A Cryogenic Cascode Amplifier For Sensing Few Electrons Floating on Liquid Helium

As part of the 5 criteria to build a quantum computer laid out by Loss and DiVincenzo, chief among them is the ability to confine, manipulate, and measure the quantum state. Recent efforts in the electrons on helium community have pushed gate sizes on the order of an electron wavefunction and explored the confinement of electrons in such features. However, the intrinsic lack of ohmic contacts in this platform requires the use of capacitive sensing techniques to measure electron charge, making it difficult to reach the sensitivities necessary to measure single electrons without the use of carefully engineered superconducting resonators and expensive room-temperature electronics. Nonetheless, commercially available low-noise, low-input capacitance, high gain High-Electron Mobility Transistors (HEMTs) have proven to be compatible for cryogenic operation. In this talk, I will outline our efforts in building and characterizing our own bespoke cascode HEMT amplifier circuit which have since provided a meaningful path towards a low-overhead solution to sensing single electrons floating on the surface of helium.