Windows on the Universe: Open Quantum Systems in Atomic Nuclei at FRIB

This proposal seeks to understand how protons and neutrons interact when they are placed in an environment where there are far more neutrons than protons, also known as rare isotopes. These neutron-rich rare isotopes straddle the limit of existence, which defines the neutron drip line, where protons and neutrons no longer form a nucleus because they do not “stick” together (e.g., become unbound). They offer an opportunity to explore the unique science of systems that interact with themselves, also referred to as open quantum systems. This research will be conducted at worldwide scientific user facilities, and primarily at the Facility for Rare Isotope Beams in Michigan that is estimated to produce nearly 1,000 new isotopes in this region of interest. The structure and properties of these isotopes are highly relevant for understanding astrophysical processes. In addition, this topic has special significance due to its relevance to quantum computing, quantum optics, and quantum sensing. A part of the research that will be performed involves the MoNA Collaboration, which consists of a group of undergraduate institutions that has had a major impact on recruitment of students to enter nuclear science. The research will further develop the LISE++ code that is used by thousands of scientists around the world for the modeling of rare isotope production. This proposal is to perform experimental studies of weakly bound atomic nuclei in order to test nuclear models that are relevant to understanding open quantum systems and astrophysical processes in the universe. Proper modeling and understanding of continuum effects are important in the era of multi-messenger astronomy where nuclear properties, such as binding energies and nuclear radii are relevant for interpreting optical, neutrino, and gravitational-wave observations. It will address fundamental questions, such as what combination of neutrons and protons can form an atomic nucleus and perhaps double our knowledge of the neutron drip line. Properties of unbound states will be measured using the powerful tools of the MoNA Collaboration and the wide range of new nuclei accessible at FRIB. New techniques will be developed to exploit quasi-elastic proton removal reactions to probe states near the particle emission threshold and the structure of weakly-bound nuclei, including the characterization of near threshold resonances in loosely bound systems. Finally, due to the open-quantum nature of the states of interest, the reaction mechanism to produce these states becomes an important part of the measurement. The role of the reaction mechanism in the context of open quantum systems will be explored with the development of dedicated equipment (e.g., Cherenkov and Rutherford scattering based detectors). This project advances the objectives of "Windows on the Universe: the Era of Multi-Messenger Astrophysics", one of the 10 Big Ideas for Future NSF Investments. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.