Thèse Spectroscopie de Défauts de Spin Optiquement Actifs à Température Sub-Kelvin H/F - Doctorat.Gouv.Fr

Établissement : Université de Montpellier École doctorale : I2S - Information, Structures, Systèmes Laboratoire de recherche : L2C - Laboratoire Charles Coulomb Direction de la thèse : Vincent JACQUES ORCID 0000000154716061 Début de la thèse : 2026-10-01 Date limite de candidature : 2026-07-15T23:59:59 Un des objectifs important de la thèse est le développement d'un nouveau dispositif expérimental intégrant un microscope optique confocal à balayage dans un cryostat à dilution permettant d'atteindre une température de base d'environ 5 mK. Cette plateforme expérimentale sera également dotée d'un système d'excitation radiofréquence afin de réaliser des expériences de spectroscopie de spin par détection optique de la résonance magnétique. Ce dispositif expérimental sera utilisé durant la thèse pour l'étude de défauts ponctuels dans le nitrure de bore hexagonal (hBN) et dans le silicium, pour des applications dans les domaines des capteurs et des communications quantiques. Optically-active spin defects in semiconductors are currently attracting considerable interest in the growing field of quantum technologies [1]. These point defects, which feature localized electronic states with energy levels buried inside the bandgap of the host material, behave as artificial atoms nestled in a solid. Once isolated at the individual scale, such quantum systems can be first employed as solid-state single photon sources for quantum communications [2]. Importantly, the electronic spin of the defect can offer an additional quantum resource, either for the realization of advanced quantum information protocols relying on a spin/photon interface [3], or for quantum sensing purposes [4]. To date, the most advanced solid-state platform for quantum technologies is undoubtedly the nitrogen-vacancy (NV) color center in diamond [5]. However, the search for alternative materials that could expand the range of functionalities offered by diamond remains a very active field of research worldwide. In this context, the team Solid-state quantum technologies (S2QT) at Laboratoire Charles Coulomb (L2C, Montpellier) explores the physics of optically-active spin defects in silicon and hexagonal boron nitride (hBN). On one hand, silicon is the flagship material of the semiconductor industry offering unique prospects for large-scale nano-fabrication processes. On the other hand, hBN is currently the most promising material for the development of quantum sensing technologies on a two-dimensional (2D) platform. The PhD project will focus on investigating the optical and spin properties of these defects at sub-kelvin temperatures, a regime that remains largely unexplored and offers unique opportunities to uncover new physical phenomena and enhance their performance for quantum technology applications.

So far, the optical and spin properties of point defects in silicon and hBN have been only explored at temperatures ranging from 300 K to 4K. The main goal of PhD project is to extend these studies in a dilution refrigerator with a base temperature of 30 mK. To this end, a scanning confocal microscope with single defect sensitivity and microwave excitation facilities for coherent spin manipulation will be integrated in a dilution fridge. This is a highly challenging experimental task, which has only been carried out by a few research groups studying color centers in diamond [6,7]. Given the unavoidable heating induced by laser and microwave excitations, our objective is to perform measurements at few hundreds of mK. As an example of the impact of such a temperature environment, it was recently shown that the spin coherence time of point defects in diamond (GeV, SiV) can be increased by several orders of magnitude by reducing the temperature from 4 K to 200 mK, thanks to an efficient suppression of phonon-induced relaxation processes [7]. These results motivate the study of solid-state spin defects at sub-K temperature in order to enhance their performances for quantum technologies.

In this PhD project, we will analyse how the optical and spin coherence properties of point defects in silicon and hBN evolve at sub-K temperatures. For defects in silicon, the long-term goal is to develop an efficient spin/photon interface for quantum communication networks. For defects in hBN, we will focus on their performances for quantum sensing applications. The long-term goal is to study the physics of 2D superconductors by local measurements of the Meissner effect with a hBN-based quantum sensing unit integrated in van der Waals heretostructure.

[1] D. D. Awschalom, R. Hanson, J. Wrachtrup and B. B. Zhou, Quantum technologies with optically
interfaced solid-state spins, Nat. Phot. 12, 507 (2018).
[2] I. Aharonovich, et al., Solid-state single-photon emitters, Nat. Phot. 10, 631 (2016).
[3] B. Hensen et al., Loophole-free Bell inequality violation using electron spins separated by 1.3
kilometres, Nature 526, 682 (2015).
[4] C. L. Degen et al., Quantum sensing, Rev. Mod. Phys. 89, 035002 (2017).
[5] M. W Doherty et al., The nitrogen-vacancy colour centre in diamond, Phys. Rep. 528, 1-45
(2013).
[6] D. D. Sukachev et al., Silicon-vacancy spin qubit in diamond: A quantum memory exceeding 10
ms with single-shot state readout, Phys. Rev. Lett. 119, 223602 (2017).
[7] K. Senkalla et al., Germanium Vacancy in Diamond Quantum Memory Exceeding 20 ms, Phys.
Rev. Lett. 132, 026901 (2024).

- Connaissances solides en physique quantique et en technologies quantiques.
- Bonne maîtrise de l'Anglais parlé, lu et écrit.
- Bonnes compétences en communication et capacité de travailler en équipe.