consistent calculation of the full bound-state spectra and response functions of many-fermion systems under realistic nuclear interactions.

To check whether the new framework works, the researchers performed precise calculations of the excitation energy spectra of oxygen-19. The results showed that the calculations from this framework matched those obtained from classical computations.

The researchers said this adaptable framework opens a new path for ab initio studies of nuclear structure and nuclear reactions, while also provides support for the application of quantum computing in the field of strongly correlated many-body systems.

This work was carried out jointly by IMP, the Guangdong Laboratory of Advanced Energy Science and Technology, Iowa State University, and the Lawrence Berkeley National Laboratory.