Molecular Hyperfine Interactions Research Articles

Quantum logic for trapped atoms via molecular hyperfine interactions

We study the deterministic entanglement of a pair of neutral atoms trapped in an optical lattice by coupling to excited-state molecular hyperfine potentials. Information can be encoded in the ground-state hyperfine levels and processed by bringing atoms together pairwise to perform quantum logical operations through induced electric dipole-dipole interactions. The possibility of executing both diagonal- and exchange-type entangling gates is demonstrated for two three-level atoms and a figure of merit is derived for the fidelity of entanglement. The fidelity for executing a CPHASE gate is calculated for two ${}^{87}\mathrm{Rb}$ atoms, including hyperfine structure and finite atomic localization. The main source of decoherence is spontaneous emission, which can be minimized for interaction times fast compared to the scattering rate and for sufficiently separated atomic wave packets. Additionally, coherent couplings to states outside the logical basis can be constrained by the state-dependent trapping potential.

Density functional calculations of molecular hyperfine interactions in the zero order regular approximation for relativistic effects

Expressions are derived within the relativistic regular approximation (ZORA) for the evaluation of the magnetic hyperfine interactions in paramagnetic molecules. For hydrogen-like atoms exact first order relations between the ZORA and Dirac formalism are given for the calculation of g- and A-tensors. Density functional calculations are performed on the neutral atoms Cu, Ag and Au, on some small test molecules NO2, HCO, and TiF3, and on some paramagnetic clusters consisting of 5 or 7 atoms of the group IB metals: Cu7, Cu2Ag5, CuAg6, Ag5, Ag7, and Au7. It is shown that the calculated ESR parameters of the heptamers are in good agreement with results of experiments, which originally were assigned to pentamers.

Elucidation of electronic structure by the analysis of hyperfine interactions: The MnH A 7Π–X 7Σ+ (0,0) band

We present a complete analysis of the hyperfine structure of the MnH A 7Π–X 7Σ+ (0,0) band near 5680 Å, studied with sub-Doppler resolution by intermodulated fluorescence spectroscopy. Magnetic hyperfine interactions involving both the 55Mn (I=5/2) and 1H (I=1/2) nuclear spins are observed as well as 55Mn electric quadrupole effects. The manganese Fermi contact interaction in the X 7Σ+ state is the dominant contributor to the observed hyperfine splittings; the ΔF=0, ΔN=0, ΔJ=±1 matrix elements of this interaction mix the electron spin components of the ground state quite strongly at low N, destroying the ‘‘goodness’’ of J as a quantum number and inducing rotationally forbidden, ΔJ=±2 and ±3 transitions. The hyperfine splittings of over 50 rotational transitions covering all 7 spin components of both states were analyzed and fitted by least squares, allowing the accurate determination of 14 different hyperfine parameters. Using single electronic configurations to describe the A 7Π and X 7Σ+ states and Herman–Skillman atomic radial wave functions to represent the molecular orbitals, we calculated a priori values for the 55Mn and 1H hyperfine parameters which agree closely with experiment. We show that the five high-spin coupled Mn 3d electrons do not contribute to the manganese hyperfine structure but are responsible for the observed proton magnetic dipolar couplings. Furthermore, the results suggest that the Mn 3d electrons are not significantly involved in bonding and demonstrate that the molecular hyperfine interactions may be quantitatively understood using simple physical interpretations.

Molecular hyperfine interactions in Ag(CO)3

Relativistic molecular orbital calculations in the multiple scattering approximation are reported for silver tricarbonyl, and comparisons are made to optical absorption and electron spin resonance spectra. Spin–orbit effects are modelled through the Dirac scattered-wave (DSW) formalism. Spin–polarization effects are estimated from quasirelativistic spin-unrestricted calculations. The influence of different local density potentials on the spin distributions and hyperfine tensors are examined. The calculations show good agreement with optical spectral data and with the observed 107Ag and 13C hyperfine tensors. The use of relativistic exchange–correlation potentials in calculating spin-dependent properties leads to a slightly better agreement with experiment. The calculations predict that the unpaired electron in Ag(CO)3 has about 40% silver 5pz character.

Bonding, optical, and magnetic properties of paramagnetic Ag 41+ and Ag 43+ clusters

The electronic structure of the paramagnetic Ag 4 + and Ag 4 3+ clusters is investigated by the Dirac scattered-wave method. The results show that relativistic effects are not very large, but they cannot be neglected. Due to relativity, nonnegligible 4 d–5 s hybridization arises in the bonding molecular orbitals. Spin-orbit interaction splits the occupied valence d band by 0.9 eV. Molecular hyperfine interactions (hfi) are calculated through a first-order perturbation to the Dirac Hamiltonian. The predicted hfi and excitation energies have enabled us to distinguish clearly between Ag 4 + and Ag 4 3+. The hyperfine tensors for Ag 4 + are predicted to be anisotropic, whereas those for Ag 4 3+ are mostly isotropic. The theoretical spectral assignments for Ag 4 3+ are in good agreement with recent optical and ESR studies.

MAGNETO-OPTIC AND MAGNETO-CATALYTIC EFFECT

Anticrossing and Resonance Spectroscopy provide an important amount of information on the internal processes active in chemical reactions. We investigate theoretically a simple magneto-catalytic experiment, namely ortho-para hydrogen conversion on a paramagnetic surface. In particular, we stress the importance of non-diagonal exchange interactions between the substrate and the adsorbate, in inducing optical transitions within the adsorbed H2 molecules. The state-mixing is thereafter insured by the molecular hyperfine interactions and corresponds to a double Singlet-Triplet, electronic and nuclear, mixing. The observed magnetic field effects are discussed.

Dirac scattered-wave study of trigonal bipyramidal silver clusters Ag5q+ (q=0, 2–4)

The electronic structure of the neutral and cationic pentaatomic silver bare clusters is investigated by the Dirac scattered-wave (DSW) method. The results indicate that there is significant 5s1/2–4d5/2 hybridization in the bonding molecular orbitals, due to relativistic effects. Molecular hyperfine interactions (hfi) are calculated for the paramagnetic species Agq+5 (q=0, 2, and 4) through a first-order perturbation to the Dirac Hamiltonian. The ground state (2E′) orbital degeneracy of Ag5 in D3h geometry is removed by spin-orbit interaction leading to Kramers degeneracy, and consequently the D3h geometry of Ag5 will not distort due to Jahn–Teller effect. It is found that the hyperfine coupling constants calculated by using a four-component wave function for the Ag2+5 and Ag4+5 clusters differ significantly from previously computed hfi using a second-order perturbation to the Schrödinger Hamiltonian. First ionization potentials and excitation energies are predicted for all the species as calculated by the spin-restricted transition state method.

Relativistic effects on molecular hyperfine interactions: Application to ytterbium fluorides

Dirac scattered-wave (DSW) calculations are presented for YbF3−6 and YbF5−8 clusters that model Yb+3 impurity sites in KMgF3 and CaF3 lattices, respectively. The calculations predict Γ6 and Γ7 ground states for these two cubic geometries and show good agreement with observed g tensors, spin-orbit splittings, and Yb hyperfine interactions, but overestimate the crystal field splittings and the amount of covalency between the metal and the fluorine 2p orbitals. Nevertheless, the fluorine hyperfine tensors are in qualitative agreement with experiment, and confirm the existence of a large p-orbital contribution to the isotropic part of the 19F hyperfine tensor for YbF3−6. The implications of these results for future relativistic calculations on lanthanide complexes are discussed.

Relativistic effects on molecular hyperfine interactions: Application to XeF and CsO

A relativistic theory of molecular hyperfine interactions is presented, based on the use of multiple scattering theory to generate approximate solutions to the Dirac equation. This approach should be especially useful for radicals with significant orbital contributions to the hyperfine tensor. Results for XeF and CsO are in good agreement with experiment, and show that orbital interactions are important for both heavy and light atoms, and that A⊥ for fluorine in XeF is likely to be negative.