  We propose an Andreev interferometer, based on a branched Y-junction, to
detect the finite momentum pairing in Fulde-Ferrell (FF) superconductors. In
this interferometer, the oscillation of subgap conductance is a unique function
of phase difference between the two channels of the Y-junction, which is
determined by the phase modulation of the order parameter in the FF
superconductors. This interferometer has the potential not only to determine
the magnitude but also the direction of the momentum of Cooper pairs in the FF
superconductor. The possible applications of the interferometer in the
identification of the finite momentum pairing in non-centrosymmetric
superconductors are also discussed.
