Spin relaxation and band excitation of a dipolar BEC in 2D optical lattices

We observe interband transitions mediated by dipole-dipole interactions for an array of 1D quantum gases of chromium atoms, trapped in a 2D optical lattice.
arXiv:1010.3241 (2010) / Phys. Rev. Lett. 106, 015301 (2011)

Interband transitions occur when dipolar relaxation releases an energy larger than the lattice band gap. For symmetric lattice sites, and a magnetic field parallel to the lattice axis, we compare the measured dipolar relaxation rate with a Fermi golden rule calculation.

Below a magnetic field threshold, we obtain an almost complete suppression of dipolar relaxation, leading to metastable 1D gases in the highest Zeeman state.

Band mapping results above threshold. (a) Integrated population profile along z: the first excited band (second Brillouin zone, BZ) in the y direction is populated, contrary to below threshold. (b) Integrated profile along y showing a non-Gaussian velocity distribution.