Second Quantization: Gating a Quantum Dot Through the Sequential Removal of Single Electrons from a Nanoscale Floating Gate

TL;DR

This paper demonstrates a method to control and measure charge states in a nanoscale quantum dot using an AFM tip as a cryogenic switch, revealing discrete charge steps and an extremely high leakage resistance.

Contribution

It introduces a novel technique employing an AFM tip to precisely manipulate and measure charge in a quantum dot floating gate at nanometer scale.

Findings

Charge changes occur in discrete steps.

Leakage resistance estimated at ~10^19 Ohms.

Quantum dot size reduced to ~100 nm.

Abstract

We use the tip of an atomic force microscope (AFM) to charge floating metallic gates defined on the surface of a Si/SiGe heterostructure. The AFM tip serves as an ideal and movable cryogenic switch, allowing us to bias a floating gate to a specific voltage and then lock the charge on the gate by withdrawing the tip. Biasing with an AFM tip allows us to reduce the size of a quantum dot floating gate electrode down to $\sim100~\mathrm{nm}$. Measurements of the conductance through a quantum dot formed beneath the floating gate indicate that its charge changes in discrete steps. From the statistics of the single-electron leakage events, we determine the floating gate leakage resistance $R \sim 10^{19}~ \mathrm{Ohm}$ - a value immeasurable by conventional means.