Berry phase caused by nondissipative drag of superflow in a Bose qubit
  A microscopic theory of superfluid drag in a two-component Bose gas is developed. The drag factor is shown to be proportional to the square root of the gas parameter. Basing on the similarity between the drag force and vector potential of magnetic field we propose how the superfluid drag can be used to detect a Berry phase in a Bose counterpart of the Josephson charge qubit. We consider a system in which the drag component, situated inside the drive component, is confined in two half-ring traps separated by two Josephson barriers. Under cyclic adiabatic change of Josephson coupling parameters and an asymmetry of two traps a Berry phase is generated. This phase can be observed though measurements of relative number of atoms in two traps. The Berry phase depends on the drag factor and its detection can be used for determining the value of the drag. 
D. V. Fil, S. I. Shevchenko