Stable Voltage Generation With a Josephson Voltage Standard Device Cooled at a 4 K Stage in a Dilution Refrigerator

We have demonstrated voltage generation in a dilution refrigerator using a Josephson voltage standard (JVS). A niobium-nitride (NbN)-based superconductor-normal metal-superconductor Josephson junction (JJ) array was placed hung directly under the 4 K stage of the dilution refrigerator. The thermal design of wiring was optimized to achieve stable operation of the JVS and temperature stability of the 4 K stage. After that, we measured the flatness of the quantized voltage steps. We obtained the combined relative uncertainty of
$2.4\times 10^{-10}$
V/V within 40 min of accumulation and
$2.1\times 10^{-8}$
V/V within 13 h of accumulation for 1028 and 2 mV generation, respectively.