Coherent dimer formation near Feshbach resonances in Bose-Einstein condensates (original) (raw)
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Physical Review A, 2007
We predict the resonance enhanced magnetic field dependence of atom-dimer relaxation and three-body recombination rates in a 87 Rb Bose-Einstein condensate (BEC) close to 1007 G. Our exact treatments of threeparticle scattering explicitly include the dependence of the interactions on the atomic Zeeman levels. The Feshbach resonance distorts the entire diatomic energy spectrum causing interferences in both loss phenomena. Our two independent experiments confirm the predicted recombination loss over a range of rate constants that spans four orders of magnitude.
Atom loss from Bose-Einstein condensates due to Feshbach resonance
Physical Review A, 1999
In recent experiments on Na Bose-Einstein condensates [S. Inouye et al, Nature 392, 151 (1998); J. Stenger et al, Phys. Rev. Lett. 82, 2422], large loss rates were observed when a time-varying magnetic field was used to tune a molecular Feshbach resonance state near the state of pairs of atoms belonging to the condensate many-body wavefunction. A mechanism is offered here to account for the observed losses, based on the deactivation of the resonant molecular state by interaction with a third condensate atom, with a deactivation rate coefficient of magnitude ∼ 10 −10 cm 3 /s. 03.75.Fi, 32.80.Pj, 32.60.+i, 34.50.Ez, 34.90.+q Experiments have been carried out recently [1,2] (see also the review [3]) in order to control the interatomic interaction underlying the properties of a Bose-Einstein condensate (BEC). One way to achieve this [1,2] is by tuning a magnetic field B to modify the two-atom scattering length as predicted for a B-dependent Feshbach resonance . The experiments carried out on a Na optical trap measured two distinct features: (a) the change in scattering length and large collisional atom losses with a slow sweep of B that stopped short of the resonant field B 0 , and (b) a near-catastrophic loss of atom density with a fast sweep of B through the B 0 region. Two groups of investigators have recently proposed a unimolecular mechanism to explain the latter feature as due to a fast sweep-induced transfer of population from the ground trap state of an atom pair to excited states.
Dynamics of a molecular Bose-Einstein condensate near a Feshbach resonance
2005
We consider the dissociation of a molecular Bose-Einstein condensate during a magnetic-field sweep through a Feshbach resonance that starts on the molecular side of the resonance and ends on the atomic side. In particular, we determine the energy distribution of the atoms produced after the sweep. We find that the shape of the energy distribution strongly depends on the rate of the magnetic-field sweep, in a manner that is in good agreement with recent experiments.
Three-Body Recombination at Large Scattering Lengths in an Ultracold Atomic Gas
Physical Review Letters, 2003
We study three-body recombination in an optically trapped ultracold gas of cesium atoms with precise magnetic control of the s-wave scattering length a. At large positive values of a, we measure the dependence of the rate coefficient on a and confirm the theoretically predicted scaling proportional to a 4 . Evidence of recombination heating indicates the formation of very weakly bound molecules in the last bound energy level.
Three-body Recombination in Bose Gases with Large Scattering Length
Physical Review Letters, 2000
An effective field theory for the three-body system with large scattering length is applied to three-body recombination to a weakly-bound s-wave state in a Bose gas. Our model independent analysis demonstrates that the three-body recombination constant α is not universal, but can take any value between zero and 67.9ha 4 /m, where a is the scattering length. Other low-energy threebody observables can be predicted in terms of a and α. Near a Feshbach resonance, α should oscillate between those limits as the magnetic field B approaches the point where a → ∞. In any interval of B over which a increases by a factor of 22.7, α should have a zero.
Hartree-Fock-Bogoliubov model and simulation of attractive and repulsive Bose-Einstein condensates
Physical Review A, 2012
We describe a model of dynamic Bose-Einstein condensates near a Feshbach resonance that is computationally feasible under assumptions of spherical or cylindrical symmetry. Simulations in spherical symmetry approximate the experimentally measured time to collapse of an unstably attractive condensate, suggesting that the quantum fluctuations and atom-molecule pairing included in the model are the dominant mechanisms during collapse. Simulations of condensates with repulsive interactions find some quantitative disagreement, suggesting that pairing and quantum fluctuations are not the only significant factors for condensate loss or burst formation. Inclusion of three-body recombination was found to be inconsequential in all of our simulations.
Atom loss and the formation of a molecular Bose-Einstein condensate by Feshbach resonance
Physical Review A, 2000
In experiments conducted recently at MIT on Na Bose-Einstein condensates [S. Inouye et al, Nature 392, 151 (1998); J. Stenger et al, Phys. Rev. Lett. 82, 2422], large loss rates were observed when a time-varying magnetic field was used to tune a molecular Feshbach resonance state near the state of a pair of atoms in the condensate. A collisional deactivation mechanism affecting a temporarily formed molecular condensate [see V. A. Yurovsky, A. Ben-Reuven, P. S. Julienne and C. J. Williams, Phys. Rev. A 60, R765 (1999)], studied here in more detail, accounts for the results of the slow-sweep experiments. A best fit to the MIT data yields a rate coefficient for deactivating atom-molecule collisions of 1.6 × 10 −10 cm 3 /s. In the case of the fast sweep experiment, a study is carried out of the combined effect of two competing mechanisms, the three-atom (atom-molecule) or fouratom (molecule-molecule) collisional deactivation vs. a process of two-atom trap-state excitation by curve crossing [F. H. Mies, P. S. Julienne, and E. Tiesinga, Phys. Rev. A 61, 022721 ]. It is shown that both mechanisms contribute to the loss comparably and nonadditively. 03.75.Fi, 32.80.Pj, 32.60.+i, 34.50.Ez
Collective Oscillations of Two Colliding Bose-Einstein Condensates
Physical Review Letters, 2000
Two 87 Rb condensates (F = 2, m f =2 and m f =1) are produced in highly displaced harmonic traps and the collective dynamical behaviour is investigated. The mutual interaction between the two condensates is evidenced in the center-ofmass oscillations as a frequency shift of 6.4(3)%. Calculations based on a mean-field theory well describe the observed effects of periodical collisions both on the center-of-mass motion and on the shape oscillations. 03.75.Fi, 05.30.Jp, 32.80.Pj, 34.20.Cf Since the first realization of Bose-Einstein condensation with dilute trapped gases [1], systems of condensates in different internal states have deserved attention as mixtures of quantum fluids. In this context, the important issue of the interaction between two distinct condensates was early addressed at JILA [2] with the production of two 87 Rb condensates in the hyperfine levels |F = 2, m f = 2 and |1, −1 in a Ioffe-type trap. Subsequent experiments of the JILA group have focused on the dynamics of two condensates in the states |2, 1 and |1, −1 having nearly the same magnetic moment, confined by a time-orbiting potential (TOP) trap. In these experiments the authors have investigated the effects of the mutual interaction in a situation of almost complete spatial overlap of the two condensates. The resulting dynamics reveals a complex structure, and it is characterized by a strong damping of the relative motion of the two condensates . More recently another group [6] has experimentally investigated a mixture of 87 Rb condensates in different m f states in a TOP trap, but no effects of the mutual interaction have been observed.
Condensation of Pairs of Fermionic Atoms near a Feshbach Resonance
Physical Review Letters, 2004
We have observed Bose-Einstein condensation of pairs of fermionic atoms in an ultracold 6 Li gas at magnetic fields above a Feshbach resonance, where no stable 6 Li2 molecules would exist in vacuum. We accurately determined the position of the resonance to be 822±3 G. Molecular Bose-Einstein condensates were detected after a fast magnetic field ramp, which transferred pairs of atoms at close distances into bound molecules. Condensate fractions as high as 80% were obtained. The large condensate fractions are interpreted in terms of pre-existing molecules which are quasi-stable even above the two-body Feshbach resonance due to the presence of the degenerate Fermi gas.