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Nuclear Theory·nucl-th

Wednesday·September 20, 2023

8 papers—4 primary·4 cross-listed

All8Primary4Cross-lists4
  1. 05

    [Submitted on 1 Sept 2023] (cross-list from quant-ph)

    Nuclear Spectra from Quantum Lanczos Algorithm with Real-Time Evolution and Multiple Reference States

    Amanda Bowman🇺🇸

    Models of quantum systems scale exponentially with the addition of single-particle states, which can present computationally intractable problems. Alternatively, quantum computers can store a many-body basis of dimensions on qubits. This motivated the quantum eigensolver algorithms developed in recent years, such as the quantum Lanczos algorithm based on the classical, iterative Lanczos algorithm. I performed numerical simulations to find the low-lying eigenstates of Ne, Na, and Na to compare imaginary- and real-time evolution. Though imaginary-time evolution leads to faster convergence, real-time evolution still converges within tens of iterations and satisfies the requirement for unitary operators on quantum computers. Additionally, using multiple reference states leads to faster convergences or higher accuracy for a fixed number of real-time iterations. I performed quantum circuit prototype numerical simulations on a classical computer of the QLanczos algorithm with real-time evolution and multiple reference states to find the low-lying eigenstates of Be. These simulations were run in both the spherical basis and Hartree-Fock basis, demonstrating that an M-scheme spherical basis leads to lower depth circuits than the Hartree-Fock basis. Finally, I present the quantum circuits for the QLanczos algorithm with real-time evolution and multiple references.

    Comments:
    62 pages, 19 figures
    Subjects:
    Quantum Physics (quant-ph); Nuclear Theory (nucl-th)
    arXiv:
    2309.00759 [pdf]
    0 citations
  2. 06

    [Submitted on 18 Sept 2023] (cross-list from nucl-ex)

    Status of experimental knowledge on the unbound nucleus Be

    K.L. Jones · J. Kovoor · R. Kanungo

    The structure of the unbound nucleus Be is important to understanding the Borromean, two-neutron halo nucleus Be. The experimental studies conducted over the last four decades are reviewed in the context of the beryllium chain of isotopes and some significant theoretical studies. One focus of this paper is the comparison of new data from a Be(d,p) reaction in inverse kinematics, which was analyzed using GEANT4 simulations and a Bayesian fitting procedure, with previous measurements. Two possible scenarios to explain the strength below 1~MeV above the neutron separation energy were proposed in that study: a single -wave resonance, or a mixture of an -wave virtual state with a weaker either -wave or -wave resonance. Comparisons of recent invariant mass and the (d,p) experiments show good agreement between the transfer measurement and the two most recent high-energy nucleon removal measurements.

    Comments:
    10 pages 2 figures
    Subjects:
    Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    2309.10086 [pdf]
    Front.in Phys.(2023)·2 citations
  3. 07

    [Submitted on 19 Sept 2023] (cross-list from cond-mat.quant-gas)

    Thermodynamics of spin-1/2 fermions on coarse temporal lattices using automated algebra

    K. J. Morrell · A. J. Czejdo · N. Carter · J. E. Drut

    Recent advances in automated algebra for dilute Fermi gases in the virial expansion, where coarse temporal lattices were found advantageous, motivate the study of more general computational schemes that could be applied to arbitrary densities, beyond the dilute limit where the virial expansion is physically reasonable. We propose here such an approach by developing what we call the Quantum Thermodynamics Computational Engine (QTCE). In QTCE, the imaginary-time direction is discretized and the interaction is accounted for via a quantum cumulant expansion, where the coefficients are expressed in terms of noninteracting expectation values. The aim of QTCE is to enable the systematic resolution of interaction effects at fixed temporal discretization, as in lattice Monte Carlo calculations, but here in an algebraic rather than numerical fashion. Using this approach, in combination with numerical integration techniques (both known and alternative ones proposed here), we explore the thermodynamics of spin-1/2 fermions, focusing on the unitary limit in 3 spatial dimensions, but also exploring the effects of continuously varying the spatial dimension below 3. We find that, remarkably, extremely coarse temporal lattices, when suitably renormalized using known results from the virial expansion, yield stable partial sums for QTCE's cumulant expansion which are qualitatively and quantitatively correct in wide regions, compared with known experimental results.

    Comments:
    11 pages, 11 figures
    Subjects:
    Quantum Gases (cond-mat.quant-gas); Nuclear Theory (nucl-th)
    arXiv:
    2309.10222 [pdf]
    Phil.Trans.Roy.Soc.Lond.A(2024)·1 citation
  4. 08

    [Submitted on 19 Sept 2023] (cross-list from nucl-ex)

    K Isomers in Transuranium Nuclei

    Fritz Peter Heßberger

    K isomers in transuranium nuclei have become a most interesting subject in nuclear structure investigation in many laboratories within the recent twenty years. In this paper an overview on the present day situation will be given. It will focus on the conditions for occuring of this kind of isomers, their decay properties and systematics in their properties as far as experimental data are available.

    Subjects:
    Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    2309.10468 [pdf]
    7 citations

Affiliations

first authorsco-authorsvia INSPIRE