Relaxation and Readout Visibility of a Singlet-Triplet Qubit in an Overhauser Field Gradient

TL;DR

This study examines how dynamic nuclear polarization affects the Overhauser field gradient, spin relaxation, and readout visibility of a singlet-triplet qubit in a GaAs quantum dot, revealing that increased gradients reduce T_1 and visibility.

Contribution

It provides a detailed experimental and theoretical analysis of how DNP influences qubit relaxation and readout, highlighting the impact of Overhauser field gradients on qubit performance.

Findings

DNP increases Overhauser field gradients at fields up to 2 T.

Increased gradients decrease T_1 and reduce readout visibility.

A relaxation model aligns well with experimental results.

Abstract

Using single-shot charge detection in a GaAs double quantum dot, we investigate spin relaxation time T_1 and readout visibility of a two-electron singlet-triplet qubit following single-electron dynamic nuclear polarization (DNP). For magnetic fields up to 2 T, the DNP cycle is in all cases found to increase Overhauser field gradients, which in turn decrease T_1 and consequently reduce readout visibility. This effect was previously attributed to a suppression of singlet-triplet dephasing under a similar DNP cycle. A model describing relaxation after singlet-triplet mixing agrees well with experiment. Effects of pulse bandwidth on visibility are also investigated.