Weak entanglement approximation for nuclear structure

TL;DR

This paper introduces a weak entanglement approximation for nuclear structure calculations, significantly reducing computational complexity while maintaining key spectral features by leveraging low entanglement between proton and neutron sectors.

Contribution

It presents a novel approximation method that truncates the basis based on weak entanglement, improving efficiency in shell model calculations for nuclei.

Findings

Reduces basis dimension by many orders of magnitude.

Preserves essential features of nuclear spectra.

Effective for heavy, neutron-rich nuclides.

Abstract

The interacting shell model, a configuration-interaction method, is a venerable approach for low-lying nuclear structure calculations; but it is hampered by the exponential growth of its basis dimension as one increases the single-particle space and/or the number of active particles. Recent, quantum-information-inspired work has demonstrated that the proton and neutron sectors of a nuclear wave function are weakly entangled. Furthermore, the entanglement is smaller for nuclides away from $N=Z$, such as heavy, neutron-rich nuclides. Here we implement a weak entanglement approximation to bipartite configuration-interaction wave functions, approximating low-lying levels by coupling a relatively small number of many-proton and many-neutron states. This truncation scheme, which we present in the context of past approaches, reduces the basis dimension by many orders of magnitude while preserving essential features of nuclear spectra.