Dysprosium dipolar Bose-Einstein condensate with broad Feshbach resonances

We produce Bose-Einstein condensates of ${}^{162}\mathrm{Dy}$ atoms employing an innovative technique based on a resonator-enhanced optical trap that allows efficient loading from the magneto-optical trap. We characterize the scattering properties of the ultracold atoms for magnetic fields between 6 and 30 G. In addition to the typical chaotic distribution of narrow Feshbach resonances in lanthanides, we discover two rather isolated broad features at around 22 G and 27 G. A characterization using the complementary measurements of losses, thermalization, anisotropic expansion, and molecular binding energy points towards resonances of predominant $s$-wave character. Such resonances will ease the investigation of quantum phenomena relying on the interplay between dipole and contact interactions.

Figure 1

(Top) Schematic of the trapping potentials in the vacuum chamber: the resonator trap is shown in red and the optical traps ODT1 and ODT2 in green and in blue, respectively. The angle between ODT1 and the resonator is 8°; the angle between ODT1 and ODT2 is 40°. (Bottom) Power of employed laser beams and phase-space density (PSD) through the experimental cycle. The scheme is divided in stages: (I) MOT compression and resonator trap loading, (II) evaporation in the resonator, (III) transfer from the resonator to the crossed ODT1 and ODT2, and (IV) forced evaporation in the ODTs to Bose-Einstein condensation.

Figure 2

(a) High-resolution atom loss spectroscopy. Line is a guide to the eye. (b) Normalized temperature in the zero-crossing regions after a thermalization experiment. (c) Aspect ratio (AR) of the thermal atomic cloud after 12 ms free expansion from a trap with vertical frequency of 169 Hz and horizontal frequencies of 38 Hz and 107 Hz. (d) Scattering lengths extracted from the data in (c). The dashed and continuous lines are fits of the AR data alone and of the combined AR and binding-energy data, respectively. Open dots are data excluded from the fits. See text for details.

Figure 3

Molecular binding energy for the two broad Feshbach resonances, measured by magnetic-field modulation spectroscopy. (a) Full data range. (b) Zoom of the data close to the resonance centers. The continuous red lines are combined fits of the data close to the centers (open dots) and of the AR data with the models of Eqs. (1) and (2); see text. The dashed blue lines are linear fits to estimate the magnetic moment of the molecular state. Inset: typical molecular association spectrum. The solid line is a fit with the line shape described in [30].