Browsing by Author "Stoof, H.T.C."
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Item Bright Soliton Trains of Trapped Bose-Einstein Condensates(American Physical Society, 2002) Khawaja, U. Al; Stoof, H.T.C.; Hulet, R.G.; Strecker, K.E.; Partridge, G.B.; Rice Quantum InstituteWe variationally determine the dynamics of bright soliton trains composed of harmonically trapped Bose-Einstein condensates with attractive interatomic interactions. In particular, we obtain the interaction potential between two solitons. We also discuss the formation of soliton trains due to the quantum mechanical phase fluctuations of a one-dimensional condensate.Item Deformation of a Trapped Fermi Gas with Unequal Spin Populations(American Physical Society, 2006) Partridge, G.B.; Li, Wenhui; Liao, Y.A.; Hulet, R.G.; Haque, M.; Stoof, H.T.C.; Rice Quantum InstituteThe real-space densities of a polarized strongly interacting two-component Fermi gas of Li6 atoms reveal two low-temperature regimes, both with a fully paired core. At the lowest temperatures, the unpolarized core deforms with increasing polarization. Sharp boundaries between the core and the excess unpaired atoms are consistent with a phase separation driven by a first-order phase transition. In contrast, at higher temperatures the core does not deform but remains unpolarized up to a critical polarization. The boundaries are not sharp in this case, indicating a partially polarized shell between the core and the unpaired atoms. The temperature dependence is consistent with a tricritical point in the phase diagram.Item Elastic and inelastic collisions of 6Li atoms in magnetic and optical traps(American Physical Society, 1998) Houbiers, M.; Stoof, H.T.C.; McAlexander, W.I.; Hulet, R.G.; Rice Quantum InstituteWe use a full coupled-channels method to calculate collisional properties of magnetically or optically trapped ultracold 6Li. The magnetic-field dependence of the s-wave scattering lengths of several mixtures of hyperfine states are determined, as are the decay rates due to exchange collisions. In one case, we find Feshbach resonances at B=0.08T and B=1.98T. We show that the exact coupled-channels calculation is well approximated over the entire range of magnetic fields by a simple analytical calculation.Item Growth and Collapse of a Bose-Einstein Condensate with Attractive Interactions(American Physical Society, 1998) Sackett, C.A.; Stoof, H.T.C.; Hulet, R.G.; Rice Quantum InstituteWe consider the dynamics of a quantum degenerate trapped gas of 7Li atoms. Because the atoms have a negative s-wave scattering length, a Bose condensate of 7Li becomes mechanically unstable when the number of condensate atoms approaches a maximum value. We calculate the dynamics of the collapse that occurs when the unstable point is reached. In addition, we use the quantum Boltzmann equation to investigate the nonequilibrium kinetics of the atomic distribution during and after evaporative cooling. The condensate is found to undergo many cycles of growth and collapse before a stationary state is reached.Item 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 InstituteWe 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.Item 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 InstituteWe 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.Item Superfluid state of atomic 6Li in a magnetic trap(American Physical Society, 1997) Houbiers, M.; Ferwerda, R.; Stoof, H.T.C.; McAlexander, W.I.; Sackett, C.A.; Hulet, R.G.; Rice Quantum InstituteWe report on a study of the superfluid state of spin-polarized atomic 6Li confined in a magnetic trap. Density profiles of this degenerate Fermi gas and the spatial distribution of the BCS order parameter are calculated in the local-density approximation. The critical temperature is determined as a function of the number of particles in the trap. Furthermore, we consider the mechanical stability of an interacting two-component Fermi gas, in the case of both attractive and repulsive interatomic interactions. For spin-polarized 6Li we also calculate the decay rate of the gas and show that within the mechanically stable regime of phase space, the lifetime is long enough to perform experiments on the gas below and above the critical temperature if a bias magnetic field of about 5 T is applied. Moreover, we propose that a measurement of the decay rate of the system might signal the presence of the superfluid state.Item Superfluidity of Spin-Polarized 6Li(American Physical Society, 1996) Stoof, H.T.C.; Houbiers, M.; Sackett, C. A.; Hulet, R.G.; Rice Quantum InstituteWe study the prospects for observing superfluidity in a spin-polarized atomic gas of 6Li atoms, using state-of-the-art interatomic potentials. We determine the spinodal line and show that a BCS transition to the superfluid state can indeed occur in the (meta)stable region of the phase diagram if the densities are sufficiently low. We also discuss the stability of the gas due to exchange and dipolar relaxation and conclude that the prospects for observing superfluidity in a magnetically trapped atomic 6Li gas are particularly promising for magnetic bias fields larger than 10 T.