Session U04: Theory & Experiment: Spectroscopy Lifetimes & Oscillator Strengths

Doppler-Free EIT Measurements of Isotope Shifts and Hyperfine Structure of the Potassium-41 6s State

We report Doppler-free measurements and theoretical modeling of the 4s_1/2-4p_1/2-6s_1/2 ladder using electromagnetically induced transparency (EIT).  Using the acquired spectra we have measured the hyperfine splittings and isotope shift of the 6s state of potassium 41, which has not previously been reported.  In the experiments the probe laser is locked to the to one of the 4s_1/2-4p_1/2 hyperfine transitions, while the coupling laser is scanned over the 4p_1/2-6s_1/2 transition. EIT was measured in a magnetically shielded warm vapor cell. The spectra are complicated by the relatively small hyperfine splitting in the 4p_1/2 state. We have explored the effect of relative polarizations of the probe and coupling lasers on the spectra both experimentally and with a multi-level theoretical model including magnetic sublevels.   

Four-level, all infrared, Doppler-free Rydberg EIT in rubidium

Four-level, three-photon ladder Rydberg EIT has several potential advantages over the more popular two-photon Rydberg EIT in its applications to field sensing and non-classical photon state generation. For example, in warm vapors, Doppler-free alignments leading to zero-velocity spin waves or expanded velocity class inclusion are possible with three-photon EIT. We present experiments in warm vapors using an all-infrared scheme which include collinear configurations of the incoming lasers and a Doppler-free configuration where the incoming beams’ wavevectors sum vectorially to zero. We show that numerical simulations match the qualitative features of the experimental configurations and that there are regimes where the Doppler-free configuration may lead to improved sensitivity over collinear configurations.   

Solving for many-body stationary states using the Geminal Density Matrix

The ground state energy of an arbitrary many-electron system can be calculated by minimizing its total energy as a functional of the two-body reduced density matrix (2-RDM). Such a minimization yields exact results only if the 2-RDM is sufficiently constrained so that it corresponds to a valid many-body wave function. Despite significant progress over the last few decades, a complete set of these so-called N-representability constraints has not been determined. This work approaches the problem by expanding the 2-RDM in a complete set of two-electron eigenstates and analyzing the matrix formed by the expansion coefficients. This matrix, which we call the geminal density matrix (GDM), is found to evolve unitarily in time by the Liouville-Von Neumann equation. By studying the time evolution induced by a Hamiltonian that slowly switches on the Coulomb interaction, we show by the adiabatic theorem that matrices representing eigenstates of a non-interacting system can be evolved into those for a system with electron-electron interactions in a manner which preserves N-representability.

    

Long-Range Rydberg States of Sr2+

Long-range diatomic Rydberg molecules with charged atomic cores have potential application in quantum computing, and there has recently been considerable interest in these types of systems. In this work, high-lying long-range Rydberg states of spin-polarized Sr₂⁺ are presented. The electronic spectra were computed using an analytical approach involving a local frame transformation developed in a previous work, in which a scattering K-matrix for collisions of the Rydberg electron with the charged cores is determined from states of H₂⁺ and experimental quantum defects for Sr. A formalism for determining dipole matrix elements between high-lying states of Sr₂⁺ and the 5s5p state of Sr is presented. This formalism assumes the Sr atoms are each trapped in an optical tweezer, with a normal mode analysis used to compute the rovibrational overlap integral. Some bound states of Sr₂⁺ in this regime that could be experimentally observed are identified.   

Further developments in a parallel configuration interaction code for applications on complex systems

We have continued the development of our new parallel atomic structure codes, improving the methods of constructing matrices. Our configuration interaction code now features a dynamic workload distribution method to form the Hamiltonian matrix, proving to be much more scalable than the previous static version. This allows for much more efficient use of many processors. The Davidson procedure has also been improved to allow a larger initial approximation to be considered in negligible time. We report the application of our codes to the calculation of the oscillator-strength ratio of two Fe XVII transitions, which has recently been shown to finally agree with experiments (arXiv:2201.09070).    

Precision calculation of hyperfine constants for extracting nuclear moments of 229Th.

Determination of nuclear moments for many nuclei relies on the computation of hyperfine constants, with theoretical uncertainties directly affecting the resulting uncertainties of the nuclear moments. In this work, we improve the precision of such a method by including for the first time an iterative solution of equations for the core triple cluster amplitudes into the relativistic coupled-cluster method, with large-scale complete basis sets. We carried out calculations of the energies and magnetic dipole and electric quadrupole hyperfine structure constants for the low-lying states of ²²⁹Th³⁺ in the framework of such relativistic coupled-cluster single double triple (CCSDT) method. We present a detailed study of

various corrections to all calculated properties. Using the theory results and experimental data we found the nuclear magnetic dipole and electric quadrupole moments to be

μ = 0.366(6) μ_N and Q = 3.11(2) eb and reducing the uncertainty of the quadrupole moment by a factor of three. The Bohr-Weisskopf effect of the finite nuclear magnetization is investigated, with bounds placed on the deviation of the magnetization distribution from the uniform one.   

Fock-space relativistic coupled-cluster calculation of the clock properties in two-valence Al+ ion.

The recent advances in the development of new and improved frequency and time standards in optical domain provides a road map to study fundamental as well as technological applications. To mention some important applications, probing physics beyond the standard model of particle physics, searching for the variation in the fundamental constants, navigation systems, and the basis for the redefinition of the second [1 - 4]. The group-13 ions are identified as the promising candidates for the accurate optical clocks as they are expected to have a low fractional frequency shift [5,6]. For example, the fractional frequency shift for ¹S₀ – ³P₀ clock transition in Al⁺ is reported to be 9.4×10^-19 [7]. Since the direct measurement of black-body radiation shift is nontrivial, the accurate data from high precision atomic structure calculations are important in developing the new optical frequency standards. Considering the two-valence nature of Al⁺, accurate calculation of the properties, however, requires the inclusion of electron correlation effects to the highest level of accuracy.

In this work, we have developed a Fock-space relativistic coupled-cluster theory based method for the properties calculation of two-valence atoms and ions. We have then employed this method to compute the excitation energies, hyperfine structure constants, oscillator strength, and the lifetime of the ³P^o₀ clock state for Al⁺ ion [8].

References

[1] S. G. Karshenboim and E Peik, Astro., Clocks and Fundamental Const, (Springer, NewYork, 2010).

[2] M. S. Grewal, et al. Global Navigation Satellite Systems, Inertial Navig, and Int. (Wiley, New York, 2013).

[3] M. S. Safronova, et al. Rev. Mod. Phys. 90, 025008 (2018).

[4] F. Riehle, et al. Metrologia 55, 188 (2018).

[5] M. S. Safronova, et al. Phys. Rev. Lett. 107, 143006 (2011).

[6] Z. Zuhrianda, et al. Phys. Rev. A 85, 022513 (2012).

[7] S. M. Brewer, et al. Phys. Rev. Lett. 123, 033201 (2019).

[8] Ravi Kumar, et al. Phys. Rev. A 103, 022801 (2021).   

Comprehensive calculations of energy levels, radiative transition parameters, hyperfine structure constants AJ - BJ, Landé gJ factors and isotope shifts for Sc XX

Atomic parameters are crucial for calculating stellar opacities, chemical abundance, developing sophisticated stellar atmosphere models, plasma diagnosis and modelling. Isotope shifts (IS) and hyperfine structures (HFS) are essential for precise and correct spectra analysis. Recently, studies on scandium have become an exquisite research topic as its energy levels, transition rates, weighted oscillator strengths, HFS are needed for the accurate study of nucleosynthesis processes, abundance anomalies in stars and plasma diagnosis. Sc is usually present in its ionic form in high-temperature plasma, and He-like ions have dominant features in X-ray spectra of stars. Therefore we carry out large scale calculations of the energy levels, transition rates for multipole transitions, lifetimes, HFS constants, Landé g_J factors, and IS factors for the lowest 127 levels of Sc XX using the multi-configurational Dirac–Fock procedure. GRASP2018 and RIS4 packages are used to perform the computation. The leading quantum electrodynamic corrections, Breit interaction, nuclear recoil effects and electron correlation effects on the atomic structures are also studied. An excellent agreement with the previously available results is observed. A large section of the results is reported for the first time.   

Relativistic perturbation-theory calculations for actinide atoms and ions

Actinide atoms and ions present challenges to atomic theory calculations due to a large number of electrons and their complicated interactions. Conventional approaches such as calculations based on Cowan’s code are limited and require a large number of parameters for energy agreement. One promising approach is relativistic configuration-interaction and many-body perturbation theory (CI-MBPT) methods. We will present CI-MBPT results for various uranium and plutonium atoms and ions. Among atomic properties, energies, g-factors, electric dipole moments, lifetimes, hyperfine structure constants, and isotopic shifts will be discussed. While some progress is made, more work is needed for better understanding these challenging atomic systems.

    

A Science Gateway for Atomic, Molecular and Optical Science(AMOS): Democratizing AMOS Research and Education

A group of internationally known atomic and molecular theorists are developing a computational portal (amosgateway.org) where practitioners can access a synergistic, full-scope platform for computational Atomic, Molecular, and Optical Science (AMOS). The AMOSGateway currently hosts eleven state-of-the-art AMOS software suites and is powered by an advanced cyberinfrastructure (CI) enabling a flexible and easy-to-use platform for the broad AMOS community. The gateway-hosted AMOS applications are best-of-breed approaches for computing atomic spectra, transition probabilities, electron collision/photoionization processes, including the control of atomic and molecular systems by laser-atom/molecule interactions. The AMOS scientific group is complemented by experts in CI and computational science capable of delivering advanced CI and high-performance computing integration expertise.  The developers also deliver new capabilities to scientists interested in applications of AMOS data, and to researchers and educators who are not computational AMO scientists. The applications are directly accessed on the gateway, where they been compiled on a number of NSF compute systems.  Users are able to access and modify input files for their own purposes and then submit them for execution on one of the NSF systems using the XSEDE AMOSGateway account.

We will discuss how the gateway operates by accessing the platform, and if time permits, launching a simple job, and displaying typical output.  A description of work in progress to make the platform more transparent for use by non-experts and an outlook to the future will also be given.