All-optical production of 7Li Bose-Einstein condensation using Feshbach resonances

We show an all-optical method of making 7Li condensate using tunability of the scattering length in the proximity of a Feshbach resonance. We report the observation of two new Feshbach resonances on |F = 1;mF = 0> state. The narrow (broad) resonance of 7 G (34 G) width is detected at 831 +- 4 G (884 +4 -13 G). Position of the scattering length zero crossing between the resonances is found at 836 +- 4 G. The broad resonance is shown to be favorable for run away evaporation which we perform in a crossed-beam optical dipole trap. Starting directly form the phase space density of a magneto-optical trap we observe a Bose-Einstein condensation threshold in less than 3 s of forced evaporation.Comment: 5 pages, 5 figure

Deviation from one-dimensionality in stationary properties and collisional dynamics of matter-wave solitons

By means of analytical and numerical methods, we study how the residual three-dimensionality affects dynamics of solitons in an attractive Bose-Einstein condensate loaded into a cigar-shaped trap. Based on an effective 1D Gross-Pitaevskii equation that includes an additional quintic self-focusing term, generated by the tight transverse confinement, we find a family of exact one-soliton solutions and demonstrate stability of the entire family, despite the possibility of collapse in the 1D equation with the quintic self-focusing nonlinearity. Simulating collisions between two solitons in the same setting, we find a critical velocity, $V_{c}$, below which merger of identical in-phase solitons is observed. Dependence of $V_{c}$ on the strength of the transverse confinement and number of atoms in the solitons is predicted by means of the perturbation theory and investigated in direct simulations. Symmetry breaking in collisions of identical solitons with a nonzero phase difference is also shown in simulations and qualitatively explained by means of an analytical approximation.Comment: 10 pages, 7 figure

Universal Dimer in a Collisionally Opaque Medium: Experimental Observables and Efimov Resonances

A universal dimer is subject to secondary collisions with atoms when formed in a cloud of ultracold atoms via three-body recombination. We show that in a collisionally opaque medium, the value of the scattering length that results in the maximum number of secondary collisions may not correspond to the Efimov resonance at the atom-dimer threshold and thus can not be automatically associated with it. This result explains a number of controversies in recent experimental results on universal three-body states and supports the emerging evidence for the significant finite range corrections to the first excited Efimov energy level.Comment: 5 pages, 2 figure

Three-body recombination at vanishing scattering lengths in an ultracold Bose gas

We report on measurements of three-body recombination rates in an ultracold gas of $^7$Li atoms in the extremely nonuniversal regime where the two-body scattering length vanishes. We show that the rate is well defined and can be described by two-body parameters only: the scattering length $a$ and the effective range $R_e$. We find the rate to be energy independent, and, by connecting our results with previously reported measurements in the universal limit, we cover the behavior of the three-body recombination in the whole range from weak to strong two-body interactions. We identify a nontrivial magnetic field value in the nonuniversal regime where the rate should be strongly reduced.Comment: Version with enhanced supplemental material

Nuclear-spin-independent short-range three-body physics in ultracold atoms

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 et.al., 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.Comment: 4 pages, 2 figure