Extended Data Fig. 4: HEMT noise characterization.
From: A cryogenic electro-optic interconnect for superconducting devices
a, Experimental setup and schematic signal flow. A noise source thermalized at temperature T feeds the HEMT with Johnson noise. The measured power spectral density is proportional to the noise from the source plus the HEMT added noise. The noise source is a thermally isolated copper block containing a cryogenic resistive heater, a thermometer, and a 50Ω load. The noise source is connected to a 12 GHz low-pass filter. b, The added noise of the HEMT versus frequency. Inset: An example of the measured power spectral density at 6 GHz vs. T. The dashed line is to a fit Eq. (11).
