Effects of charge noise on a pulse-gated singlet-triplet $S-T_-$ qubit

TL;DR

This paper investigates how charge noise affects the coherence and visibility of quantum oscillations in a pulse-gated singlet-triplet qubit, proposing tuning strategies to mitigate decoherence.

Contribution

The study combines experimental data with a theoretical model to explain charge noise effects and suggests tuning interdot tunneling to improve qubit visibility.

Findings

Charge noise causes decoherence near the singlet-triplet avoided crossing.

Quantum oscillation visibility is low near charge degeneracy points.

Proper tuning of interdot tunneling can significantly enhance visibility.

Abstract

We study the dynamics of a pulse-gated semiconductor double quantum dot qubit. In our experiments, the qubit coherence times are relatively long, but the visibility of the quantum oscillations is low. We show that these observations are consistent with a theory that incorporates decoherence arising from charge noise that gives rise to detuning fluctuations of the double dot. Because effects from charge noise are largest near the singlet-triplet avoided level crossing, the visibility of the oscillations are low when the singlet-triplet avoided level crossing occurs in the vicinity of the charge degeneracy point crossed during the manipulation, but there is only modest dephasing at the large detuning value at which the quantum phase accumulates. This theory agrees well with experimental data and predicts that the visibility can be increased greatly by appropriate tuning of the interdot tunneling rate.