What quantity is measured in an excess noise experiment?

TL;DR

This paper clarifies that excess noise in mesoscopic current measurements corresponds to the excess of the non-symmetrized power spectrum, applicable across various experimental configurations.

Contribution

It establishes a general theoretical link between excess noise and the non-symmetrized power spectrum in mesoscopic systems.

Findings

Excess noise equals the excess of the non-symmetrized power spectrum.

The result applies broadly to different experimental setups.

Provides a theoretical foundation for interpreting excess noise measurements.

Abstract

Consider a measurement in which the current coming out of a mesoscopic sample is filtered around a given frequency, amplified, measured and squared. Then this process is repeated many times and the results are averaged. Often, two such measurements are performed on the same system in and out of equilibrium (the nonequilibrium state can be obtained by a variety of methods, e.g., by applying a DC voltage or electromagnetic radiation to the sample). The excess noise is defined as the difference in the noise between these two measurements. We find that this excess noise is given by the excess of the non-symmetrized power-spectrum of the current-noise. This result holds for a rather general class of experimental setups.