"Atoms in a BEC behave like a single macroscopic matter wave that extends across the ensemble, and the spatial resolution of the ion microscope is high enough to probe phenomena on a scale similar to the length at which the matter wave changes." -- 
"Atoms in a BEC behave like a single macroscopic matter wave that extends across the ensemble, and the spatial resolution of the ion microscope is high enough to probe phenomena on a scale similar to the length at which the matter wave changes." --
It’s big enough for them to see it.