Observation of momentum-induced broadening of width in narrow Feshbach resonances of ultracold ¹³³Cs atoms

Interactions between atoms in ultracold quantum gases play an important role in the study of the quantum simulation of many-body physics. Feshbach resonance is a versatile tool to control atomic interactions, where the atom-loss spectra are widely used to characterize Feshbach resonances of various atomic species. Here, we report the experimental observation of momentum-induced broadening of widths in atom-loss spectra of narrow ¹³³Cs Feshbach resonances. We drive Bragg excitation to kick the Bose–Einstein condensate of Cs atoms in a cigar-shaped optical trap, and measure the atom-loss spectra of narrow Feshbach resonances of moving ultracold atoms near the magnetic fields 19.84 G and 47.97 G. We show that the widths of the atom-loss spectra are broadened for the atoms with the momenta of 2ħk and 4ħk, and even observe splitting in the Feshbach resonance of the atoms with momentum 4ħk. Our work may open the way for exploring the interesting physical phenomena arising from the collective velocity of colliding atoms that have been ignored in general.