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arXiv:1009.0926 · Comptes Rendus Physique

Study of Efimov physics in two nuclear-spin sublevels of 7Li

Noam Gross, Zav Shotan, Olga Machtey, S. J. J. M. F. Kokkelmans, Lev Khaykovich

Published Jan 1, 2011• 67 citations
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Abstract

Efimov physics in two nuclear-spin sublevels of bosonic lithium is studied and it is shown that the positions and widths of recombination minima and Efimov resonances are identical for both states within the experimental errors, which indicate that the short-range physics is nuclear-spin independent. We also find that the Efimov features are universally related across Feshbach resonances. These results crucially depend on careful mapping between the scattering length and the applied magnetic field which we achieve by characterization of the two broad Feshbach resonances in the different states by means of rf-spectroscopy of weakly bound molecules. By fitting the binding energies numerically with a coupled channels calculation we precisely determine the absolute positions of the Feshbach resonances and the values of the singlet and triplet scattering lengths.

DOI
10.1016/j.crhy.2010.10.004

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Efimov physics in two nuclear-spin sublevels of bosonic lithium is studied and it is shown that the positions and widths of recombination minima and Efimov resonances are identical for both states within the experimental errors, which indicate that the short-range physics is nuclear-spin independent. We also find that the Efimov features are universally related across Feshbach resonances. These results crucially depend on careful mapping between the scattering length and the applied magnetic field which we achieve by characterization of the two broad Feshbach resonances in the different states by means of rf-spectroscopy of weakly bound molecules. By fitting the binding energies numerically with a coupled channels calculation we precisely determine the absolute positions of the Feshbach resonances and the values of the singlet and triplet scattering lengths.
We investigate three-body recombination loss across a Feshbach resonance in a gas of ultracold 7Li atoms prepared in the absolute ground state and perform a comparison with previously reported results of a different nuclear-spin state [N. Gross, Phys. Rev. Lett. 103, 163202 (2009)]. We extend the previously reported universality in three-body recombination loss across a Feshbach resonance to the absolute ground state. We show that the positions and widths of recombination minima and Efimov resonances are identical for both states which indicates that the short-range physics is nuclear-spin independent.
Universality is a fundamental property of diverse few-body systems such as atomic nuclei, simple molecules or ultracold atoms. It is related to a peculiar quantum mechanical phenomenon which was discovered by Russian theoretician Vitaly Efimov in the early 1970-s. A consequence of his prediction was the existence of an infinite number of bound energy levels for three particles even if a short-range two-body potential is just not deep enough to bind two particles together. This counterintuitive discovery attracted a great deal of interest but lacked an experimental verification for many years. Difficulties in finding a system where the inter-particle potential can be changed easily were answered recently with the experimental demonstration of Feshbach resonances in ultracold atoms. In the limit of zero collision energy the two-body interactions are determined by a single parameter, the scattering length a, which is defined by the low energy s-wave scattering phase-shift. In the vicinity of a Feshbach resonance this parameter diverges and thus can be readily tuned to large values and different signs by an experimentally easy-to-use change of the external magnetic field. A universal behavior is expected when a becomes the largest length scale in the system. In this case the three-body observables depend only on the scattering length and on a three-body parameter which serves as a boundary condition for the short range physics. The first experimental evidence for the existence of Efimov quantum states was reported in 2006 in a system of ultracold Cs atoms by the Innsbruck group. They investigated three-body recombination induced loss of atoms from a shallow optical trap and showed the enhancement of this loss at certain values of the scattering length. It was
We have measured the binding energy of 7{}^{7}7Li Feshbach molecules deep into the nonuniversal regime by associating atoms in a Bose-Einstein condensate with a modulated magnetic field. We extract the scattering length from these measurements, correcting for nonuniversal short-range effects using the field-dependent effective range. With this more precise determination of the Feshbach resonance parameters we reanalyze our previous data on the location of atom loss features produced by the Efimov effect [Pollack et al., Science 326, 1683 (2009)]. We find the measured locations of the three- and four-body Efimov features to be consistent with universal theory at the 20%--30% level.
We report on experimental evidence of universality in ultracold 7Li atoms' three-body recombination loss in the vicinity of a Feshbach resonance. We observe a recombination minimum and an Efimov resonance in regions of positive and negative scattering lengths, respectively, which are connected through the pole of the Feshbach resonance. Both observed features lie deeply within the range of validity of the universal theory, and we find that the relations between their properties, i.e., widths and locations, are in excellent agreement with the theoretical predictions.
We study the interspecies scattering properties of ultracold Li–Cs mixtures in their two energetically lowest spin channels in the magnetic field range between 800 and 1000 G. Close to two broad Feshbach resonances (FR) we create weakly bound LiCs dimers by radio-frequency association and measure the dependence of their binding energy on the external magnetic field strength. Based on the binding energies and complementary atom loss spectroscopy of three other Li–Cs s -wave FRs we construct precise molecular singlet and triplet electronic ground state potentials using a coupled-channels calculation. We extract the Li–Cs interspecies scattering length as a function of the external field and obtain almost a ten-fold improvement in the precision of the values for the pole positions and widths of the s -wave FRs as compared to our previous work (Pires et al 2014 Phys. Rev. Lett. 112 250404 ). We discuss implications on the Efimov scenario and the universal geometric scaling for LiCsCs trimers.
Abstract Efimov physics in the vicinity of two overlapping narrow Feshbach resonances can be explored within a framework of a three-channel model where a non-interacting open channel is coupled to two closed molecular channels. Here, we determine how it compares to the extended two-channel model, which includes an open channel with finite background scattering and a single molecular channel. We identify the parameter range in which the three-channel model surpasses the extended two-channel model. Furthermore, the three-channel model is extended to include background scattering, and then both models are applied to the experimentally relevant system of bosonic lithium atoms polarized on two different energy levels, with an isolated and two overlapping narrow Feshbach resonances, respectively. We confirm, in agreement with previous studies, that being small, the background scattering length in lithium has a negligible effect on the Efimov features in the case of isolated resonance. However, in the case of overlapping Feshbach resonances, the inclusion of background scattering improves the performance of the theory with respect to the experimentally measured position of the Efimov resonance.