An Ultra-Wideband Cross-Correlation Radiometer for Mesoscopic Experiments

We have designed, built and tested a cross-correlation radiometer for detecting statistical order in the quantum fluctuations of mesoscopic experiments at sub-Kelvin temperatures.~ Our system utilizes a fully analog front-end--operating over the X- and Ku-bands (8 to 18 GHz)--for computing the cross-correlation function.~ Digital signal processing techniques are used to provide robustness against instrumentation drifts and offsets.~ The economized version of our instrument can measure, with sufficient correlation efficiency, noise signals having power levels as low as 10 fW.~ We show that, if desired, we can improve this performance by including cryogenic preamplifiers which boost the signal-to-noise ratio near the signal source.~ By adding a few extra components, we can measure both the real and imaginary parts of the cross-correlation function--improving the overall signal-to-noise ratio by a factor of sqrt[2].~ We demonstrate the utility of our cross-correlator with noise power measurements from a quantum point contact.