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Register a new userCoupling spin defects in hexagonal boron nitride to monolithic bullseye cavities
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Color centers in hexagonal boron nitride (hBN) are becoming an increasingly important building block for quantum photonic applications. Herein, we demonstrate the efficient coupling of recently discovered spin defects in hBN to purposely designed bullseye cavities. We show that the all monolithic hBN cavity system exhibits an order of magnitude enhancement in the emission of the coupled boron vacancy spin defects. In addition, by comparative finite difference time domain modelling, we shed light on the emission dipole orientation, which has not been experimentally demonstrated at this point. Beyond that, the coupled spin system exhibits an enhanced contrast in optically detected magnetic resonance readout and improved signal to noise ratio. Thus, our experimental results supported by simulations, constitute a first step towards integration of hBN spin defects with photonic resonators for a scalable spin photon interface.
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Two-dimensional hexagonal boron nitride offers intriguing opportunities for advanced studies of light-matter interaction at the nanoscale, specifically for realizations in quantum nanophotonics. Here, we demonstrate the engineering of optically-addressable spin defects based on the negatively-charged boron vacancy center. We show that these centers can be created in exfoliated hexagonal boron nitride using a variety of focused ion beams (nitrogen, xenon and argon), with nanoscale precision. Using a combination of laser and resonant microwave excitation, we carry out optically detected magnetic resonance spectroscopy measurements, which reveal a zero-field ground state splitting for the defect of ~3.46 GHz. We also perform photoluminescence excitation spectroscopy and temperature dependent photoluminescence measurements to elucidate the photophysical properties of the center. Our results are important for advanced quantum and nanophotonics realizations involving manipulation and readout of spin defects in hexagonal boron nitride.
Development of scalable quantum photonic technologies requires on-chip integration of components such as photonic crystal cavities and waveguides with nonclassical light sources. Recently, hexagonal boron nitride (hBN) has emerged as a promising platform for nanophotonics, following reports of hyperbolic phonon-polaritons and optically stable, ultra-bright quantum emitters. However, exploitation of hBN in scalable, on-chip nanophotonic circuits, quantum information processing and cavity quantum electrodynamics (QED) experiments requires robust techniques for the fabrication of monolithic optical resonators. In this letter, we design and engineer high quality photonic crystal cavities from hBN. We employ two approaches based on a focused ion beam method and a minimally-invasive electron beam induced etching (EBIE) technique to fabricate suspended two dimensional (2D) and one dimensional (1D) cavities with quality (Q) factors in excess of 2,000. Subsequently, we show deterministic, iterative tuning of individual cavities by direct-write, single-step EBIE without significant degradation of the Q-factor. The demonstration of tunable, high Q cavities made from hBN is an unprecedented advance in nanophotonics based on van der Waals materials. Our results and hBN processing methods open up promising new avenues for solid-state systems with applications in integrated quantum photonics, polaritonics and cavity QED experiments.
Optically addressable spins in materials are important platforms for quantum technologies, such as repeaters and sensors. Identification of such systems in two-dimensional (2d) layered materials offers advantages over their bulk counterparts, as their reduced dimensionality enables more feasible on-chip integration into devices. Here, we report optically detected magnetic resonance (ODMR) from previously identified carbon-related defects in 2d hexagonal boron nitride (hBN). We show that single-defect ODMR contrast can be as strong as 6% and displays a magnetic-field dependence with both positive or negative sign per defect. This bipolarity can shed light into low contrast reported recently for ensemble ODMR measurements for these defects. Further, the ODMR lineshape comprises a doublet resonance, suggesting either low zero-field splitting or hyperfine coupling. Our results offer a promising route towards realising a room-temperature spin-photon quantum interface in hexagonal boron nitride.
Among two-dimensional atomic crystals, hexagonal boron nitride (hBN) is one of the most remarkable materials to fabricate heterostructures revealing unusual properties. We perform first-principles calculations to determine whether intercalated metal atoms and vacancies can mediate interfacial coupling and influence the structural and electronic properties of the graphene/hBN heterostructure. Metal impurity atoms (Li, K, Cr, Mn, Co, and Cu) as extrinsic defects between the graphene and hBN sheets produce $n$-doped graphene. We also consider intrinsic vacancy defects and find that a boron monovacancy in hBN act as a magnetic dopant for graphene whereas a nitrogen monovacancy in hBN serves as a nonmagnetic dopant for graphene. In contrast, smallest triangular vacancy defects in hBN are unlikely to result in significant changes in the electronic transport of graphene. Our findings reveal that the hBN layer with some vacancies or metal impurities enhance the interlayer coupling in the graphene/hBN heterostructure with respect to charge doping and electron scattering.
Optically active spin defects in wide-bandgap materials have many potential applications in quantum information and quantum sensing. Spin defects in two-dimensional layered van der Waals materials are just emerging to be investigated. Here we demonstrate that optically-addressable spin ensembles in hexagonal boron nitride (hBN) can be generated by femtosecond laser irradiation. We observe optically detected magnetic resonance (ODMR) of hBN spin defects created by laser irradiation. We show that the creation of spin defects in hBN is strongly affected by the pulse energy of the femtosecond laser. When the laser pulse number is less than a few thousand, the pulse number only affects the density of defects but not the type of defects. With proper laser parameters, spin defects can be generated with a high probability of success. Our work provides a convenient way to create spin defects in hBN by femtosecond laser writing, which shows promising prospects for quantum technologies.
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