Cold Dipolar Gases in Optical Lattices - Frustration and Disorder

When atoms are cooled down to extremely low temperatures they start to show quantum mechanical properties on a macroscopic scale. The phenomenon of Bose-Einstein condensation (BEC) is one of the best known manifestations of this behavior. The recent experimental success in achieving a BEC in optical lattices, where the interactions among the atoms are larger than the energy of their motion, allows for a new possibility to control them. Because of the strong repulsion the atoms prefer to sit on different lattice sites and form a Mott-insulator where every site is occupied precisely by one atom. If these particles interact over long distances as is the case for dipolar chromium atoms, they can rearrange on the lattice to form very interesting checkerboard structures with the number of atoms changing from one site to another modulated by the period of the lattice. In addition they can form a supersolid which is a crystal with superfluid properties. If we create an optical lattice formed from periodically repeating triangles, the interaction between the particles on neighboring sites will give rise to frustration, the phenomenon which is extensively studied in applications to quantum magnets and superconductivity. It arises when there are many possible configurations of the particles on a lattice which have the same energy. Because of the frustration the atoms on the triangular lattice will show many interesting phases with novel properties. To study dipolar atoms on a lattice is not only of fundamental interest, chromium is a basic material in lithography processes and better understanding of its properties will provide a route towards smaller microchips and faster computers. Furthermore dipolar atoms are promising candidates in the development of robust quantum computers.