Tailored periodic potentials in atom optics

Summary form only given.We used argon atoms in the metastable long-lived 1s/sub 5/ state. This state has a transition (at 801 nm) where the excited state decays predominately (70%) to the ground state. Varying the detuning of a 801-nm standing light wave, we could thus realize any real, complex, or imaginary sinusoidal potential for the metastable argon atoms. Our detector can only register the metastable state, and therefore atoms pumped to the ground state will escape detection. We performed experiments studying the coherent motion of atoms in crystals.