Production of strongly bound 39K bright solitons

We report on the production of K-39 matter-wave bright solitons, i.e., one-dimensional matter waves that propagate without dispersion thanks to attractive interactions. The volume of the soliton is studied as a function of the scattering length through three-body losses, revealing peak densities as high as similar to 5 x 10(20) m(-3). Our solitons, close to the collapse threshold, are strongly bound and will find applications in fundamental physics and atom interferometry.