  A qubit sensor with an electric dipole moment acquires an additional
contribution to its depolarization rate when it is placed in the vicinity of a
polar or dielectric material as a consequence of electrical noise arising from
polarization fluctuations in the material. Here, we characterize this
relaxation rate as a function of experimentally tunable parameters such as
sample-probe distance, probe-frequency, and temperature, and demonstrate that
it offers a window into dielectric properties of insulating materials over a
wide range of frequencies and length scales. We discuss the experimental
feasibility of our proposal and illustrate its ability to probe a variety of
phenomena, ranging from collective polar excitations to phase transitions and
disorder-dominated physics in relaxor ferroelectrics. Our proposal paves the
way for a novel table-top probe of polar and dielectric materials in a
parameter regime complementary to existing tools and techniques.
