Physics

The dissociative ionization of H + 2 in a linearly polarized, 400 nm laser pulse is simulated by solving a three-particle time-dependent Schrödinger equation in full dimensionality without using any data from quantum chemistry computation. The joint energy spectrum (JES) is computed using a time-dependent surface flux (tSurff) method, the details of which are given. The calculated ground energy is -0.597 atomic units and internuclear distance is 1.997 atomic units if the kinetic energy term of protons is excluded, consistent with the reported precise values from quantum chemistry computation. If the kinetic term of the protons is included, the ground energy is -0.592 atomic units with an internuclear distance 2.05 atomic units. Energy sharing is observed in JES and we find peak of the JES with respect to nuclear kinetic energy release (KER) is within 2∼4 eV, which is different from the previous two dimensional computations (over 10 eV), but is close to the reported experimental values. The projected energy distribution on azimuth angles shows that the electron and the protons tend to dissociate in the direction of polarization of the laser pulse.

We present a high-flux source of cold ytterbium atoms that is robust, lightweight and low-maintenance. Our apparatus delivers 10 9 atoms/s into a 3D magneto-optical trap without requiring water-cooling or high current power supplies. We achieve this by employing a Zeeman slower and a 2D magneto-optical trap fully based on permanent magnets in Halbach configurations. This strategy minimizes mechanical complexity, stray magnetic fields, and heat production while requiring little to no maintenance, making it applicable to both embedded systems that seek to minimize electrical power consumption, and large scale experiments to reduce the complexity of their subsystems.

The chemical potiential for the ground states of the atomic elements have been calculated within the semiclassical approximation The present work closely follows Schwinger and Englert's semiclassical treatment of atomic structure.

We present a measurement of the absolute frequency of the 5s 2 1 S 0 to 5s5p 3 P 0 transition in 87 Sr, which is a secondary representation of the SI second. We describe the optical lattice clock apparatus used for the measurement, and we focus in detail on how its systematic frequency shifts are evaluated with a total fractional uncertainty of 1× 10 −17 . Traceability to the International System of Units is provided via comparison to International Atomic Time (TAI). Gathering data over 5- and 15-day periods, with the lattice clock operating on average 74 % of the time, we measure the frequency of the transition to be 429228004229873.1(5) Hz, which corresponds to a fractional uncertainty of 1× 10 −15 . We describe in detail how this uncertainty arises from the intermediate steps linking the optical frequency standard, through our local time scale UTC(NPL), to an ensemble of primary and secondary frequency standards which steer TAI. The calculated absolute frequency of the transition is in good agreement with recent measurements carried out in other laboratories around the world.

We show that two-time, second-order correlations of scattered photons from planar arrays and chains of atoms display nonclassical features that can be described by a superatom picture of the canonical single-atom g 2 (τ) resonance fluorescence result. For the superatom, the single-atom linewidth is replaced by the linewidth of the underlying collective low light-intensity eigenmode. Strong light-induced dipole-dipole interactions lead to a correlated response, suppressed joint photon detection events, and dipole blockade that inhibits multiple excitations of the collective atomic state. For targeted subradiant modes, nonclassical nature of emitted light can be dramatically enhanced even compared with that of a single atom.

The preparation of large, low-entropy, highly coherent ensembles of identical quantum systems is foundational for many studies in quantum metrology, simulation, and information. Here, we realize these features by leveraging the favorable properties of tweezer-trapped alkaline-earth atoms while introducing a new, hybrid approach to tailoring optical potentials that balances scalability, high-fidelity state preparation, site-resolved readout, and preservation of atomic coherence. With this approach, we achieve trapping and optical clock excited-state lifetimes exceeding 40 seconds in ensembles of approximately 150 atoms. This leads to half-minute-scale atomic coherence on an optical clock transition, corresponding to quality factors well in excess of 10 16 . These coherence times and atom numbers reduce the effect of quantum projection noise to a level that is on par with leading atomic systems, yielding a relative fractional frequency stability of 5.2(3)× 10 −17 (τ/s ) −1/2 for synchronous clock comparisons between sub-ensembles within the tweezer array. When further combined with the microscopic control and readout available in this system, these results pave the way towards long-lived engineered entanglement on an optical clock transition in tailored atom arrays.

ARC 3.0 is a modular, object-oriented Python library combining data and algorithms to enable the calculation of a range of properties of alkali and divalent atoms. Building on the initial version of the ARC library [N. Šibalić et al, Comput. Phys. Commun. 220, 319 (2017)], which focused on Rydberg states of alkali atoms, this major upgrade introduces support for divalent atoms. It also adds new methods for working with atom-surface interactions, for modelling ultracold atoms in optical lattices and for calculating valence electron wave functions and dynamic polarisabilities. Such calculations have applications in a variety of fields, e.g., in the quantum simulation of many-body physics, in atom-based sensing of DC and AC fields (including in microwave and THz metrology) and in the development of quantum gate protocols. ARC 3.0 comes with an extensive documentation including numerous examples. Its modular structure facilitates its application to a wide range of problems in atom-based quantum technologies.

Large-scale ab initio calculations of the electric field gradient, which constitutes the electronic contribution to the electric quadrupole hyperfine constant B , were performed for the 5 s 2 5p6s 1,3 P o 1 excited states of tin, using three independent computational strategies of the variational multiconfiguration Dirac-Hartree-Fock method and a fourth approach based on the configuration interaction Dirac-Fock-Sturm theory. For the 5 s 2 5p6s 1 P o 1 state, the final value of B/Q=703(50) MHz/b differs by 0.4% from the one recently used by Yordanov et al. [Communications Physics 3 , 107 (2020)] to extract the nuclear quadrupole moments, Q , for tin isotopes in the range (117−131) Sn from collinear laser spectroscopy measurements. Efforts were made to provide a realistic theoretical uncertainty for the final B/Q value of the 5 s 2 5p6s 1 P o 1 state based on statistical principles and on correlation with the magnetic dipole hyperfine constant A .

We report multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction calculations on the Thallium (Tl) electron affinity, as well as on the excited energy levels arising from the ground configuration of Tl ??. The results are compared with the available experimental values and further validated by extending the study to its homologous, lighter element, Indium (In), belonging to Group 13 (III.A) of the periodic table. The calculated electron affinities of In and Tl, 383.4 and 322.8 meV, agree with the latest measurements by within 1\%. Three bound states 3 P 0,1,2 are confirmed in the 5 s 2 5 p 2 configuration of In ??while only the ground state 3 P 0 is bound in the 6 s 2 6 p 2 configuration of Tl ??. The isotope shifts on the In and Tl electron affinities are also estimated. The E2/M1 intraconfiguration radiative transition rates within 5 s 2 5 p 2 3 P 0,1,2 of In ??are used to calculate the radiative lifetimes of the metastable 3 P 1,2 levels.

The strong mixing of close levels with two valence electrons in Be-like xenon greatly complicates ab initio QED calculations beyond the first-order approximation. Due to a strong interplay between the electron-electron correlation and QED effects, the standard single-level perturbative QED approach may fail, even if it takes into account the second-order screened QED diagrams. In the present Letter, the corresponding obstacles are overcome by working out the QED perturbation theory for quasidegenerate states. The contributions of all the Feynman diagrams up to the second order are taken into account. The many-electron QED effects are rigorously evaluated in the framework of the extended Furry picture to all orders in the nuclear-strength parameter αZ . The higher-order electron-correlation effects are considered within the Breit approximation. The nuclear recoil effect is accounted for as well. The developed approach is applied to high-precision QED calculations of the ground and singly excited energy levels in Be-like xenon. The most accurate theoretical predictions for the binding and excitation energies are obtained. These results deviate from the most precise experimental value by 3σ but perfectly agree with a more recent measurement.