Magnetic Trapping
We say a particle is trapped if the average force on it is directed toward a single point or region called the trap center. The Coulomb force can trap ions or other charged particles, but neutral atoms have no such electric handles. Trapping them requires the use of an electric dipole moment that is induced by light (many neutral molecules have a permanent electric dipole moment but atoms do not), or a permanent magnetic dipole moment. Unlike the Coulomb force, dipole forces derive from the field gradient, not the field strength. Both electric and magnetic dipole traps are widely used, but our work used the permanent magnetic dipole moment that arises from both the electron's orbital motion and its intrinsic dipole moment in an inhomogeneous magnetic field. .
The first neutral atom trap ever was magnetic and used the simplest possible arrangement, namely, a pair of coaxial coils carrying oppositely directed currents (anti-Helmholtz configuration). The field is zero at the geometric center of the coil pair, but nowhere else, and so there is always a field magnitude gradient toward the center that attracts weak-field seekers (Maxwell's equations preclude a local field maximum). As long as the atomic motion in the trap is slow enough that the atomic magnetic moment can follow the changing field orientation as the atom orbits around in the trap, this condition is preserved (see Ref. [2]). But passage through the field zero at the center violates this adiabaticity and the consequent Majorana transitions can cause the atoms to be ejected from the trap (see Ref. [5]). Many variations of magnetic traps have been developed where the field minimum is not zero and therefore avoid this problem.
The trap depth is limited by the maximum field value, and this is typically quite small, so atomic samples have to be cooled to enable trapping. It's possible to cool them enough so that their deBroglie wavelength is comparable to their orbital size, and then their motion requires a quantum mechanical description.