Spin decoherence in graphene quantum dots due to hyperfine interaction

TL;DR

This paper investigates how hyperfine interactions affect electron spin coherence in graphene quantum dots, revealing anisotropic effects and decay behaviors that depend on magnetic field orientation, with implications for spin-qubit stability.

Contribution

It extends the analysis of hyperfine-induced decoherence to anisotropic interactions in graphene, providing a generalized non-Markovian framework applicable to other systems.

Findings

Electron spin coherence is preserved at high magnetic fields with small oscillations.

Decay of spin oscillations follows a power-law behavior.

Anisotropy in hyperfine interaction leads to two distinct classes affecting decoherence.

Abstract

Carbon based systems are prominent candidates for a solid-state spin-qubit due to weak spin-orbit and hyperfine interactions in combination with a low natural abundance of spin carrying isotopes. We consider the effect of the hyperfine interaction on the coherence of an electron-spin localized in a graphene quantum dot. It is known, that the hyperfine interaction in these systems is anisotropic promising interesting physics. We calculate the dynamics of an electron spin surrounded by a bath of nuclear spins in a non-Markovian approach using a generalized master equation. Considering a general form of the hyperfine interaction, we are able to extend the range of validity of our results to other systems beyond graphene. For large external magnetic fields, we find within Born approximation that the electron spin state is conserved up to small corrections, which oscillate with a frequency determined by the hyperfine interaction. The amplitude of these oscillations decays with a power law, where its initial value depends on the specific form of the anisotropy. Analyzing this in more detail, we identify two distinct classes of anisotropy, which can be both found in graphene depending on the orientation of the external magnetic field with respect to the carbon layer.