Optical response of the supersolid polaron

The ground-state properties of the supersolid polaron consisting of a neutral impurity immersed in a dipolar supersolid have recently been studied. Here, the optical response of an impurity in a dipolar supersolid is calculated and interpreted in terms of the contributions of the different excitation modes of the supersolid. The optical absorption spectrum reveals the two Van Hove singularities that correspond to the flattening of the two Goldstone modes of the supersolid at the Brillouin zone edge. A single peak is found in the superfluid regime corresponding to the roton minimum which diverges at the transition. We propose the response of an ionic impurity as an experimental probe for the supersolid excitations and show how this technique can be extended to neutral impurities with an electric or magnetic dipole moment.