Van der Waals-Zeeman Colloquium

Thursday, 13 Nov 2007, 16:00h

When ultracold atoms pair up in an optical lattice

Johannes Hecker Denschlag
Institut für Experimentalphysik, Universität Innsbruck, 6020 Innsbruck

Ultracold atoms in a 3-dimensional optical lattice represent an intriguing playground to study fundamental physics and chemistry. After preparing an atomic quantum lattice gas with exactly two atoms per lattice site, we explore various chemical and non-chemical binding regimes of the atomic pairs. First we create the most weakly bound Rb2 molecules in the electronic ground state by ramping over a Feshbach resonance. These molecules are in a precisely defined quantum state and exhibit a long lifetime. Using optical STIRAP (stimulated Raman adiabatic passage) or a novel radio frequency sweep method (ATAC), we can efficiently transfer these Feshbach molecules to a more deeply bound vibrational level. In this way we can create well defined mixtures and coherent superpositions of molecular states which can later be used to investigate molecular properties and collisions. Besides studying chemically bound molecules, optical lattices also allow forming a novel kind of stable bound state of two atoms which is based on repulsion rather than attraction between the particles. We will explain how these lattice-induced repulsively bound atom pairs come about and discuss their interesting properties.