Spin measurement using cycling transitions of a two-electron quantum dot molecule

TL;DR

This paper demonstrates an improved optical read-out method for a singlet-triplet qubit in a two-electron quantum dot molecule using cycling transitions, significantly enhancing measurement fidelity.

Contribution

It introduces a novel spin measurement technique leveraging cycling transitions from auxiliary states, enabling near two-orders-of-magnitude fidelity improvement.

Findings

Achieved high-fidelity spin read-out via cycling transitions.

Implemented spin-selective state transfer with a resonant laser.

Potential for single-shot qubit read-out in micro-cavity structures.

Abstract

Two-electron charged self-assembled quantum dot molecules exhibit a decoherence-avoiding singlet-triplet qubit subspace and an efficient spin-photon interface. Here, we demonstrate that the cycling transitions originating from auxiliary ground states in the same system allow for an efficient optical read-out of a singlet-triplet qubit. By implementing a spin-selective state transfer to the auxiliary state using a resonant laser field, we observe an improvement approaching two orders of magnitude in fidelity as compared to spin measurement by light scattering directly from the qubit states. Embedding the quantum dot molecule inside a low quality-factor micro-cavity structure should enable single-shot qubit read-out.