Single-Photon Atomic Cooling - Raizen Lab - The University of ...

a) b) c) d) e)
external
potential
one-way-wall
Figure 1.5: (a) An atom is placed in an external confining potential along
with a one-way-wall which is initially placed such that the atom does not have
sufficient energy to reach it. (b) The one-way-wall is slowly swept towards
the trap center, so that the atom first encounters it at its turning point. (c)
The one-way-wall continues to sweep in, eventually returning the cold atom to
the center of the external confining potential (d). (e) The one-way-wall moves
away from the region containing the atoms.
the increase in potential energy of the atom [21]. This is completely analogous
to the fact that the work done by an ideal elevator is equal to the change in
the potential energy of its occupants. After sweeping through the center of
the external confining potential the atom remains trapped at its center, but is
now cold [Fig. 1.5(d)]. The one-way-wall continues its sweep out of the region
of the atom [Fig. 1.5(e)].
Because this scheme is fundamentally a single atom process, it works
equally well on an ensemble of non-interacting atoms. To work on an ensemble
the one-way-wall must be initially positioned such that the most energetic atom
in the group does not have sufficient energy to reach it (Fig. 1.6). The rate
at which the one-way-wall is swept must be slow enough to allow all atoms in
the ensemble to reach it with negligible kinetic energy. Because this technique
operates at the single particle level it does not rely on a specific form of inter-
14