Development of Programmable Integrated Quantum Voltage Noise Source

We have been developing a Johnson noise thermometer using an integrated quantum voltage noise source (IQVNS) as a reference signal source. IQVNS is a superconducting integrated circuit that generates pseudo random signals. The power spectral density of output signal of IQVNS can be described with quantum accuracy by fundamental physical constants $e$ and h, the clock frequency of the circuit, and a numerical coefficient. In the previous version of IQVNS the numerical coefficient was fixed by the circuit design. However, to cope with the measurement of thermodynamic temperature in a wide temperature range, it is desirable to make the output of IQVNS variable. In this study, we improved part of the design of the device to be able to change the power spectral density of the output signal and confirmed by measurement that the output signal can be variable as designed.