On the long-range and short-range behavior of potentials from reproducing kernel Hilbert space interpolation

The short-range and long-range asymptotic behavior of potential functions obtained from the reciprocal power reproducing kernel Hilbert spaceinterpolation procedure [Ho and Rabitz, J. Chem. Phys. 104, 2584 (1996)] is analyzed. In the short-range region, the potential functions are polynomial in form: the method should not be used for extrapolation in this region. General formulae for the short-range and long-range expansion coefficients are presented. Potentials for He-Ar+ are discussed as examples

Magnetically tunable Feshbach resonances in Li plus Yb 3PJ

We have investigated magnetically tunable Feshbach resonances arising from the interaction of Li(2S) with metastable Yb(3P2) and(3P0). ForYb(3P2), all the resonance features are strongly suppressed by inelastic collisions that produce Yb in its lower-lying 3P1 and 3P0 states. For Yb(3P0), sharp resonances exist but they are extremely narrow (widths less than 1 mG)

Magnetic Feshbach resonances between atoms in 2^2S and 3^3P0_0 states: mechanisms and dependence on atomic properties

Magnetically tunable Feshbach resonances exist in ultracold collisions between atoms in 2 S and 3 P 0 states, such as an alkali-metal atom colliding with Yb or Sr in a clock state. We investigate the mechanisms of these resonances and identify the terms in the collision Hamiltonian responsible for them. They involve indirect coupling between the open and closed channels, via intermediate channels involving atoms in 3 P 1 states. The resonance widths are generally proportional to the square of the magnetic field and are strongly enhanced when the magnitude of the background scattering length is large. For any given pair of atoms, the scattering length can be tuned discretely by choosing different isotopes of the 3 P 0 atom. For each combination of an alkali-metal atom and either Yb or Sr, we consider the prospects of finding an isotopic combination that has both a large background scattering length and resonances at a high but experimentally accessible field. We conclude that 87 Rb + Yb , Cs + Yb , and 85 Rb + Sr are particularly promising combinations

Ultracold Li + Li₂ collisions: Bosonic and fermionic cases

We have carried out quantum dynamical calculations of vibrational quenching in Li Li2 collisions for both bosonic 7Li and fermionic 6Li. These are the first ever such calculations involving fermionic atoms. We find that for the low initial vibrational states considered here (v 3), the quenching rates are not suppressed for fermionic atoms. This contrasts with the situation found experimentally for molecules formed via Feshbach resonances in very high vibrational states

Feshbach resonances, molecular bound states, and prospects of ultracold-molecule formation in mixtures of ultracold K and Cs

We consider the possibilities for producing ultracold mixtures of K and Cs and forming KCs molecules by magnetoassociation. We carry out coupled-channel calculations of the interspecies scattering length for KCs39, KCs41, and KCs40 and characterize Feshbach resonances due to s-wave and d-wave bound states, with widths ranging from below 1 nG to 5 G. We also calculate the corresponding bound-state energies as a function of magnetic field. We give a general discussion of the combinations of intraspecies and interspecies scattering lengths needed to form low-temperature atomic mixtures and condensates and identify promising strategies for cooling and molecule formation for all three isotopic combinations of K and Cs

ArnHF van der Waals clusters revisited: II. Energetics and HF vibrational frequency shifts from diffusion Monte Carlo calculations on additive and nonadditive potential-energy surfaces for n=1-12

The ground-state energies and HF vibrational frequency shifts of ArnHF clusters have been calculated on the nonadditive potential-energysurfaces (PESs) for n=2-7 and on the pairwise-additive PESs for the clusters with n=1-12, using the diffusionMonte Carlo (DMC) method. For n>3, the calculations have been performed for the lowest-energy isomer and several higher-lying isomers which are the closest in energy. They provide information about the isomer dependence of the HF redshift, and enable direct comparison with the experimental data recently obtained in helium nanodroplets. The agreement between theory and experiment is excellent, in particular, for the nonadditive DMC redshifts. The relative, incremental redshifts are reproduced accurately even at the lower level of theory, i.e., the DMC and quantum five-dimensional (rigid Arn) calculations on the pairwise-additive PESs. The nonadditive interactions make a significant contribution to the frequency shift, on the order of 10%–12%, and have to be included in the PESs in order for the theory to yield accurate magnitude of the HF redshift. The energy gaps between the DMC ground states of the cluster isomers are very different from the energy separation of their respective minima on the PES, due to the considerable variations in the intermolecular zero-point energy of different ArnHF isomers

Atomic clock measurements of quantum scattering phase shifts spanning Feshbach resonances at ultralow fields

We use an atomic fountain clock to measure quantum scattering phase shifts precisely through a series of narrow, low-field Feshbach resonances at average collision energies below 1 μK. Our low spread in collision energy yields phase variations of order π=2 for target atoms in several F, mF states.We compare them to a theoretical model and establish the accuracy of the measurements and the theoretical uncertainties from the fitted potential.We find overall excellent agreement, with small statistically significant differences that remain unexplained

Robust storage qubits in ultracold polar molecules

Quantum states with long-lived coherence are essential for quantum computation, simulation and metrology. The nuclear spin states of ultracold molecules prepared in the singlet rovibrational ground state are an excellent candidate for encoding and storing quantum information. However, it is important to understand all sources of decoherence for these qubits, and then eliminate them, to reach the longest possible coherence times. Here we fully characterize the dominant mechanisms of decoherence for a storage qubit in an optically trapped ultracold gas of RbCs molecules using high-resolution Ramsey spectroscopy. Guided by a detailed understanding of the hyperfine structure of the molecule, we tune the magnetic field to where a pair of hyperfine states have the same magnetic moment. These states form a qubit, which is insensitive to variations in magnetic field. Our experiments reveal a subtle differential tensor light shift between the states, caused by weak mixing of rotational states. We demonstrate how this light shift can be eliminated by setting the angle between the linearly polarized trap light and the applied magnetic field to a magic angle of arccos(1/3–√)≈55∘. This leads to a coherence time exceeding 5.6 s at the 95% confidence level

Ultracold Rb-OH Collisions and Prospects for Sympathetic Cooling

We compute ab initio cross sections for cold collisions of Rb atoms with OH radicals. We predict collision rate constants of order 10-11 cm3/s at temperatures in the range 10–100 mK at which molecules have already been produced. However, we also find that in these collisions the molecules have a strong propensity for changing their internal state, which could make sympathetic cooling of OH in a Rb buffer gas problematic in magnetostatic or electrostatic traps