In order for atoms to remain trapped in a magnetic trap, their magnetic moments have to point in the opposite direction of the magnetic field. But the magnetic field vanishes at the center of a spherical quadrupole trap. This means that atoms at the center of the trap can become "confused" and lose their allignment when they pass through the center of the trap where there is no field to guide them. When atoms flip their magnetic moment like this, we call it a Majorana flop. These Majorana flops make such a trap leaky, as if there were a hole in the center.
In 1995 we succeeded in using a focused beam from an argon ion laser to repel atoms from the center of the trap, effectively plugging the hole in the trap. Using this method we were able to cool our atoms below the critical temperature for Bose-Einstein condensation.