Sensing Few Electrons Floating on Helium with High-Electron-Mobility Transistors

Abstract

We report on low-frequency measurements of few electrons floating on superfluid helium using a bespoke cryogenic cascode amplifier circuit built with off-the-shelf GaAs high-electron-mobility transistors (HEMTs). We integrate this circuit with a charge-coupled device (CCD) to transport the electrons on helium and characterize its performance. We show that this circuit has a signal-to-noise ratio (SNR) of \(\thicksim\) 2\(\frac{e}{\sqrt{Hz}}\) at 102 kHz, an order of magnitude improvement from previous implementations, and provides a compelling alternative to few electron sensing with high-frequency resonators.