Control and Detection of Singlet-Triplet Mixing in a Random Nuclear Field

TL;DR

This paper investigates singlet-triplet mixing in a double quantum dot caused by nuclear spins, demonstrating control methods and revealing a nuclear field limit on electron spin coherence time, which is vital for quantum computing.

Contribution

It provides experimental insights into controlling singlet-triplet mixing via magnetic fields and tunnel coupling, and quantifies nuclear field effects on spin coherence.

Findings

Nuclear spins cause singlet-triplet mixing in quantum dots.

Applying magnetic fields suppresses mixing.

Nuclear field fluctuations limit spin coherence time to 25 ns.

Abstract

We observe mixing between two-electron singlet and triplet states in a double quantum dot, caused by interactions with nuclear spins in the host semiconductor. This mixing is suppressed by applying a small magnetic field, or by increasing the interdot tunnel coupling and thereby the singlet-triplet splitting. Electron transport involving transitions between triplets and singlets in turn polarizes the nuclei, resulting in striking bistabilities. We extract from the fluctuating nuclear field a limitation on the time-averaged spin coherence time T2* of 25 ns. Control of the electron-nuclear interaction will therefore be crucial for the coherent manipulation of individual electron spins.