AB INITIO AND QUANTUM COMPUTATION APPROACHES TO STUDY NUCLEAR STRUCTURE

Abstract

The development of ab initio methods in nuclear physics has been driven by ad vancements in computational power and long-term efforts to explore nuclear prop erties from first principles. Among these methods, the no-core shell model (NCSM) stands out as particularly successful in studying low-mass nuclei on the nuclear chart. This approach leverages realistic nucleon-nucleon interactions derived from meson-exchange theory or chiral effective field theory, providing a robust framework for understanding nuclear structure. At the same time, recent progress in quantum science and technology offers fresh opportunities to investigate quantum many-body systems like atomic nuclei. Integrating ab initio methods with quantum computa tion and quantum information techniques holds the potential to revolutionize our understanding of atomic nuclei.The aim of the present thesis is to study the nuclear structural properties of lower sd-shell nuclei, specifically neon and sodium nuclei, which pose challenges to the ab initio methods because of exotic features across the isotopic chains. Since the exact form of the nuclear potential is still unknown, the main goal is to examine which interaction is the most suitable for a chosen set of nuclei or an isotopic chain. We have applied different realistic nucleon-nucleon (NN) interactions i.e. the in side non–local outside Yukawa (INOY), the charge–dependent Bonn 2000 (CDB2K) potential, and the next-to-next-to-next-to-leading order (N3LO) potential in the NCSM method to address this issue. We have reached basis sizes up to Nmax = 6 for 18Ne and, Nmax = 4 for 19−24Ne and 20−23Na, with M-scheme dimensions up to 1.1 billion. We have determined the low-lying energy spectra of natural parity for 18−24Ne and both positive and negative parity states for the 20−23Na isotopes and investigated the level structures. Overall, our NCSM results are consistent with the available experimental data. The INOY interaction without the inclusion of the three-body force correctly reproduces the g.s. binding energies for nuclei around N =Z, which indicates that the INOY force produces effects similar to those pro duced by including three-nucleon forces. This is an encouraging result for the goal of finding a way of calculating the structure of atomic nuclei microscopically using only the NN interaction as input. We have also calculated electromagnetic observ ables such as quadrupole moment, reduced electric quadrupole transition strength, magnetic moment, and reduced dipole magnetic transition strength. We found that the INOY interaction gives the best description of the ground state energies, while the N3LO interaction best reproduces the point-proton radii. We have extended the application of the ab initio NCSM approach, which gives the reliable description of nuclei up to A = 16, to study lower sd-shell nuclei of Ne and Na-chain. With increasing mass number, the dimension of the Hamiltonian matrix increases in the NCSM method, which becomes computationally challenging. To get around this problem, a new technique is proposed in which effective valence shell interac tions are built using the NCSM wave functions and the Okubo-Lee-Suzuki trans formation method. Newly developed microscopic effective sd-shell interactions are chiral N3LO, J-matrix inverse scattering potential (JISP16), Daejeon16 (DJ16), and monopole-modified DJ16 (DJ16A). These interactions are usually given in isospin symmetric form, and spectra obtained for mirror pairs of nuclei using such interac tions would be degenerate. We aim to develop and test new sets of isospin symmetry breaking (ISB) interactions based on microscopic DJ16A interaction that can explain the mirror energy difference (MED) among mirror pairs within sd-shell. We con sider two different types of Coulomb two-body matrix elements, Coulomb-CD and Coulomb-w/SRC, along with the charge symmetry breaking (CSB) and charge in dependence breaking (CIB) interactions to construct them.