Experiments to Control Atom Number and Phase-Space Density in ...

neglect the effect of the spontaneously scattered photon. The final volume Vf occupied
by the gas is now dependent only on the residual internal energy. By reducing the
internal energyUf, the final volumeVf will therefore also be minimized. The efficiency of
the cooling method will therefore benefit immensely from the removal of kinetic energy
from the system. Typically the spontaneously scattered photon can be neglected for
the experiments presented in this dissertation, however, the single-photon recoil is the
fundamental limit to phase-space densities achievable by single-photon cooling.
3.4 Maxwell’s Demon
In 1867 James Clerk Maxwell proposed a gedankenexperiment commonly referred
to as Maxwell’s demon [62]. In the original idea a ”very observant and neat-fingered
being” could sort a gas of atoms or molecules according to their velocities into two
separate halves of one container by operating a massless trap door. He argued that
if the demon could sense the velocity of the atoms as they approached and sort them
accordingly, a temperature differential between the two vessels could be created without
doing any work, seemingly violating the second law of thermodynamics. An illustration
of Maxwell’s original demon is shown in figure 3.4.
A B A B
Figure 3.4: Maxwell’s demon allows hot atoms (red) to move from A to B, and cold
atoms (blue) to move from B to A. No work is done on the massless gate, but a
temperature differential is created. Figure adapted from Travis Bannerman.
Later on Maxwell modified the original concept to a demon as illustrated in
figure 3.5. In this scenario a ”less intelligent” demon watches the atoms and allows
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