arXiv subjects

Zhongzhou Ren

Publications and source records attributed to Zhongzhou Ren.

At least 37 records · Page 2Linked to original sources

arXiv2024

Universal laws for nuclear contacts

The nuclear contact characterizes the nucleon-nucleon pairs in close proximity and serves as an important tool for studying the short-range correlations (SRCs) within atomic nuclei. While they have been extracted for selected nuclei, the investigation of their behavior across the nuclear chart remains limited. Very recently, Yankovich, Pazy, and Barnea have proposed a set of universal laws (YPB laws) to describe the correlation between nuclear contacts and nuclear radii and tested their laws for a small number of nuclei by using the Woods-Saxon mean-field model~[R.\ Yankovich, E.\ Pazy, and N.\ Barnea, arXiv:2407.15068 (2021)]. In this Letter, we extend their study to a majority part of the chart of nuclides within the framework of the Skyrme Hartree-Fock-Bogolyubov model, which incorporates several essential beyond-mean-field features and offers a more accurate description of the bulk properties of atomic nuclei. Our results suggest that the YPB laws hold as a good approximation for different nuclear mass regions, with minor deviations attributed to, e.g., isospin-breaking effects. Our work lays a firm foundation for future applications of the YPB laws in finite nuclei and provides new evidence for the long-range nature of the relative abundance of short-range pairs.

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arXiv2024

Nucleon thermalization hindered by isospin symmetry: Violation of eigenstate thermalization hypothesis in atomic nuclei

Bohr's compound nucleus theory is one of the most important models in nuclear physics, with far-reaching applications in nuclear science and technology. This model generally assumes that the participating nucleons attain a thermal equilibrium characterized by the microcanonical ensemble before subsequent decays. However, from a theoretical viewpoint, it remains uncertain whether this assumption is universally valid. In this Letter, we critically examine this longstanding assumption through the lens of the eigenstate thermalization hypothesis (ETH), a cornerstone of the modern quantum thermalization theory. Utilizing the time-dependent configuration interaction shell model, it is found that, in certain cases, the long-time averages of nucleon occupation numbers can exhibit significant deviations from the microcanonical ensemble averages, in contrast to the conventional expectation. We attribute this discrepancy primarily to the violation of the ETH in the presence of isospin symmetry and discover that incorporating a substantial isospin-breaking term into the shell-model Hamiltonian can effectively restore the nucleon thermalization.

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arXiv2024

Quantum computing for extracting nuclear resonances

Quantum computing has been increasingly applied in nuclear physics. In this work, we combine quantum computing with the complex scaling method to address the resonance problem. Due to the non-Hermiticity introduced by complex scaling, standard quantum computing cannot solve for complex eigenvalues directly. Therefore, it is necessary to embed the non-Hermitian operator into a larger dimensional unitary operator. Additionally, for the case of two basis vectors, we improve the traditional direct measurement method and optimize the quantum circuit. Ultimately, using the $α+α$ system as an example, we obtain the complex eigenenergies from the quantum computer that are consistent with those obtained from direct Hamiltonian diagonalization.

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arXiv2024

COLOSS: Complex-scaled Optical and couLOmb Scattering Solver

We introduce COLOSS, a program designed to address the scattering problem using a bound-state technique known as complex scaling. In this method, the oscillatory boundary conditions of the wave function are transformed into exponentially decaying ones, accommodating the long-range Coulomb interaction. The program implements the Woods-Saxon form of a realistic optical potential, with all potential parameters included in a well-designed input format for ease of use. This design offers users straightforward access to compute $S$-matrices and cross-sections of the scattering process. We provide thorough discussions on the precision of Lagrange functions and their benefits in evaluating matrix elements. Additionally, COLOSS incorporates two distinct rotation methods, making it adaptable to potentials without analytical expressions. Comparative results demonstrate that COLOSS achieves high accuracy when compared with the direct integration method, Numerov, underscoring its utility and effectiveness in scattering calculations.

physics.comp-ph↗

arXiv2024

The Hidden Variables: Harnessing Half-Shell Potentials for Enhanced Precision in Nuclear Reaction Calculations

We explore the impact of half-shell components on nuclear reaction calculations, focusing on nonelastic breakup cross sections within the Ichimura-Austern-Vincent (IAV) model. By advocating for the use of a consistent Single Folding Model (SFM) for all optical potentials in IAV calculations, we aim to reduce the uncertainties associated with half-shell components and enhance agreement with experimental data. We present results from deuteron-induced reactions on $^{60}$Ni and $^{208}$Pb, which serve as surrogate targets for neutron-induced reactions on short-lived nuclei. The application of consistent optical potentials derived from the SFM shows improved alignment with experimental data compared to traditional global phenomenological potentials. Furthermore, we investigate the $^{59}$Co($^6$Li,$αX$) reaction, which reveals that the half-shell $T$-matrix plays a pivotal role in accurately modeling nuclear reactions. Our findings suggest that a unified approach to optical potentials, accounting for half-shell effects, is critical for a precise understanding of complex nuclear reactions. This work highlights the significance of the internal dynamics of the wave function, particularly in lighter targets, and underscores the importance of the half-shell $T$-matrix as a previously underappreciated variable in reaction calculations.

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arXiv2024

Nuclear contacts of unstable nuclei

Nuclear contact is a key quantity to describe the nucleon-nucleon short-range correlations (SRCs). While they have been determined by electron scattering experiments for selected stable nuclei, nuclear contacts are largely unknown for unstable nuclei. In this work, we study nuclear contacts for a number of nuclei in the vicinity of the doubly magic $^{132}$Sn from the theoretical perspective, with special emphasis on unstable nuclei. We find that the proton-proton contact generally gets suppressed by the excess neutrons for the Sn isotopes, resembling the suppression of $α$-cluster formation reported recently for the same isotopic chain [J. Tanaka $\textit{et al}.$, Science $\textbf{371}$, 260 (2021)]. This indicates a hidden universal aspect of SRCs and $α$ clustering, two different kinds of nuclear correlations. Meanwhile, a linear relation is found between the proton-proton contact and the proton number for the $N=82$ isotones. Our results can be helpful for future experimental studies of SRCs in unstable nuclei at advanced facilities worldwide.

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arXiv2024

Evidence for Three-$α$ Breathing Modes Uncovered by Control Neural Network

This work introduces a new Control Neural Network (Ctrl.NN) method to uncover evidence of exotic quantum state, \textit{i.e.}, the breathing modes in 3-$α$ resonant states of $^{12}$C nucleus. We provide the most precise microscopic description to date for the $^{12}$C energy spectrum, identify two new exotic breathing states, and uncover strong evidence that directly connects the recent experimental observations to the breathing modes. The Ctrl.NN method significantly simplifies numerical calculations of quantum systems under multiple constraints and offers a new perspective for solving the nuclear many-body problem.

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arXiv2024

Ultrafast adiabatic passages in ultrastrongly coupled light-matter systems

We have obtained the solutions of the multimode quantum Rabi model when all modes have identical frequencies $ω$, including dark states $|ϕ_K\rangle$ with at least $K$ $(K=1,2,3,\ldots)$ photons. Extended to the multiqubit case, they lie close to another dark state $\vert ψ\rangle$ with at most one photon in the spectrum. Taking advantages of such solutions, we find a linear and symmetry-protected adiabatic passage through $\vert ψ\rangle$ to fast generate arbitrary single-photon $M$-mode $W$ states $\vert W_M\rangle$ with exactly the same speed. The effective minimum energy gap during the adiabatic evolution is further enlarged to $0.63ω$ when Stark shifts are included, such that arbitrary $\vert W_M\rangle$ can be ultrafast generated in $1.55\times 2πω^{-1}$ with fidelity $99\%$, indepedent of $M$. This work reveals the existence of linear ultrafast adiabatic passages in light-matter systems.

quant-ph↗

arXiv2024

Spin entanglement of multinucleons: experimental prospects

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.

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arXiv2023

New extended method for $ψ^{\prime}$ scaling function of inclusive electron scattering

Scaling analyses have been successfully applied to study the inclusive electron scattering $(\textit{e}, \textit{e}^{\prime})$ over the past few decades. In this paper, we utilize the $ψ^{\prime}$ scaling function in momentum space to analyze the $(\textit{e}, \textit{e}^{\prime})$ cross sections, where the nucleon momentum distributions are derived from self-consistent mean-field calculations. By further introducing the energy and momentum conservation in the scaling analysis, an improved $ψ^{\prime}$ scaling function is proposed to investigate the high-momentum part of the momentum distributions. Using the proposed scaling function, we systematically explore the effects of the nucleon-nucleon short-range correlation ($\textit{NN}$-SRC) on the $(\textit{e}, \textit{e}^{\prime})$ cross sections. From the experimental $(\textit{e}, \textit{e}^{\prime})$ data, the \textit{NN}-SRC strength is further extracted within the framework of the improved $ψ^{\prime}$ scaling function. The studies in this paper offer a new method to investigate the nucleon momentum distributions and the $\textit{NN}$-SRC effects in nuclei.

nucl-th↗

arXiv2023

Testing the validity of the surface approximation for reactions induced by weakly bound nuclei with a fully quantum-mechanical model

We examine the validity of surface approximation for breakup reactions using a fully quantum-mechanical model proposed by Ichimura, Austern, and Vincent (IAV). Analogous to the semi-classical picture, we introduce radial cut-offs to scattering waves in the IAV framework, which we refer to as IAV-cut. Systematic calculations are conducted for nonelastic breakup reactions induced by $^6$Li and deuterons at various incident energies. A comparison between the results obtained from IAV and IAV-cut is performed. The excellent agreement observed between IAV and IAV-cut in $^{6}$Li induced reactions, regardless of incident energy and target nuclei, signifies their insensitivity to the inner part of the scattering wave function, thus providing validation for the semi-classical picture. However, for deuteron induced breakup reactions, the IAV-cut results exhibit a suppression in the cross section, suggesting a strong dependence on the interior wave functions. This suppression is further enhanced as the incident energy increases.

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arXiv2022

Entanglement generation in few-nucleon scattering

Inspired by a recent Letter [S. R. Beane et al., Phys. Rev. Lett. 122, 102001(2019)], the entanglement generated in the elastic $S$-wave scattering of $p+{}^{3}\text{He}$ and $n+{}^3\text{H}$ is studied, where the proton, neutron, ${}^{3}$He, and ${}^3$H are all regarded as qubits. To deal with the Coulomb interaction between the proton and ${}^{3}$He, we derive the entanglement power, a physical quantity that measures the average entanglement generated by a scattering process, for charged qubits within the screening method. The entanglement power in the aforementioned two few-nucleon scatterings is found to be generally much smaller than that in the $S$-wave $n+p$ scattering at low energies, with the corresponding cluster effective field theories possessing an enhanced approximate $\text{SU}(2)_1\otimes\text{SU}(2)_{2}$ symmetry at leading order. Our study suggests that the entanglement generation capacities of effective interactions between nucleons and light nuclei could be more suppressed than realistic nucleon-nucleon interactions at low energies.

nucl-th↗

arXiv2022

Deterministic single-photon source in the ultrastrong coupling regime

Deterministic single-photon sources are important and ubiquitous in quantum information protocols. However, to the best of our knowledge, none of them work in the ultrastrong light-matter coupling regime, and each excitation process can only emit one photon. We propose a deterministic single-photon source in circuit QED which can work in the ultrastrong coupling regime. Here, two qubits are excited simultaneously in one process and two deterministic single photons can be sequentially emitted with an arbitrary time separation. This happens through two consecutive adiabatic transfers along the one-photon solutions of the two-qubit Rabi and Jaynes-Cummings model, which has constant eigenenergy in the whole coupling regime. Unlike the stimulated Raman adiabatic passage, the system goes back to the initial state of another period automatically after photon emission. Our scheme can approach unity single-photon efficiency, indistinguishability, and purity simultaneously. With the assistance of the Stark shift, a deterministic single photon can be generated within a time proportional to the inverse of the resonator frequency.

quant-ph↗

arXiv2022

Effects of nucleon-nucleon short-range correlations on inclusive electron scattering

The nucleon-nucleon short-range correlation NN-SRC is one of the key issues of nuclear physics, which typically manifest themselves in high-momentum components of the nuclear momentum distributions. In this letter, the nuclear spectral functions based on the axially deformed relativistic mean-field model are developed to involve the NN-SRC. With the spectral functions, the inclusive electron scattering $ (e,e^{\prime}) $ cross sections are calculated within the PWIA framework, including the quasi-elastic (QE) part and $ Δ$ production part. Especially in the $ Δ$ production region, we reconsider the electromagnetic structures of the nucleon resonance $ Δ$(1232) and the scattering mechanisms, thereby the theoretical calculations are improved effectively and the cross sections are well consistent with the experimental data. The theoretical $ (e,e^{\prime}) $ cross sections are further divided into NN-SRC and mean-field contributions. It is found that, at the kinematics $ 0.5 \,{\rm GeV}^{2}<Q^{2}<1 \,{\rm GeV}^{2} $, the QE peak and $ Δ$ production peak not only reflect the mean-field structure, but also are sensitive to the NN-SRC information. Finally, we provide a new method to extract the strengths of NN-SRC from experimental cross sections for selected nuclei at the suitable kinematics.

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arXiv2022

Exploring sensitivity of charge-exchange ($p, n$) reactions to the neutron density distribution

$Background:$ The determination of the nuclear neutron properties suffers from uncontrolled uncertainties, which attracted considerable attention recently, such as in the context of the PREX experiment. $Purpose:$ Our aim is to analyze the sensitivity of charge-exchange ($p, n$) reactions to the neutron density distribution $ρ_{n}$ and constrain the neutron characteristics in the nuclear structure models. $Method:$ By combing the folding and the mean-field models, the nucleon-nucleus ($NA$) potential can be obtained from the nuclear density distribution. Further, the ($p, p$) and ($p, n$) cross sections for $^{48}$Ca and $^{208}$Pb are calculated following the distorted-wave Born approximation (DWBA) method. $Results:$ Compared with the ($p, p$) cross section, the effects of $ρ_{n}$ variation on the ($p, n$) cross section are significant, which is due to the impact of isovector properties. Based on the global folding model analyses of data, it is found that $^{48}$Ca and $^{208}$Pb have relatively large neutron skin thickness $ΔR_{n p}$. $Conclusions:$ Results illustrate that the charge-exchange ($p, n$) reaction is a sensitive probe of $ρ_{n}$. The results in this paper can offer useful guides for future experiments of neutron characteristics.

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arXiv2021

Extraction of the second and fourth radial moments of nuclear charge density from the elastic electron-nucleus scattering

The expression for the radial moments $\left\langle r^{n}\right\rangle_{c}$ of the nuclear charge density has been discussed under the plane wave Born approximation (PWBA) method recently, which is significant to investigate the nuclear surface thickness and neutron distribution radius. In this paper, we extend the studies of extracting second-order moment $\left\langle r^{2}\right\rangle_{c}$ and fourth-order moment $\left\langle r^{4}\right\rangle_{c}$ from the Coulomb form factors $|F_{C}(q)|^2$ by the distorted wave Born approximation (DWBA) at the small momentum transfer $ q $ region. Based on the relativistic mean-field (RMF) calculations, the DWBA form factors $F_{C}^{DW}(q)$ are expanded into $ q^4 $, where the corresponding charge distributions are corrected by the contributions of neutron and spin-orbit densities. In the small $ q $ region, it is found that the experimental $|F_{C}(q)|^2$ can be well reproduced by considering the contributions of the $\left\langle r^{4}\right\rangle_{c}$ at the small $ q $ region. Through further analyzing the second-order and fourth-order expansion coefficients of the $F_{C}^{DW}(q)$, the relationship between the expansion coefficients and proton number $ Z $ is obtained. By the relationship, we extract the $\left\langle r^{2}\right\rangle_{c}$ and $\left\langle r^{4}\right\rangle_{c}$ from the limited experimental data of form factors at the small $ q $ region. Within the permissible range of error, the extracted $\left\langle r^{n}\right\rangle_{c}$ are consistent with the experimental data in this paper.

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arXiv2021

Nucleon momentum distribution of $^{56}\text{Fe}$ from the axially deformed relativistic mean-field model with nucleon--nucleon correlations

Nucleon momentum distribution (NMD), particularly its high-momentum components, is essential for understanding the nucleon--nucleon ($ NN $) correlations in nuclei. Herein, we develop the studies of NMD of $^{56}\text{Fe}$ from the axially deformed relativistic mean-field (RMF) model. Moreover, we introduce the effects of $ NN $ correlation into the RMF model from phenomenological models based on deuteron and nuclear matter. For the region $ k k_{\text{F}} $, the high-momentum components of the RMF model are modified by the effects of $ NN $ correlation, which agree with the experimental data. Comparing the NMD of relativistic and non-relativistic mean-field models, the relativistic effects on nuclear structures in momentum space are analyzed. Finally, by analogizing the tensor correlations in deuteron and Jastrow-type correlations in nuclear matter, the behaviors and contributions of $ NN $ correlations in $^{56}\text{Fe}$ are further analyzed, which helps clarify the effects of the tensor force on the NMD of heavy nuclei.

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arXiv2021

$α$-cluster structures above double shell closures via double-folding potentials from chiral effective field theory

$α$-cluster structures above double shell closures are among the cornerstones for nuclear $α$-cluster physics. Semi-microscopic cluster models (SMCMs) are important theoretical models to study their properties. A crucial ingredient of SMCM is the effective potential between the alpha cluster and the doubly magic nucleus. We derive new double-folding potentials between $α$ clusters and doubly magic nuclei from soft local chiral nucleon-nucleon potentials given by chiral effective field theory ($χ$EFT) at the next-to-next-to-leading order. The $α$-cluster structures in ${}^{8}\text{Be}$, ${}^{20}\text{Ne}$, ${}^{44,52}\text{Ti}$, and ${}^{212}\text{Po}$ are explored to validate these new double-folding potentials. The $α$ decay of ${}^{104}\text{Te}$ is also studied in the light of recent experimental results. Our study shows that double-folding potentials from $χ$EFT are the new reliable effective potentials for the SMCM approach to $α$-cluster structures above double shell closures, with both conceptual and phenomenological merits.

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