Extracting inter-dot tunnel couplings between few donor quantum dots in silicon

TL;DR

This paper presents a novel method to accurately measure the tunnel coupling between quantum dots in silicon, which is crucial for scaling solid-state quantum computing architectures, demonstrated on donor triple quantum dots with precise extraction of coupling values.

Contribution

The authors introduce a new technique utilizing differential tunnel rates to a reservoir for extracting tunnel couplings in quantum dot systems, validated on silicon donor triple quantum dots.

Findings

Successfully measured tunnel couplings of 5.5 GHz and 2.2 GHz.

Technique works even when tunnel coupling is below electron temperature.

Provides a reliable characterization method for multi-dot quantum devices.

Abstract

The long term scaling prospects for solid-state quantum computing architectures relies heavily on the ability to simply and reliably measure and control the coherent electron interaction strength, known as the tunnel coupling, $t_c$. Here, we describe a method to extract the $t_c$ between two quantum dots (QDs) utilising their different tunnel rates to a reservoir. We demonstrate the technique on a few donor triple QD tunnel coupled to a nearby single-electron transistor (SET) in silicon. The device was patterned using scanning tunneling microscopy-hydrogen lithography allowing for a direct measurement of the tunnel coupling for a given inter-dot distance. We extract ${t}_{{\rm{c}}}=5.5\pm 1.8\;{\rm{GHz}}$ and ${t}_{{\rm{c}}}=2.2\pm 1.3\;{\rm{GHz}}$ between each of the nearest-neighbour QDs which are separated by 14.5 nm and 14.0 nm, respectively. The technique allows for an accurate measurement of $t_c$ for nanoscale devices even when it is smaller than the electron temperature and is an ideal characterisation tool for multi-dot systems with a charge sensor.