Cryogenic amplifier with low input-referred voltage noise calibrated by shot noise measurement

A low-noise cryogenic amplifier for the bandwidth from 100 kHz to 2 MHz with commercially available components is presented. The amplifier is mounted on the cold finger of our home-made liquid helium dipstick. The input impedance of the amplifier is 2 kΩ. The input-referred voltage noise of the amplifier at approximately 2 MHz is around 1 nV/√Hz. We demonstrate the performance of the amplifier by measuring shot noise on the Al/AlO_x/Al tunneling junction with resistance about 17 kΩ at liquid helium temperature.