Calculation of tunnel-couplings in open gate-defined disordered quantum dot systems

TL;DR

This paper introduces a Green's formalism method to accurately calculate tunnel-couplings in disordered quantum dot systems, accounting for electrostatic potential and disorder effects crucial for scalable quantum computing.

Contribution

It develops a detailed computational approach for tunnel-coupling calculation that includes potential disorder, advancing the design and tuning of quantum dot devices.

Findings

Charged defects cause four orders of magnitude variation in tunnel-couplings.

The method accurately models electrostatic potentials and disorder effects.

Disorder significantly impacts tunnel-coupling in large-scale silicon qubits.

Abstract

Quantum computation based on semiconductor electron-spin qubits requires high control of tunnel-couplings, both across quantum dots and between the quantum dot and the reservoir. The tunnel-coupling to the reservoir sets the qubit detection and initialization bandwidth for energy-resolved spin-to-charge conversion and is essential to tune single-electron transistors commonly used as charge detectors. Potential disorder and the increasing complexity of the two-dimensional gate-defined quantum computing devices sets high demands on the gate design and the voltage tuning of the tunnel barriers. We present a Green's formalism approach for the calculation of tunnel-couplings between a quantum dot and a reservoir. Our method takes into account in full detail the two-dimensional electrostatic potential of the quantum dot, the tunnel barrier and reservoir. A Markov approximation is only employed far away from the tunnel barrier region where the density of states is sufficiently large. We calculate the tunnel-coupling including potential disorder effects, which become increasingly important for large-scale silicon-based spin-qubit devices. Studying the tunnel-couplings of a single-electron transistor in Si/SiGe as a showcase, we find that charged defects are the dominant source of disorder leading to variations in the tunnel-coupling of four orders of magnitude.