Atomic Physics

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BOUND and FIELD: programs for calculating bound states of interacting pairs of atoms and molecules (1811.09111v2)

Jeremy M. Hutson, C. Ruth Le Sueur

2018-11-22

The BOUND program calculates the bound states of a complex formed from two interacting particles using coupled-channel methods. It is particularly suitable for the bound states of atom-molecule and molecule-molecule Van der Waals complexes and for the near-threshold bound states that are important in ultracold physics. It uses a basis set for all degrees of freedom except , the separation of the centres of mass of the two particles. The Schr"odinger equation is expressed as a set of coupled equations in . Solutions of the coupled equations are propagated outwards from the classically forbidden region at short range and inwards from the classically forbidden region at long range, and matched at a point in the central region. Built-in coupling cases include atom + rigid linear molecule, atom + vibrating diatom, atom + rigid symmetric top, atom + asymmetric or spherical top, rigid diatom + rigid diatom, and rigid diatom + asymmetric top. Both programs provide an interface for plug-in routines to specify coupling cases (Hamiltonians and basis sets) that are not built in. With appropriate plug-in routines, BOUND can take account of the effects of external electric, magnetic and electromagnetic fields, locating bound-state energies at fixed values of the fields. The related program FIELD uses the same plug-in routines and locates values of the fields where bound states exist at a specified energy. As a special case, it can locate values of the external field where bound states cross scattering thresholds and produce zero-energy Feshbach resonances. Plug-in routines are supplied to handle the bound states of a pair of alkali-metal atoms with hyperfine structure in an applied magnetic field.

MOLSCAT: a program for non-reactive quantum scattering calculations on atomic and molecular collisions (1811.09584v2)

Jeremy M. Hutson, C. Ruth Le Sueur

2018-11-23

MOLSCAT is a general-purpose program for quantum-mechanical calculations on nonreactive atom-atom, atom-molecule and molecule-molecule collisions. It constructs the coupled-channel equations of atomic and molecular scattering theory, and solves them by propagating the wavefunction or log-derivative matrix outwards from short range to the asymptotic region. It then applies scattering boundary conditions to extract the scattering matrix (S matrix). Built-in coupling cases include atom + rigid linear molecule, atom + vibrating diatom, atom + rigid symmetric top, atom + asymmetric or spherical top, rigid diatom + rigid diatom, rigid diatom + asymmetric top, and diffractive scattering of an atom from a crystal surface. Interaction potentials may be specified either in program input (for simple cases) or with user-supplied routines. For the built-in coupling cases, MOLSCAT can loop over partial wave (or total angular momentum) to calculate elastic and inelastic cross integral sections and spectroscopic line-shape cross sections. Post-processors are available to calculate differential cross sections, transport, relaxation and Senftleben-Beenakker cross sections, and to fit the parameters of scattering resonances. MOLSCAT also provides an interface for plug-in routines to specify coupling cases (Hamiltonians and basis sets) that are not built in; plug-in routines are supplied to handle collisions of a pair of alkali-metal atoms with hyperfine structure in an applied magnetic field. For low-energy scattering, MOLSCAT can calculate scattering lengths and effective ranges and can locate and characterize scattering resonances as a function of an external variable such as the magnetic field.

Raman sideband cooling of a single atom in an optical dipole trap: Towards theoretical optimum in a three-dimensional regime (1903.05897v1)

V. M. Porozova, L. V. Gerasimov, I. B. Bobrov, S. S. Straupe, S. P. Kulik, D. V. Kupriyanov

2019-03-14

We clarify the optimal conditions for the protocol of Raman sideband cooling (RSC) of a single atom confined with a tightly focused far-off-resonant optical dipole trap (optical tweezers). The protocol ultimately pursues cooling to a three-dimensional ground state of the confining potential. We show that the RSC protocol has to fulfil a set of critical requirements for the parameters of cooling beams and the excitation geometry to be effective in a most general three-dimensional confguration and for an atom, having initial temperature between the recoil and the Doppler bounds. We perform a numerical simulation of the Raman passage for an example of an Rb atom taking into account the full level structure and all possible transition channels.

Particle-particle ladder based basis-set corrections applied to atoms and molecules using coupled-cluster theory (1903.05559v2)

Andreas Irmler, Andreas Grüneis

2019-03-13

We investigate the basis-set convergence of coupled cluster electronic correlation energies using a recently proposed finite basis-set correction technique. The correction is applied to atomic and molecular systems and is based on a diagrammatically decomposed coupled cluster singles and doubles correlation energy. Only the second-order energy and the particle-particle ladder term are corrected for their basis-set incompleteness error. We present absolute correlation energies for the HO and F molecules. Furthermore atomization energies for a test set containing 49 molecules are investigated and the performance of the employed basis-set correction technique is compared to explicitly correlated methods. Our findings indicate that it is possible to achieve basis-set reductions that are comparable to state-of-the-art F12 theories. The employed technique can readily be transfered to other many-electron wavefunction methods without the need for three- and four-electron integrals.

Electric dipole polarizability of group-IIIA ions using PRCC: Large correlation effects from nonlinear terms (1903.05829v1)

Ravi Kumar, S. Chattopadhyay, B. K. Mani, D. Angom

2019-03-14

We compute the ground-state electric dipole polarizability of group-IIIA ions using the perturbed relativistic coupled-cluster (PRCC) theory. To account for the relativistic effects and QED corrections, we use the Dirac-Coulomb-Breit Hamiltonian with the corrections from the Uehling potential and the self-energy. The effects of triple excitations are considered perturbatively in the PRCC. Our PRCC results for are good in agreement with the previous theoretical results for all the ions. From our computations we find that the nonlinear terms in PRCC have significant contributions and must be included to obtain the accurate value of for group-IIIA ions. For the correction from the Breit interaction, we find that it is largest for Al and decreases as we go towards the heavier ions. The corrections from the vacuum polarization and the self-energy increase from lighter to heavier ions.

Coherent Control of the Rotational Degree of Freedom of a Two-Ion Coulomb Crystal (1903.05763v1)

Erik Urban, Neil Glikin, Sara Mouradian, Kai Krimmel, Boerge Hemmerling, Hartmut Haeffner

2019-03-13

We demonstrate the preparation and coherent control of the angular momentum state of a two-ion crystal. The ions are prepared with an average angular momentum of freely rotating at 100~kHz in a circularly symmetric potential, allowing us to address rotational sidebands. By coherently exciting these motional sidebands, we create superpositions of states separated by up to four angular momentum quanta. Ramsey experiments show the expected dephasing of the superposition which is dependent on the number of quanta separating the states. These results demonstrate coherent control of a collective motional state described as a quantum rotor in trapped ions. Moreover, our work offers an expansion of the utility of trapped ions for quantum simulation, interferometry, and sensing.

H-, He-like recombination spectra III: -changing collisions in highly-excited Rydberg states and their impact on the radio, IR and optical recombination lines (1903.05730v1)

F. Guzmán, M. Chatzikos, P. A. M. van Hoof, Dana S. Balser, M. Dehghanian, N. R. Badnell, G. J. Ferland

2019-03-13

At intermediate to high densities, electron (de-)excitation collisions are the dominant process for populating or depopulating high Rydberg states. In particular, the accurate knowledge of the energy changing (-changing) collisional rates is determinant for predicting the radio recombination spectra of gaseous nebula. The different datasets present in the literature come either from impact parameter calculations or semi-empirical fits and the rate coefficients agree within a factor of two. We show in this paper that these uncertainties cause errors lower than 5% in the emission of radio recombination lines (RRL) of most ionized plasmas of typical nebulae. However, in special circumstances where the transitions between Rydberg levels are amplified by maser effects, the errors can increase up to 20%. We present simulations of the optical depth and H line emission of Active Galactic Nuclei (AGN) Broad Line Regions (BLRs) and the Orion Nebula Blister to showcase our findings.

All the Fun of the FAIR: Fundamental physics at the Facility for Antiproton and Ion Research (1903.05693v1)

M. Durante, P. Indelicato, B. Jonson, V. Koch, K. Langanke, Ulf-G. Meißner, E. Nappi, T. Nilsson, Th. Stöhlker, E. Widmann, M. Wiescher

2019-03-13

The Facility for Antiproton and Ion Research (FAIR) will be the accelerator-based flagship research facility in many basic sciences and their applications in Europe for the coming decades. FAIR will open up unprecedented research opportunities in hadron and nuclear physics, in atomic physics and nuclear astrophysics as well as in applied sciences like materials research, plasma physics and radiation biophysics with applications towards novel medical treatments and space science. FAIR is currently under construction as an international facility at the campus of the GSI Helmholtzzentrum for Heavy-Ion Research in Darmstadt, Germany. While the full science potential of FAIR can only be harvested once the new suite of accelerators and storage rings is completed and operational, some of the experimental detectors and instrumentation are already available and will be used starting in summer 2018 in a dedicated research program at GSI, exploiting also the significantly upgraded GSI accelerator chain. The current manuscript summarizes how FAIR will advance our knowledge in various research fields ranging from a deeper understanding of the fundamental interactions and symmetries in Nature to a better understanding of the evolution of the Universe and the objects within.

Angle-resolved photoemission spectroscopy of a Fermi-Hubbard system (1903.05678v1)

Peter T. Brown, Elmer Guardado-Sanchez, Benjamin M. Spar, Edwin W. Huang, Thomas P. Devereaux, Waseem S. Bakr

2019-03-13

Angle-resolved photoemission spectroscopy (ARPES) measures the single-particle excitations of a many-body quantum system with both energy and momentum resolution, providing detailed information about strongly interacting materials. ARPES is a direct probe of fermion pairing, and hence a natural technique to study the development of superconductivity in a variety of experimental systems ranging from high temperature superconductors to unitary Fermi gases. In these systems a remnant gap-like feature persists in the normal state, which is referred to as a pseudogap. A quantitative understanding of pseudogap regimes may elucidate details about the pairing mechanisms that lead to superconductivity, but developing this is difficult in real materials partly because the microscopic Hamiltonian is not known. Here we report on the development of ARPES to study strongly interacting fermions in an optical lattice using a quantum gas microscope. We benchmark the technique by measuring the occupied single-particle spectral function of an attractive Fermi-Hubbard system across the BCS-BEC crossover and comparing to quantum Monte Carlo calculations. We find evidence for a pseudogap in our system that opens well above the expected critical temperature for superfluidity. This technique may also be applied to the doped repulsive Hubbard model which is expected to exhibit a pseudogap at temperatures close to those achieved in recent experiments.

Estimation of antihydrogen properties in experiments with small signal deficit (1809.10392v2)

Balint Radics

2018-09-27

For a class of precision CPT-invariance test measurements using antihydrogen, a deficit in the data indicates the presence of the signal. The construction of classical confidence intervals for the properties of the antiatoms from measurements may pose a challenge due to the limited statistics experimentally available. We use the Feldman-Cousins method to estimate model parameters for such a low count rate measurement. First, we construct confidence intervals for the Poisson process with a known background and an unknown signal deficit. Then the generalized Monte Carlo version of the method is applied to the use case of the hyperfine transition frequency measurement of the ground-state antihydrogen atom, where the expected double-dip resonance line shape and the mean background is assumed to be known. We find that confidence intervals of the antihydrogen properties could be obtained already from low statistics data. We also discuss how the method may be extended to allow estimation of additional model parameters.

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