Theory of barrier vs tilt exchange gate operations in spin-based quantum computing

TL;DR

This paper develops a theoretical framework to compare barrier and tilt gate control methods for exchange interactions in spin-based quantum dots, highlighting advantages of barrier control for gate fidelity and noise resilience.

Contribution

It introduces a comprehensive theory combining Hubbard and confining-potential models to explain why barrier gates outperform tilt gates in quantum dot spin qubits.

Findings

Barrier control reduces sensitivity to charge noise.

Exchange coupling can be optimized at a sweet spot with zero derivative.

Qualitative agreement with experimental data for GaAs and Si quantum dots.

Abstract

We present a theory for understanding the exchange interaction between electron spins in neighboring quantum dots, either by changing the detuning of the two quantum dots or independently tuning the tunneling barrier between quantum dots. The Hubbard model and a more realistic confining-potential model are used to investigate how the tilting and barrier control affect the effective exchange coupling and thus the gate fidelity in both the detuning and symmetric regimes. We show that the exchange coupling is less sensitive to the charge noise through tunnel barrier control (while allowing for exchange coupling operations on a sweet spot where the exchange interaction has zero derivative with respect to the detuning). Both GaAs and Si quantum dots are considered and we compare our results with experimental data showing qualitative agreements. Our results answer the open question of why barrier gates are preferable to tilt gates for exchange-base gate operations.