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arXiv:2404.09116

Spin entanglement of multinucleons: experimental prospects

Dong Bai, Zhongzhou Ren

Published Apr 14, 2024• 0 citations
arXivHTMLPDF

Abstract

Multiprotons and multineutrons are among the most exotic and mysterious things ever produced on earth. They provide an exceptional opportunity to understand nuclear forces and nuclear dynamics at extreme conditions, as well as neutron stars in the heaven. Quantum entanglement, referred to as ``spooky action at a distance'' by Einstein, is a ubiquitous yet deep property of quantum systems. It not only occupies a central position in quantum information science but also is investigated intensively in high energy physics, condensed matter physics, and quantum gravity. In comparison, the study of nuclear entanglement is still in infancy, and the entanglement properties of multiprotons and multineutrons in free space are generally unknown. Here, we study the crucial problem of how to measure spin entanglement of these multinucleons in nuclear experiments, with special emphases on two- and three-nucleon states. These findings open a freshly new direction for the multinucleon research. They are also useful for understanding entanglement properties of other exotic nuclear objects.

DOI
10.48550/arxiv.2404.09116

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Multiprotons and multineutrons are among the most exotic and mysterious things ever produced on earth. They provide an exceptional opportunity to understand nuclear forces and nuclear dynamics at extreme conditions, as well as neutron stars in the heaven. Quantum entanglement, referred to as ``spooky action at a distance'' by Einstein, is a ubiquitous yet deep property of quantum systems. It not only occupies a central position in quantum information science but also is investigated intensively in high energy physics, condensed matter physics, and quantum gravity. In comparison, the study of nuclear entanglement is still in infancy, and the entanglement properties of multiprotons and multineutrons in free space are generally unknown. Here, we study the crucial problem of how to measure spin entanglement of these multinucleons in nuclear experiments, with special emphases on two- and three-nucleon states. These findings open a freshly new direction for the multinucleon research. They are also useful for understanding entanglement properties of other exotic nuclear objects.
Nuclear entanglement is a flagship in the interdisciplinary direction of nuclear physics and quantum information science. Spin entanglement, a special kind of nuclear entanglement, is ubiquitous in nuclear structures and dynamics. Based on the idea of quantum state tomography, the problem of experimental determination of spin entanglement of two-nucleon pure states is studied directly within the scope of nuclear physics. It is shown that the amount of spin entanglement can be obtained by measuring three spin polarizations of one nucleon in polarization experiments. The errors from imperfect preparation of nucleon pairs are also analyzed. This work not only complements the existing literature of nuclear entanglement but also provides new opportunities for nuclear physics with polarized particles.
In this Letter, I work out spin entanglement properties of neutron-proton scattering using the exact S-matrix, considering both S-wave and higher partial wave contributions. The dependence of spin entanglement on momentum, scattering angle, and initial spin configuration is investigated for realistic nuclear forces, while low-energy properties of spin entanglement are analyzed within the framework of pionless effective field theory at leading order. New connections are found between spin entanglement and symmetry emergence of strong interactions. These results lead to a more complete understanding of how spin entanglement is generated via neutron-proton interaction. They also lay the theoretical foundation for controllable production of entangled nucleon-nucleon pairs in future experiments.
Nuclear reactions present an interesting case for studies of the time evolution of entanglement between complex quantum systems. In this work, the time-dependent nuclear density-functional theory is employed to explore entanglement in multinucleon transfer reactions. As an illustrative example, for the reaction 40Ca+208Pb^{40}\mathrm{Ca}+^{208}\mathrm{Pb}40Ca+208Pb at Elab=249MeV{E}_{\mathrm{lab}}=249\phantom{\rule{4pt}{0ex}}\mathrm{MeV}Elab​=249MeV, in the interval of impact parameters 4.65−−7.40fm4.65--7.40\phantom{\rule{4pt}{0ex}}\mathrm{fm}4.65−−7.40fm, and the relativistic density-functional PC-PK1, we compute the von Neumann entropies, entanglement between fragments, nucleon-number fluctuations, and Shannon entropy for the nucleon-number observable. A simple linear correlation is established between the entanglement and nucleon-number fluctuation of the final fragments. The entanglement between the fragments can be related to the corresponding excitation energies and angular momenta. The relationship between the von Neumann entropy and the Shannon entropy for the nucleon-number observable is analyzed, as well as the time evolution of the entanglement (nucleon-number fluctuation). The entanglement is also calculated for a range of incident energies and it is shown how, depending on the impact parameter, the entanglement increases with the collision energy.
In this work, we have been working on the concept of quantum entanglement. At first, we studied the theory of entanglement in its characterization and measurement, introducing a new scheme for detection of entanglement. The new approach links molecular-spin entities involving nuclear spins to quantum computing as more appropriate physical systems of interest. Then, we continued with the realization of entanglement in experiments. NMR has been the first choice due to its well approved advantages for quantum computing. NMR, however, has not been an appropriate system for demonstrating entangled states. Through a mathematical proof, NMR with low spin polarization has been invalidated for true implementations of non-local quantum algorithms, particularly supserdense coding. The point is that high spin polarization is inevitably required to acquire entanglement while in the current NMR it has been a formidable task to get highly polarized nuclear spins. In order to acquire high spin polarization, introducing electron spins can be much effective because of its three-order-of-magnitude larger gyromagnetic ratio compared to nuclear spins. Electron Nuclear DOuble Resonance (ENDOR) is spin manipulation technology that enables us to deal with both electron and nuclear spins. Thus, in this context, it can be more appropriate device for quantum computing. We emphasize that (pseudo)entanglement and interconversion between the entangled states have been realized with ENDOR on extremely stable organic molecular-spin entities. The required experimental conditions to obtain true quantum entanglement are also discussed. The appropriate entanglement witness for the corresponding ensemble quantum computing is introduced and examined.
We theoretically investigate quasiparticle properties of a neutron immersed in an alpha condensate, which is one of the possible states of dilute symmetric nuclear matter. The resonant ppp-wave neutron-alpha scattering, which plays a crucial role in forming halo nuclei, is considered. This system is similar to a Bose polaron near the ppp-wave Feshbach resonance that can be realized in cold-atomic experiments. Calculating the self-energy within the field-theoretical approach, we give an analytical formula for the effective mass of a polaronic neutron as a function of alpha condensation density. Moreover, two adjacent neutrons in a medium, each of which behaves like a stable polaron having an enhanced effective mass, can form a bound dineutron, with the help of 1S0^{1}S_{0}1S0​ neutron-neutron attraction. This is in contrast to the case of the vacuum, where a dineutron is known to be unbound. Our result is useful for understanding many-body physics in astrophysical environments as well as the formation of multinucleon clusters in neutron-halo nuclei.
Intensive studies of entanglement properties have proven essential for our understanding of quantum many-body systems. In contrast, much less is known about the role of quantum nonlocality in these systems because the available multipartite Bell inequalities involve correlations among many particles, which are difficult to access experimentally. We constructed multipartite Bell inequalities that involve only two-body correlations and show how they reveal the nonlocality in many-body systems relevant for nuclear and atomic physics. Our inequalities are violated by any number of parties and can be tested by measuring total spin components, opening the way to the experimental detection of many-body nonlocality, for instance with atomic ensembles.