Confining Electrons on Helium in Quantum Dots

Abstract

Quantum computing with electron spins requires the precise manipulation and detectionof the electron charge state. Electrons on helium has lacked in this regard, opting to use deep channel, micron sized gates to address electrons while utilizing exotic methods for electron sensing. This thesis focuses on the feasibility of trapping and controlling electrons in sub- micron quantum dots, developing an all-electrical cryogenic amplifier circuit for electron sensing, transporting small packets of electrons over thin helium films, and measuring the spin degree of freedom of 109 spins over superfluid helium. The first portion of the thesis describes an experiment exploring the use of an array of750,000 dual layer lithographically defined 200 nanometer quantum dots to trap electrons. We find that these quantum dots can support 10s of electrons but also acknowledge that a change in device structure needs to be made to allow for more experimental repeatability. In the end, this experiment highlighted the need to transition to thin film devices and more sensitive measurement techniques. The second portion of this thesis focuses on a novel device design that allows for a gentletransition between thick and thin helium films. The use of a smooth amorphous resistive metal allows us to drive electrons across the thin helium surface with reasonable voltages; and by integrating this with our take on a cryogenic amplifier circuit using High Electron Mobility Transistors, we can measure the mobilities of small packets of electrons. We find that these results are in good agreement with previous measurements of mobilities of many (millions) electrons over bulk helium films at the temperatures we work in. The last portion of this thesis details our attempt to measure the spin coherence andlifetimes of electrons floating on helium using a 3D Cavity. The complexities associated with integrating these two wildly different systems together required a novel approach to sample motion at cryogenic temperatures. We detail the thought process and implementation of this new setup that preserves over 95% of 2 inches of room temperature motion at cryogenic temperatures.