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1. Isotope engineering for spin defects in van der Waals materials

   https://doi.org/10.1038/s41467-023-44494-3  

   Gong, Ruotian; Du, Xinyi; Janzen, Eli; Liu, Vincent; Liu, Zhongyuan; He, Guanghui; Ye, Bingtian; Li, Tongcang; Yao, Norman Y; Edgar, James H; et al (December 2024, Nature Communications)

   Abstract Spin defects in van der Waals materials offer a promising platform for advancing quantum technologies. Here, we propose and demonstrate a powerful technique based on isotope engineering of host materials to significantly enhance the coherence properties of embedded spin defects. Focusing on the recently-discovered negatively charged boron vacancy center ($${{{{{{{{\rm{V}}}}}}}}}_{{{{{{{{\rm{B}}}}}}}}}^{-}$$ $V_B^{-}$ ) in hexagonal boron nitride (hBN), we grow isotopically purified h¹⁰B¹⁵N crystals. Compared to$${{{{{{{{\rm{V}}}}}}}}}_{{{{{{{{\rm{B}}}}}}}}}^{-}$$ $V_B^{-}$ in hBN with the natural distribution of isotopes, we observe substantially narrower and less crowded$${{{{{{{{\rm{V}}}}}}}}}_{{{{{{{{\rm{B}}}}}}}}}^{-}$$ $V_B^{-}$ spin transitions as well as extended coherence timeT₂and relaxation timeT₁. For quantum sensing,$${{{{{{{{\rm{V}}}}}}}}}_{{{{{{{{\rm{B}}}}}}}}}^{-}$$ $V_B^{-}$ centers in our h¹⁰B¹⁵N samples exhibit a factor of 4 (2) enhancement in DC (AC) magnetic field sensitivity. For additional quantum resources, the individual addressability of the$${{{{{{{{\rm{V}}}}}}}}}_{{{{{{{{\rm{B}}}}}}}}}^{-}$$ $V_B^{-}$ hyperfine levels enables the dynamical polarization and coherent control of the three nearest-neighbor¹⁵N nuclear spins. Our results demonstrate the power of isotope engineering for enhancing the properties of quantum spin defects in hBN, and can be readily extended to improving spin qubits in a broad family of van der Waals materials. 

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2. Dielectric Environment Sensitivity of Carbon Centers in Hexagonal Boron Nitride

   https://doi.org/10.1002/smll.202300144  

   Badrtdinov, Danis I.; Rodriguez‐Fernandez, Carlos; Grzeszczyk, Magdalena; Qiu, Zhizhan; Vaklinova, Kristina; Huang, Pengru; Hampel, Alexander; Watanabe, Kenji; Taniguchi, Takashi; Jiong, Lu; et al (October 2023, Small)

   Abstract A key advantage of utilizing van‐der‐Waals (vdW) materials as defect‐hosting platforms for quantum applications is the controllable proximity of the defect to the surface or the substrate allowing for improved light extraction, enhanced coupling with photonic elements, or more sensitive metrology. However, this aspect results in a significant challenge for defect identification and characterization, as the defect's properties depend on the the atomic environment. This study explores how the environment can influence the properties of carbon impurity centers in hexagonal boron nitride (hBN). It compares the optical and electronic properties of such defects between bulk‐like and few‐layer films, showing alteration of the zero‐phonon line energies and their phonon sidebands, and enhancements of inhomogeneous broadenings. To disentangle the mechanisms responsible for these changes, including the atomic structure, electronic wavefunctions, and dielectric screening, it combines ab initio calculations with a quantum‐embedding approach. By studying various carbon‐based defects embedded in monolayer and bulk hBN, it demonstrates that the dominant effect of the change in the environment is the screening of density–density Coulomb interactions between the defect orbitals. The comparative analysis of experimental and theoretical findings paves the way for improved identification of defects in low‐dimensional materials and the development of atomic scale sensors for dielectric environments. 

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3. Wide field imaging of van der Waals ferromagnet Fe3GeTe2 by spin defects in hexagonal boron nitride

   https://doi.org/10.1038/s41467-022-33016-2  

   Huang, Mengqi; Zhou, Jingcheng; Chen, Di; Lu, Hanyi; McLaughlin, Nathan J.; Li, Senlei; Alghamdi, Mohammed; Djugba, Dziga; Shi, Jing; Wang, Hailong; et al (December 2022, Nature Communications)

   Abstract Emergent color centers with accessible spins hosted by van der Waals materials have attracted substantial interest in recent years due to their significant potential for implementing transformative quantum sensing technologies. Hexagonal boron nitride (hBN) is naturally relevant in this context due to its remarkable ease of integration into devices consisting of low-dimensional materials. Taking advantage of boron vacancy spin defects in hBN, we report nanoscale quantum imaging of low-dimensional ferromagnetism sustained in Fe 3 GeTe 2 /hBN van der Waals heterostructures. Exploiting spin relaxometry methods, we have further observed spatially varying magnetic fluctuations in the exfoliated Fe 3 GeTe 2 flake, whose magnitude reaches a peak value around the Curie temperature. Our results demonstrate the capability of spin defects in hBN of investigating local magnetic properties of layered materials in an accessible and precise way, which can be extended readily to a broad range of miniaturized van der Waals heterostructure systems. 

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4. First-principles computational methods for quantum defects in two-dimensional materials: A perspective

   https://doi.org/10.1063/5.0230736  

   Seo, Hosung; Ivády, Viktor; Ping, Yuan (September 2024, Applied Physics Letters)

   Quantum defects are atomic defects in materials that provide resources to construct quantum information devices such as single-photon emitters and spin qubits. Recently, two-dimensional (2D) materials gained prominence as a host of quantum defects with many attractive features derived from their atomically thin and layered material formfactor. In this Perspective, we discuss first-principles computational methods and challenges to predict the spin and electronic properties of quantum defects in 2D materials. We focus on the open quantum system nature of the defects and their interaction with external parameters such as electric field, magnetic field, and lattice strain. We also discuss how such prediction and understanding can be used to guide experimental studies, ranging from defect identification to tuning of their spin and optical properties. This Perspective provides significant insights into the interplay between the defect, the host material, and the environment, which will be essential in the pursuit of ideal two-dimensional quantum defect platforms. 

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5. Coherent Control of Nitrogen Nuclear Spins via the VB−‐Center in Hexagonal Boron Nitride

   https://doi.org/10.1002/adfm.202524710  

   Tibiássy, Adalbert; Patrickson, Charlie J; Poirier, Thomas; Edgar, James H; Lopez‐Rodriguez, Bruno; Ivády, Viktor; Luxmoore, Isaac J (April 2026, Advanced Functional Materials)

   ABSTRACT Charged boron vacancies () in hexagonal boron nitride (hBN) have emerged as a promising platform for quantum nanoscale sensing and imaging. While these primarily involve electron spins, nuclear spins provide an additional resource for quantum operations. This work presents a comprehensive experimental and theoretical study of the properties and coherent control of the nearest‐neighbor nuclear spins of ‐ensembles in isotope‐enriched . Multi‐nuclear spin states are selectively addressed, enabled by the state‐specific nuclear spin transitions arising from spin‐state mixing. We perform Rabi driving between selected state pairs, define elementary quantum gates, and measure longer than 10  nuclear Rabi coherence times. We observe a two orders of magnitude nuclear g‐factor enhancement that underpins fast nuclear spin gates. Accompanying numerical simulations provide a deep insight into the underlying mechanisms. These results establish the foundations for leveraging nuclear spins in center‐based quantum applications, particularly for extending coherence times and enhancing the sensitivity of 2D quantum sensing foils. 

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