The researchers loaded ultracold rubidium atoms into one-dimensional tubes formed by a two-dimensional lattice (the third standing wave is initially off). This lattice is strong so that the atoms have insufficient energy to tunnel between neighboring tubes. The interaction is too low for the transition to the TG regime. For that, the third axis of the lattice is used. It is set to a lower intensity and shorter time than the other two, so that tunneling in this direction is possible. For increasing intensity of the third lattice, atoms in the same lattice well are more and more tightly trapped, which increases the collisional energy. When the collisional energy becomes much bigger than the tunneling energy, the atoms can still tunnel into empty lattice wells, but not into or across occupied ones.