Quantum Physics
Quantum phase transition to unconventional multi-orbital superfluidity in optical lattices
18 April 2011
Photo: AG Sengstock
We observe a novel multi-orbital superfluid phase with a complex order parameter in binary spin mixtures. In this unconventional superfluid, the local phase angle of the complex order parameter is continuously twisted between neighboring lattice sites. The nature of this twisted superfluid quantum phase is an interaction-induced admixture of the p-orbital favored by the graphene-like band structure of the hexagonal optical lattice used in the experiment. We observe a second-order quantum phase transition between the normal superfluid and the twisted superfluid phase which is accompanied by a symmetry breaking in momentum space.