Quantum dots and spin qubits in graphene

TL;DR

This review explores the potential of graphene quantum dots as hosts for spin qubits, discussing their advantages, challenges, and methods for manipulating spins and overcoming valley degeneracy issues.

Contribution

It provides a detailed analysis of gate-tunable graphene quantum dots, including calculations of bound states and strategies to break valley degeneracy for spin qubit applications.

Findings

Graphene quantum dots can be engineered with different architectures for spin qubits.

Valley degeneracy can be broken using specific terminations or magnetic fields.

Spin decoherence mechanisms include spin-orbit interaction, electron-phonon coupling, and hyperfine interactions.

Abstract

This is a review on graphene quantum dots and their use as a host for spin qubits. We discuss the advantages but also the challenges to use graphene quantum dots for spin qubits as compared to the more standard materials like GaAs. We start with an overview of this young and fascinating field and will then discuss gate-tunable quantum dots in detail. We calculate the bound states for three different quantum dot architectures where a bulk gap allows for confinement via electrostatic fields: (i) graphene nanoribbons with armchair boundary, (ii) a disc in single-layer graphene, and (iii) a disc in bilayer graphene. In order for graphene quantum dots to be useful in the context of spin qubits, one needs to find reliable ways to break the valley-degeneracy. This is achieved here, either by a specific termination of graphene in (i) or in (ii) and (iii) by a magnetic field, without the need of a specific boundary. We further discuss how to manipulate spin in these quantum dots and explain the mechanism of spin decoherence and relaxation caused by spin-orbit interaction in combination with electron-phonon coupling, and by hyperfine interaction with the nuclear spin system.