  A vortex in a superfluid gas inside an optical lattice can behave as a
massive particle moving in a periodic potential and exhibiting quantum
properties. In this Letter we discuss these properties and show that the
excitation of vortex motions in a two-dimensional lattice can lead to striking
measurable changes in its dynamic response. It would be possible by means of
Bragg spectroscopy to carry out the first direct measurement of the effective
vortex mass, the pinning to the underlying lattice, and the dissipative
damping.
