Physics and Astronomy Publications

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Browsing Physics and Astronomy Publications by Author "Abraham, E.R.I."

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    Hyperfine structure in photoassociative spectra of Li26 and Li2
    (American Physical Society, 1996) Abraham, E.R.I.; McAlexander, W.I.; Stoof, H.T.C.; Hulet, R.G.; Rice Quantum Institute
    We present spectra of hyperfine resolved vibrational levels of the A1Σ+uand 13Σ+g states of Li26 and Li27 obtained via photoassociation of colliding ultracold atoms in a magneto-optical trap. A simple first-order perturbation theory analysis accurately accounts for the frequency splittings and relative transition strengths of all observed hyperfine features. Assignment of the hyperfine structure allows accurate determination of a vibrational level center of gravity, which significantly decreases the experimental uncertainty of vibrational energies. Differences in the spectra of Li26 and Li27 are attributed to quantum statistics. The 13Σ+g series obeys Hund’s case bβS coupling and the hyperfine constant is extracted for both isotopes.
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    Precise atomic radiative lifetime via photoassociative spectroscopy of ultracold lithium
    (American Physical Society, 1995) McAlexander, W.I.; Abraham, E.R.I.; Ritchie, N.W.M.; Williams, C.J.; Stoof, H.T.C.; Hulet, R.G.; Rice Quantum Institute
    We have obtained spectra of the high-lying vibrational levels of the 13Σ+g state of Li26 via photoassociation of ultracold Li6 atoms confined in a magneto-optical trap. The 13Σ+g state of the diatomic molecule correlates to a 2S1/2 state atom plus a 2P1/2 state atom. The long-range part of the molecular interaction potential for this state depends on the 2P atomic radiative lifetime. By calculating the energy eigenvalues of a model potential for the 13Σ+g state and fitting them to the experimentally measured vibrational levels, we have extracted a value for the 2P lifetime of 26.99±0.16 ns. The precision is currently limited by the accuracy of a region of the model potential provided by ab initio calculations.
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    Radiative lifetime of the 2P state of lithium
    (American Physical Society, 1996) McAlexander, W.I.; Abraham, E.R.I.; Hulet, R.G.; Rice Quantum Institute
    We determine the radial dipole moment between the 2S and 2P states of atomic lithium by analyzing the long-range vibrational eigenenergies of the singly excited diatomic molecule. The result can be expressed in terms of the 2P12 radiative lifetime of Li7, which is found to be 27.102(2)(7) ns. This result agrees with most current atomic-structure calculations and resolves the long-standing disagreement with previous experiment. The current level of precision is sensitive to relativistic effects in the atomic-structure calculation and to non-Born-Oppenheimer and radiation retardation effects in the molecule.
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    Singlet s-wave scattering lengths of Li6 and Li
    (American Physical Society, 1996) Abraham, E.R.I.; McAlexander, W.I.; Gerton, J.M.; Hulet, R.G.; Côté, R.; Dalgarno, A.; Rice Quantum Institute
    Photoassociation of ultracold lithium atoms into bound vibrational levels of the AΣu+1 excited state is used to probe the XΣg+1 ground-state interaction potential of Li26 and Li27. It had been predicted that the s-wave photoassociation signal strength would pass through a minimum as a function of vibrational level for positive s-wave scattering length. We report the observation of this novel effect, and use the location of the minimum to precisely determine the singlet s-wave scattering length for both isotopes. The sensitivity of this technique is demonstrated by distinguishing the minima for collisions involving Li7 atoms in different hyperfine states.
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    Spectroscopic Determination of the s-Wave Scattering Length of Lithium
    (American Physical Society, 1995) Abraham, E.R.I.; McAlexander, W.I.; Sackett, C.A.; Hulet, Randall G.; Rice Quantum Institute
    Two-photon photoassociation of colliding ultracold 7Li atoms is used to probe the Σu+3(a) ground state of 7Li2. The binding energy of the least-bound state of this triplet potential, υ=10, is found to be 12.47±0.04 GHz. This spectroscopic information establishes that the s-wave scattering length for 7Li atoms in the F=2, mF=2 state is (−27.3±0.8)a0. The negative sign of the scattering length has important implications as to whether atoms at this doubly spin-polarized state can undergo a Bose-Einstein condensation.
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    Trap-loss collisions of ultracold lithium atoms
    (American Physical Society, 1995) Ritchie, N.W.M.; Abraham, E.R.I.; Xiao, Y.Y.; Bradley, C.C.; Hulet, R.G.; Julienne, P.S.; Rice Quantum Institute
    Accurate measurements are presented of the rate of trap-loss-producing collisions between ultracold magneto-optically trapped Li7 atoms for a range of trap laser intensities and frequencies. Intensities from near the atomic saturation intensity to well above it are investigated. At low intensities, fine-structure-changing collisions cause trap loss with a rate constant of ?10?10 cm3/s. At sufficiently high intensity, the trap can be deep enough to effectively freeze out the dominant fine-structure-changing collisions as a loss mechanism, enabling an accurate comparison of the radiative escape loss rate with theory. At the lowest intensities of this radiative escape regime, the measured loss rates compare favorably with those calculated using an optical Bloch equation theory and a three-dimensional model of trap depth. However, the intensity dependence of the measured rates does not show the saturation predicted by the optical Bloch equation theory. It is shown that reliable knowledge of trap depth is necessary to accurately compare experiment with theory.
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    Triplet s-wave resonance in Li6 collisions and scattering lengths of Li6 and Li7
    (American Physical Society, 1997) Abraham, E.R.I.; McAlexander, W.I.; Gerton, J.M.; Hulet, R.G.; Côté, R.; Dalgarno, A.; Rice Quantum Institute
    The triplet s-wave scattering length of Li6 is determined using two-photon photoassociative spectroscopy of the diatomic a3Σ+u state of Li26. The measured binding energy of the highest-lying bound state, combined with knowledge of the potential, determines the s-wave scattering length to be (-2160±250)a0, where a0 is the Bohr radius. This extraordinarily large scattering length signifies a near-threshold resonance. A complete table of singlet and triplet scattering lengths for collisions involving Li6 and Li7 determined from this and our previous spectroscopic investigations is given.