We advocate a simple multipole expansion of the polarisation density matrix. The resulting multipoles appear as successive moments of the Stokes variables and can be obtained from feasible measurements. In terms of these multipoles, we construct a wh
ole hierarchy of measures that accurately assess higher-order polarization fluctuations.
We addressed the inconsistency between the electron mass anisotropy ratios determined by the far-infrared experiments and DC conductivity measurements. By eliminating possible sources of error and increasing the sensitivity and resolution in the far-
infrared reflectivity measurement on the single crystalline and on the polycrystalline La1.84Sr0.16CuO4, we have unambiguously identified that the source of the mass anisotropy problem is in the estimation of the free electron density involved in the charge transport and superconductivity. In this study we found that only 2.8 % of the total doping-induced charge density is itinerant at optimal doping. Our result not only resolves the mass anisotropy puzzle but also points to a novel electronic structure formed by the rest of the electrons that sets the stage for the high temperature superconductivity.
At a quantum critical point (QCP) -- a zero-temperature singularity in which a line of continuous phase transition terminates -- quantum fluctuations diverge in space and time, leading to exotic phenomena that can be observed at non-zero temperatures
. Using a quantum antiferromagnet, we present calorimetric evidence that nuclear spins frozen in a high-temperature metastable state by temperature quenching are annealed by quantum fluctuations near the QCP. This phenomenon, with readily detectable heat release from the nuclear spins as they are annealed, serves as an excellent marker of a quantum critical region around the QCP and provides a probe of the dynamics of the divergent quantum fluctuations.
