Charge noise, spin-orbit coupling, and coherence of single-spin qubits

TL;DR

This paper derives a Hamiltonian to describe how spin-orbit coupling and charge noise affect single-spin qubits in quantum dots, highlighting how material choice and device design influence coherence times.

Contribution

It provides a detailed theoretical model linking charge noise, spin-orbit effects, and qubit decoherence, with insights into optimizing materials and device parameters for better coherence.

Findings

Relaxation is mainly caused by noise coupling different orbital levels.

Dephasing is driven by charge defects and varies significantly between Si and GaAs.

Coherence times can be improved by material choice and device engineering.

Abstract

Spin-orbit coupling is ubiquitous in quantum dot quantum computing architectures, and makes spin qubits susceptible to charge noise. We derive a Hamiltonian describing the effect of spin-orbit and noise on a single-spin qubit in a quantum dot. Relaxation is due to noise coupling different orbital levels and is dominated by screened whole charge defects near the dot. Dephasing stems from noise causing relative fluctuations between orbital levels, and is driven by screened whole charge defects and unscreened dipole defects in the substrate. Dephasing times are vastly different between common materials such as Si and GaAs. They can be enhanced by increasing gate fields, choosing materials with weak spin-orbit such as Si, making dots narrower, or using accumulation dots.