Extended orbital modeling of spin qubits in double quantum dots

TL;DR

This paper presents an extended orbital model for spin qubits in double quantum dots, incorporating excited orbitals to better understand exchange coupling dynamics and match experimental measurements.

Contribution

An extended Hund Mulliken model including excited orbitals is developed, enhancing the accuracy and analytical tractability of orbital modeling for spin qubits.

Findings

Model agrees with recent exchange measurements at high bias

Reduced sensitivity to bias fluctuations in exchange coupling

Maintains large exchange for fast quantum gating

Abstract

Orbital modeling of two electron spins confined in a double quantum dot is revisited. We develop an extended Hund Mulliken approach that includes excited orbitals, allowing for a triplet configuration with both electrons residing in a single dot. This model improves the reliability and applicability of the standard Hund Mulliken approximation, while remaining largely analytical, thus it enables us to identify the mechanisms behind the exchange coupling dynamics that we find. In particular, our calculations are in close agreement with exchange values that were recently measured at a high interdot bias regime, where the double occupancy triplet configuration is energetically accessible, demonstrating reduced sensitivity to bias fluctuations, while maintaining the large exchange needed for fast gating.