Experiments with Supersonic Beams as a Source of Cold Atoms
Experiments with Supersonic Beams as a Source of Cold Atoms
Experiments with Supersonic Beams as a Source of Cold Atoms
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show that the acceptance volume in ph<strong>as</strong>e space <strong>of</strong> a magnetic adiabatic decelerator<br />
is well matched to the ph<strong>as</strong>e space volume <strong>of</strong> a supersonic beam after the skimmer.<br />
This means that the adiabatic decelerator should capture the greatest possible flux<br />
at the highest possible ph<strong>as</strong>e space density. The configuration used in these l<strong>as</strong>t<br />
experiments is the one which will be implemented here.<br />
5.4.3 Single-Photon Cooling <strong>of</strong> Hydrogen<br />
The coilgun method can bring samples <strong>of</strong> atoms to rest in the laboratory frame,<br />
where they can then be trapped at temperatures in the tens <strong>of</strong> millikelvin. For some<br />
applications though, the trapped atoms need to be colder than this. For true precision<br />
spectroscopy, trapping the atoms in a magic wavelength optical trap would be ideal<br />
[129], and this requires cooling the atoms to load them into the shallower optical<br />
potential. Studies <strong>of</strong> degenerate g<strong>as</strong>es also require further cooling, since efficient<br />
evaporative cooling to degeneracy requires a high initial ph<strong>as</strong>e space density to enable<br />
collisions and short rethermalization times. This section presents a general cooling<br />
technique called single-photon cooling, which is capable <strong>of</strong> cooling nearly any species<br />
to the recoil limit [130–134]. A proposed scheme for applying single-photon cooling<br />
to atomic hydrogen isotopes [81, 135] is discussed.<br />
The principle <strong>of</strong> single-photon cooling is the creation <strong>of</strong> a one-way wall, which<br />
is permeable to atoms approaching the barrier from one direction but not from the<br />
other. A one-way wall permits a sample to be compressed <strong>with</strong>out doing work on it,<br />
thus incre<strong>as</strong>ing the ph<strong>as</strong>e space density. This is illustrated for atoms trapped in a<br />
1D potential in figure 5.25(a). While the wall incre<strong>as</strong>es the ph<strong>as</strong>e space density, the<br />
temperature <strong>of</strong> the sample is not reduced. Figure 5.25(b) illustrates how starting the<br />
wall at the edge <strong>of</strong> the trap and sweeping it slowly through the potential allows the<br />
wall to both compress the sample and reduce its temperature. In this example, the<br />
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