Experimental realization of an optical one-way barrier for neutral atoms.

We demonstrate an asymmetric optical potential barrier for ultracold 87Rb atoms using laser light tuned near the D2 optical transition. Such a one-way barrier, where atoms incident on one side are transmitted but reflected from the other, is a realization of Maxwell's demon and has important implications for cooling atoms and molecules not amenable to standard laser-cooling techniques. In our experiment, atoms are confined to a far-detuned dipole trap consisting of a single focused Gaussian beam, which is divided near the focus by the barrier.