Single-shot readout of a solid-state spin in a decoherence-free subspace

TL;DR

This paper proposes a two-stage optical and microwave protocol for single-shot spin readout in quantum dot molecules' decoherence-free subspace, achieving over 97% fidelity with realistic photon collection efficiency, advancing quantum network components.

Contribution

It introduces a novel two-stage spin readout protocol that enhances fidelity and efficiency in quantum dot molecules' decoherence-free subspace, enabling practical quantum information applications.

Findings

Achieves over 97% spin readout fidelity.

Demonstrates feasibility with 0.12% photon collection efficiency.

Enables single-shot readout in realistic conditions.

Abstract

The efficient single photon emission capabilities of quantum dot molecules position them as promising platforms for quantum information processing. Furthermore, quantum dot molecules feature a "decoherence-free" subspace that enables spin qubits with long coherence time. To efficiently read out the spin state within this subspace requires optically cycling isolated transitions that originate from a triplet manifold within the quantum dot molecule. We propose and theoretically study a two-stage spin readout protocol within this decoherence-free subspace that allows single-shot readout performance. The process incorporates a microwave $\pi$-pulse and optically cycling the isolated transitions, which induces fluorescence that allows us to identify the initial spin state. This protocol offers enhanced readout fidelity compared to previous schemes that rely on the excitation of transitions that strongly decay to multiple ground states or require long initialization via slow, optically forbidden transitions. By simulating the performance of the protocol, we show that an optimal spin readout fidelity of over 97% and single-shot readout performance are achievable for a photon collection efficiency of just 0.12%. This high readout performance for such realistic photon collection conditions within the decoherence-free subspace expands the potential of quantum dot molecules as building blocks for quantum networks.