Experiments with Supersonic Beams as a Source of Cold Atoms

described in section 3.3.1. While two of the coils failed in the course of the experiment,
the remaining 18 coils are able to slow a supersonic beam of metastable neon from
461 m/s to 403 m/s. Importantly, the slowed beam is separated in time from the
initial distribution, allowing it to be easily and clearly observed.
4.4.1 Beam Creation
As noted above, the species slowed in this experiment is metastable neon. In
its ground state electronic configuration, 1s 2 2s 2 2p 6 , neon has a closed shell structure
and J = 0, making it insensitive to magnetic fields (except on the order of the nuclear
magnetic moment which is ≈ 2000 times smaller than electronic magnetic moments).
However, neon can be excited to the 1s 2 2s 2 2p 5 3s 1 configuration. The 3 P2 metastable
state has a lifetime of 14.7 s [83], which is much longer than the few millisecond
duration of these experiments.
In the 3 P2 state, both mJ =1, 2 are low-field-seeking states, and since the
Zeeman shift is directly proportional to mJ, itisthemJ = 2 sublevel which is targeted
and slowed. The 3 P2 state has 5 magnetic sublevels, and atoms in the supersonic beam
should be evenly distributed among these sublevels, at most 20% of metastable atoms
in the beam are in the targeted state. There is also a 3 P0 metastable state in neon,
which probably also makes up some percentage of the initial metastable beam. In
the 3 P2 state, the Landé g-factor is 1.50 [84], which means that the magnetic moment
of the atom is 3μB. The fine structure splitting of the states is around .05 eV and
the magnetic field required to produce a shift of the same energy is around 300 T.
Hence, the fields produced in these experiments are far lower than this, the Zeeman
shift is the appropriate regime for any calculations. To give a sense of scale, the
Zeeman shift at 1 T is .174 meV, and the kinetic energy of a metastable neon atom
at 500 m/s is around 26 meV. Thus, fields of order several Tesla per stage are needed
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