Microscopic theory on magnetic-field-tuned sweet spot of exchange interactions in multielectron quantum-dot systems

TL;DR

This paper presents a microscopic theory showing that four-electron singlet-triplet qubits in double quantum dots can have tunable, non-monotonic exchange interactions with magnetic fields, offering potential advantages for quantum computing.

Contribution

The study reveals that four-electron singlet-triplet qubits exhibit non-monotonic exchange interactions and tunable sweet spots influenced by magnetic fields, unlike two-electron systems.

Findings

Exchange energy in four-electron qubits can be non-monotonic with detuning.

Magnetic fields can tune the position of the sweet spot.

Four-electron qubits may offer advantages for quantum computing.

Abstract

The exchange interaction in a singlet-triplet qubit defined by two-electron states in the double-quantum-dot system ("two-electron singlet-triplet qubit") typically varies monotonically with the exchange interaction and thus carries no sweet spot. Here we study a singlet-triplet qubit defined by four-electron states in the double-quantum-dot system ("four-electron singlet-triplet qubit"). We demonstrate, using configuration-interaction calculations, that in the four-electron singlet-triplet qubit the exchange energy as a function of detuning can be non-monotonic, suggesting existence of sweet spots. We further show that the tuning of the sweet spot and the corresponding exchange energy by perpendicular magnetic field can be related to the variation of orbital splitting. Our results suggest that a singlet-triplet qubit with more than two electrons can have advantages in the realization of quantum computing.