Bosonic Double Lattice Ring Under Artificial Gauge Fields

We consider a system of weakly interacting bosons confined on a planar double lattice ring subjected to two artificial gauge fields. We determine its ground state by solving coupled discrete non-linear Schr\"odinger equations at mean field level. At varying inter-ring tunnel coupling, flux and interactions we identify the vortex, Meissner and biased-ladder phases also predicted for a bosonic linear ladder by a variational Ansatz, as well as other phases, such as a density wave and an imbalanced vortex phase. We also find peculiar features associated to the ring geometry, in particular parity effects in the number of vortices, and the appearance of a single vortex in the Meissner phase. We show that the persistent currents on the rings carry precise information on the various phases. Finally, we propose a way of observing the Meissner and vortex phases via spiral interferogram techniques.