Enhanced spin coherence at the sweet spot of a self-assembled quantum dot molecule

TL;DR

This study demonstrates significantly enhanced spin coherence times in a self-assembled quantum dot molecule at the electrical bias sweet spot, revealing key dephasing mechanisms affecting quantum coherence.

Contribution

First direct measurement of $T_2^*$ coherence time in self-assembled quantum dot molecules at the sweet spot, showing over tenfold increase compared to single dots.

Findings

Maximum $T_2^*$ of 60 ns achieved

Electrical noise and nuclear spin interactions identified as main dephasing sources

Spin coherence is optimized at the electrical bias sweet spot

Abstract

A pair of coupled dots with one electron in each dot can provide improvements in spin coherence, particularly at an electrical bias called the sweet spot, but few measurements have been performed on self-assembled dots in this regime. Here, we directly measure the $T_2^*$ coherence time of the singlet-triplet states in this system as a function of bias and magnetic field, obtaining a maximum $T_2^*$ of 60 ns, more than an order of magnitude higher than an electron spin in a single quantum dot. Our results uncover two main dephasing mechanisms: electrical noise away from the sweet spot, and a magnetic field dependent interaction with nuclear spins due to a difference in g-factors.