Witnessing quantum correlations in a nuclear ensemble via an electron spin qubit

• Published in: arXiv.org
• Main Authors: Gangloff, Dorian A, Zaporski, Leon, Bodey, Jonathan H, Bachorz, Clara, Jackson, Daniel M, Éthier-Majcher, Gabriel, Lang, Constantin, Clarke, Edmund, Hugues, Maxime, Claire Le Gall, Atatüre, Mete
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 19.11.2021
• Subjects: Coherence; Electron spin; Electrons; Excitation; Mean; Nuclear spin; Physics - Mesoscale and Nanoscale Physics; Physics - Quantum Physics; Quantum dots; Qubits (quantum computing)
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2012.11279

A coherent ensemble of spins interfaced with a proxy qubit is an attractive platform to create many-body coherences and probe the regime of collective excitations. An electron spin qubit in a semiconductor quantum dot can act as such an interface to the dense nuclear spin ensemble within the quantum dot consisting of multiple high-spin atomic species. Earlier work has shown that the electron can relay properties of its nuclear environment through the statistics of its mean-field interaction with the total nuclear polarisation, namely its mean and variance. Here, we demonstrate a method to probe the spin state of a nuclear ensemble that exploits its response to collective spin excitations, enabling a species-selective reconstruction beyond the mean field. For the accessible range of optically prepared mean fields, the reconstructed populations indicate that the ensemble is in a non-thermal, correlated nuclear state. The sum over reconstructed species-resolved polarisations exceeds the classical prediction threefold. This stark deviation follows from a spin ensemble that contains inter-particle coherences, and serves as an entanglement witness that confirms the formation of a dark many-body state.