Shell-model study of 58Ni using quantum computing algorithm

This study presents a simulated quantum computing approach for the investigation into the shell-model energy levels of ⁵⁸Ni through the application of the variational quantum eigensolver (VQE) method in combination with a problem-specific ansatz. The primary objective is to achieve a fully accurate low-lying energy spectrum of ⁵⁸Ni. The chosen isotope, ⁵⁸Ni is particularly interesting in nuclear physics through its role in astrophysical reactions while also being a simple but non-trivial nucleus for shell-model study, it being two particles outside a closed shell. Our ansatz, along with the VQE method are shown to be able to reproduce exact energy values for the ground state and first and second excited states. We compare a classical shell model code, the values obtained by diagonalization of the Hamiltonian after qubit mapping, and a noiseless simulated ansatz+VQE simulation. The exact agreement between classical and qubit-mapped diagonalization shows the correctness of our method, and the high accuracy of the simulation means that the ansatz is suitable to allow a full reconstruction of the full nuclear wave function.