Single-Photon Atomic Cooling

We report the cooling of an atomic ensemble with light, where each atom scatters only a single photon on average. This is a general method that does not require a cycling transition and can be applied to atoms or molecules that are magnetically trapped. We discuss the application of this new approach to the cooling of hydrogenic atoms for the purpose of precision spectroscopy and fundamental tests.

Figure 1

(a) Cross section of the optical box positioned above the cloud of magnetically trapped atoms. In this illustration, two pairs of Gaussian laser sheets propagate parallel to the $x$ axis. A third pair (not visible) propagates parallel to the $y$ axis and completes the optical box. (b) Absorption image along the $z$ axis of approximately $1.5\times {10}^5$ atoms trapped in the optical box.

Figure 2

Incremental atom capture at a fixed translation velocity. The center of the magnetic trap is initially displaced $800\mu \mathrm{m}$ below the optical box and is translated vertically at a velocity of $750\mu \mathrm{m}/\mathrm{s}$. The end point of the translation is varied, and the atom capture, normalized to the maximum number, is plotted as a function of the final separation between the traps. Error bars indicate statistical uncertainties.

Figure 3

Captured atom number as a function of loading time. Data are given for separations between the optical and magnetic trap centers of $800\mu \mathrm{m}$ (▴), $600\mu \mathrm{m}$ (●), $400\mu \mathrm{m}$ (▪), and $200\mu \mathrm{m}$ (▾). Error bars indicate statistical uncertainty, and dashed curves are drawn through the data points to guide the eye. The slopes are initially dominated by the loading rate into the optical box. After some time, the loading rate decreases due to the depletion of the magnetic trap, and the slopes become dominated by escape out of the box.