We localize Cs atoms in wavelength-sized potential wells of an optical lattice, and cool them to a three-dimensional temperature of 700 nK by adiabatic expansion. In the optical lattice we precool the atoms to $\approx 1\mu \mathrm{K}$. We then reduce the trapping potential in a few hundred $\mu$s, causing the atomic center-of-mass distribution to expand and the temperature to decrease by an amount which agrees with a simple 3D band theory. These are the lowest 3D kinetic temperatures ever measured.

• Received 8 June 1994

DOI:https://doi.org/10.1103/PhysRevLett.74.1542