Fast convergence of white noise cross-correlation measurement archived by vector average in both frequency and time domain

摘要

White noise measurement can provide very useful information in addition tonormal transport measurements. For example thermal noise measurement can beused at sub Kelvin temperature to determine the absolute electron temperaturewithout applying any heating current. And shot noise measurements helped tounderstand the properties of nano and mesoscopic normal metal/superconductorstructures. But at low temperature and for relatively small resistance it isdifficult to measure the sample's noise magnitude because the backgroundthermal noise can be much larger and usually there are other pick-up noises.Cross correlation technique is one way to solve this problem. This articledescribes an improved cross correlation algorithm that averages in bothfrequency and time domain, and the realization of a simple instrument set-upwith PC and sound card. With this set-up it is shown even with much largerbackground noise and pickup noises, 100pV/$\sqrt{Hz}$ white noise level can beeasily measured in seconds. Compared to the normally used cross-correlationmethods, it is several orders of magnitude faster.