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arXiv:2602.02256

Energy-Transfer-Enhanced Emission and Quantum Sensing of VB- Defects in hBN-PbI2 Heterostructures

Eveline Mayner, Yaroslav Zhumagulov, Cristian de Giorgio, Feihong Chu, Prabhu Swain, Georg Fantner, Andras Kis, Oleg Yazyev, Aleksandra Radenovic

cond-mat.mtrl-sciphysics.opticsquant-phSubmitted Feb 2, 2026• Announced Feb 3, 2026

Abstract

Spin defects in two-dimensional materials hold significant potential for quantum information technologies and sensing applications. The negatively charged boron vacancy (VB-) in hexagonal boron nitride (hBN) has attracted considerable attention as a quantum sensor due to its demonstrated sensitivity to temperature, magnetic fields, and pressure.1 However, its applications have thus far been limited by inherently dim photoluminescence (PL). By fabricating a van der Waals heterostructure with a sensitizing donor layer, lead iodide (PbI2), we effectively enhance the PL intensity from the VB- by 5-45x, while maintaining compatibility with other heterostructures and vdW optoelectronic platforms. The type-I band alignment at the heterojunction enables efficient exciton migration while suppressing back-electron transfer, and the strong spectral overlap between the PbI2 emission and defect absorption supports efficient fluorescence resonance energy transfer. Ab initio density functional theory (DFT) predicts a photon-ratcheting mechanism that boosts absorption and emission while maintaining magnetic resonance (ODMR) contrast through minimal hybridization. Experimentally, the heterostructure exhibits enhanced continuous-wave ODMR sensitivity and functions as a precise probe of external magnetic fields. This work establishes a proof-of-concept for amplifying weak defect signals in nanomaterials, highlighting a new strategy for engineering their optical and magnetic responses.

Comments: 15 pages, 5 figures

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Spin defects in two-dimensional materials hold significant potential for quantum information technologies and sensing applications. The negatively charged boron vacancy (VB-) in hexagonal boron nitride (hBN) has attracted considerable attention as a quantum sensor due to its demonstrated sensitivity to temperature, magnetic fields, and pressure.1 However, its applications have thus far been limited by inherently dim photoluminescence (PL). By fabricating a van der Waals heterostructure with a sensitizing donor layer, lead iodide (PbI2), we effectively enhance the PL intensity from the VB- by 5-45x, while maintaining compatibility with other heterostructures and vdW optoelectronic platforms. The type-I band alignment at the heterojunction enables efficient exciton migration while suppressing back-electron transfer, and the strong spectral overlap between the PbI2 emission and defect absorption supports efficient fluorescence resonance energy transfer. Ab initio density functional theory (DFT) predicts a photon-ratcheting mechanism that boosts absorption and emission while maintaining magnetic resonance (ODMR) contrast through minimal hybridization. Experimentally, the heterostructure exhibits enhanced continuous-wave ODMR sensitivity and functions as a precise probe of external magnetic fields. This work establishes a proof-of-concept for amplifying weak defect signals in nanomaterials, highlighting a new strategy for engineering their optical and magnetic responses.

Boron vacancies (

V_B^-

) in hexagonal boron nitride (hBN) have emerged as a promising platform for two-dimensional quantum sensors capable of operating at atomic-scale proximity. However, the mechanisms responsible for photoluminescence quenching in thin hBN sensing layers when placed in contact with absorptive materials remain largely unexplored. In this Letter, we investigate non-radiative Förster resonance energy transfer (FRET) between

V_B^-

centers and either monolayer graphene or 2D semiconductors. Strikingly, we find that the FRET rate is negligible for hBN sensing layers thicker than 3 nm, highlighting the potential of

V_B^-

centers for integration into ultra-thin quantum sensors within van der Waals heterostructures. Furthermore, we experimentally extract the intrinsic radiative decay rate of

V_B^-

defects.

Negatively charged boron vacancy (

\mathrm{V_B^-}

) in hexagonal boron nitride (hBN) is the most extensively studied room-temperature quantum spin system in two-dimensional (2D) materials. Nevertheless, the current effective readout of

\mathrm{V_B^-}

spin states is carried out by systematically optical methods. This limits their exploitation in compact and miniaturized quantum devices, which would otherwise hold substantial promise to address quantum sensing and quantum information tasks. In this study, we demonstrated a photoelectric spin readout technique for

\mathrm{V_B^-}

spins in hBN. The observed photocurrent signals stem from the spin-dependent ionization dynamics of boron vacancies, mediated by spin-dependent non-radiative transitions to a metastable state. We further extend this electrical detection technique to enable the readout of dynamical decoupling sequences, including the Carr-Purcell-Meiboom-Gill (CPMG) protocols, and of nuclear spins via electron-nuclear double resonance. These results provide a pathway toward on-chip integration and real-field exploitation of quantum functionalities based on 2D material platforms.

Negatively charged boron vacancies (V

_{\text{B}}^{-}

) in hexagonal boron nitride (hBN) comprise a promising quantum sensing platform, optically addressable at room temperature and transferrable onto samples. However, broad hyperfine-split spin transitions of the ensemble pose challenges for quantum sensing with conventional resonant excitation due to limited spectral coverage. While isotopically enriched hBN using

^{10}

B and

^{15}

N isotopes (h

^{10}

B

^{15}

N) exhibits sharper spectral features, significant inhomogeneous broadening persists. We demonstrate that, implemented via frequency modulation on an FPGA, a frequency-ramped microwave pulse achieves around 4-fold greater

|0\rangle\rightarrow|-1\rangle

spin-state population transfer and thus contrast than resonant microwave excitation and thus 16-fold shorter measurement time for spin relaxation based quantum sensing. Quantum dynamics simulations reveal that an effective two-state Landau-Zener model captures the complex relationship between population inversion and pulse length with relaxations incorporated. Our approach is robust and valuable for quantum relaxometry with spin defects in hBN in noisy environments.

The negatively charged boron vacancy (${\text{VB}}^{\ensuremath{-}}$) spin defect in two-dimensional (2D) hexagonal boron nitride (

h

-BN) has attracted much attention for potential applications in quantum photonics recently. Its inherent van der Waals force mechanism guarantees convenient heterostructures for quantum sensing. By virtue of such materials, researchers not only can fabricate enough thin spin film naturally close to the sensing target but also can prepare an almost perfect spin ensemble with a uniform orientation. We here propose a setup with an ensemble of ${\text{VB}}^{\ensuremath{-}}$ spins strongly coupled to the superconducting coplanar waveguide resonator through the magnetic-dipolar interaction. The collective coupling strength is predicted to be $G/2\ensuremath{\pi}\ensuremath{\sim}15$ MHz, which corresponds to the strong coupling region. This collective spin-photon interaction can mimic the one-axis twisting Lipkin-Meshkov-Glick model effectively and therefore guarantee the dynamic generation of the spin-squeezed state. In addition, we show the influence of inhomogeneous coupling caused by sample thickness on squeezing, which proves the validity of the homogeneity assumption in our scheme. This attempt not only explores the possibility and superiority of 2D ${\text{VB}}^{\ensuremath{-}}$ spins but also opens another avenue for quantum hybridization.

Atom-like defects in hexagonal boron nitride (hBN) provide room-temperature single-photon emission and coherent spin states, making them attractive for quantum-computing and -sensing applications. However, their random spatial and spectral characteristics hamper deterministic coupling with nano-optical cavities, limiting their use as bright single-photon sources and sensitive quantum sensors. Here, we present tip-enhanced quantum-sensing spectroscopy of single-photon emitters in hBN. Through precise spatial positioning of individual emitters within tip-cavities with different plasmon resonances, we adaptively control the enhancement rates of both excitation and emission, as well as the single-photon purity. In this way, optimal selection of their relative contributions can effectively reconfigure solid-state single-photon sources, with simultaneous nano-spectroscopic space- and time-resolved analyses. Furthermore, we demonstrate tip-enhanced quantum-sensing with single spin defects through optically detected magnetic resonance (ODMR) experiments in tip-coupled hBN nanoflakes. Our approach provides a unique pathway toward highly-sensitive and deterministic quantum-sensing with room-temperature single-photon emitters.

Optically addressable spin defects in hexagonal boron nitride (hBN) are well suited for near-surface quantum sensing. They offer bright, wavelength-tunable single-photon emission with high optically detected magnetic resonance (ODMR) contrast at room temperature. Here we controllably synthesise a high density of spin-complex defects in carbon-doped hBN flakes. We find that the zero-field splitting parameter D is directly correlated with the zero-phonon line of an emitter, while the ODMR contrast shows no such correlation. We further analyse an individual narrowband defect showing 68% ODMR contrast and enhance its photon collection by ~40% using a solid immersion lens. By advancing both the practical synthesis of the spin complexes and the understanding of their microscopic origin, our results move us toward the deterministic creation of ODMR-active quantum emitters