Single-shot measurement and tunnel-rate spectroscopy of a Si/SiGe few-electron quantum dot

TL;DR

This paper studies electron tunnel rates and excited state energies in a Si/SiGe quantum dot, revealing energy-dependent tunneling and developing a rate model for understanding electron dynamics.

Contribution

It introduces a method to measure and analyze tunnel rates and excited states in Si/SiGe quantum dots, with a new rate model for quantitative understanding.

Findings

Tunnel rates are strongly energy dependent.

Excited-state energies can be directly read from charge sensing plots.

A rate model explains the relative sizes of tunnel rates.

Abstract

We investigate the tunnel rates and energies of excited states of small numbers of electrons in a quantum dot fabricated in a Si/SiGe heterostructure. Tunnel rates for loading and unloading electrons are found to be strongly energy dependent, and they vary significantly between different excited states. We show that this phenomenon enables charge sensing measurements of the average electron occupation that are analogous to Coulomb diamonds. Excited-state energies can be read directly from the plot, and we develop a rate model that enables a quantitative understanding of the relative sizes of different electron tunnel rates.