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Register a new userSpin-Dependent Quantum Emission in Hexagonal Boron Nitride at Room Temperature
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Optically addressable spins associated with defects in wide-bandgap semiconductors are versatile platforms for quantum information processing and nanoscale sensing, where spin-dependent inter-system crossing (ISC) transitions facilitate optical spin initialization and readout. Recently, the van der Waals material hexagonal boron nitride (h-BN) has emerged as a robust host for quantum emitters (QEs), but spin-related effects have yet to be observed. Here, we report room-temperature observations of strongly anisotropic photoluminescence (PL) patterns as a function of applied magnetic field for select QEs in h-BN. Field-dependent variations in the steady-state PL and photon emission statistics are consistent with an electronic model featuring a spin-dependent ISC between triplet and singlet manifolds, indicating that optically-addressable spin defects are present in h-BN $-$ a versatile two-dimensional material promising efficient photon extraction, atom-scale engineering, and the realization of spin-based quantum technologies using van der Waals heterostructures.
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Two-dimensional hexagonal boron nitride (hBN) has attracted large attentions as platforms for realizations for integrated nanophotonics and collective effort has been focused on the spin defect centers. Here, the temperature dependence of the resonance spectrum in the range of 5-600 K is investigated. The zero-field splitting (ZFS) parameter D is found to decrease monotonicly with increasing temperature and can be described by Varshni empirical equation perfectly, while E almost does not change. We systematically study the differences among different hBN nanopowders and provide an evidence of edge effects on ODMR of VB- defects. Considering the proportional relation between D and reciprocal of lattice volume, the thermal expansion might be the dominant reason for energy-level shifts. We also demonstrate that the VB- defects still exist stably at least at 600 K. Moreover, we propose a scheme for detecting laser intensity using the VB- defects in hBN nanopowders, which is based on the obvious dependence of its D value on laser intensity. Our results are helpful to gain insight into the spin properties of VB- and for the realizations of miniaturized, integrated thermal sensor.
Optically active defects in solids with accessible spin states are promising candidates for solid state quantum information and sensing applications. To employ these defects as quantum building blocks, coherent manipulation of their spin state is required. Here we realize coherent control of ensembles of boron vacancy (V$_B^-$) centers in hexagonal boron nitride (hBN). Specifically, by applying pulsed spin resonance protocols, we measure spin-lattice relaxation time ($T_1$) of 18 $mu$s and spin coherence time ($T_2$) of 2 $mu$s at room temperature. The spin-lattice relaxation time increases by three orders of magnitude at cryogenic temperature. Furthermore, employing a two- and three-pulse electron spin-echo envelope modulation (ESEEM) we separate the quadrupole and hyperfine interactions with the surrounding nuclei. Finally, by applying a method to decouple the spin state from its inhomogeneous nuclear environment - a hole-burning - the spectral optically detected magnetic resonance linewidth is significantly reduced to several tens of kHz, thus extending the spin coherence time by a factor of three. Our results are important for employment of van der Waals materials for quantum technologies, specifically in the context of using hBN as a high-resolution quantum sensor for hybrid quantum systems including 2D heterostructures, nanoscale devices and emerging atomically thin magnets.
Atomically thin van der Waals crystals have recently enabled new scientific and technological breakthroughs across a variety of disciplines in materials science, nanophotonics and physics. However, non-classical photon emission from these materials has not been achieved to date. Here we report room temperature quantum emission from hexagonal boron nitride nanoflakes. The single photon emitter exhibits a combination of superb quantum optical properties at room temperature that include the highest brightness reported in the visible part of the spectrum, narrow line width, absolute photo-stability, a short excited state lifetime and a high quantum efficiency. Density functional theory modeling suggests that the emitter is the antisite nitrogen vacancy defect that is present in single and multi-layer hexagonal boron nitride. Our results constitute the unprecedented potential of van der Waals crystals for nanophotonics, optoelectronics and quantum information processing.
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.
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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