Progress towards observing quantum fluctuations in matter-wave soliton breathers

Solitons are 1D nonlinear waves that propagate without dispersion. Higher-order solitons, i.e. coherent superpositions of fundamental solitons with specific amplitude ratios, are known as breathers, and can be formed from fundamental solitons using a prescribed interaction quench. Breathers are exactly integrable solutions of the mean-field (MF) nonlinear Schrodinger equation and are immune to dissociation. In quantum many-body theory, however, the relative separation of solitons is no longer conserved, thus endowing the breather with exquisite sensitivity to beyond-MF effects^1,2. We experimentally produce and characterize breathers starting with a bright matter-wave soliton, prepared from a Bose-Einstein condensate (BEC) of ⁷Li confined to a quasi-1D harmonic potential formed from a single focused IR laser beam. The interactions are initially tuned to be slightly attractive using a Feshbach resonance. An nth order breather is created by quenching the strength of the attractive interactions by a factor of n², where n is an integer. We realize both the 2nd and 3rd order breathers, and show how their breathing frequency depends on the number of atoms and the aspect ratio of the quasi-1D trap potential. Our observations agree well with a quasi-1D MF theory. We report the progress made towards observing breather dissociation.

¹V. A. Yurovsky et al., PRL 119, 220401 (2017)

²O.V. Marchukov et. al, Phys. Rev. Lett. 125, 050405 (2020)