Preparation and spectroscopy of a metastable Mott insulator state with   attractive interactions
  We prepare and study a metastable attractive Mott insulator state formed with bosonic atoms in a three-dimensional optical lattice. Starting from a Mott insulator with Cs atoms at weak repulsive interactions, we use a magnetic Feshbach resonance to tune the interactions to large attractive values and produce a metastable state pinned by attractive interactions with a lifetime on the order of 10 seconds. We probe the (de-)excitation spectrum via lattice modulation spectroscopy, measuring the interaction dependence of two- and three-body bound state energies. As a result of increased on-site three-body loss we observe resonance broadening and suppression of tunneling processes that produce three-body occupation. 
Manfred J. Mark and Elmar Haller and Katharina Lauber and Johann G.   Danzl and Alexander Janisch and Hans Peter B\"uchler a...
cond-mat.quant-gas quant-ph