The experiment took place in a very high magnetic field generated by a solenoid, a cylindrical winding of coil, in this case made of superconducting magnetic wire. The magnetic field inside the solenoid was high enough to levitate the helium drops, and graded radially to trap the drops at the center. This is the magnetic analog to the gravitational situation of a marble in a mixing bowl. When two drops were placed in the apparatus together, the magnetic fields nudged them both to the center, effectively forcing them into contact. This force was countered by the evaporating gas pressure.
Liquid helium possesses unique properties that make it widely studied in condensed-matter physics.
At a couple of degrees above absolute zero, the liquid changes from a normal fluid into what is known as a superfluid. Superfluids have no viscosity, which enables them to pass through any size hole, and to flow up over the sides of containers. They are also perfect conductors of heat. It is the superfluid properties of liquid helium that support the researchers' theory. Because a superfluid is a perfect heat conductor, the temperature in a superfluid drop is uniform.