The nitrogen vacancy (NV) center is the most widely studied single optical defect in diamond with great potential for applications in quantum technologies. Development of practical single-photon devices requires an understanding of the emission under a range of conditions and environments. In this work, we study the properties of a single NV center in nanodiamonds embedded in an air-like silica aerogel environment which provides a new domain for probing the emission behavior of NV centers in nanoscale environments. In this arrangement, the emission rate is governed primarily by the diamond crystal lattice with negligible contribution from the surrounding environment. This is in contrast to the conventional approach of studying nanodiamonds on a glass coverslip. We observe an increase in the mean lifetime due to the absence of a dielectric interface near the emitting dipoles and a distribution arising from the irregularities in the nanodiamond geometry. Our approach results in the estimation of the mean quantum efficiency (~0.7) of the nanodiamond NV emitters.
Single-photon sources and their optical spin readout are at the core of applications in quantum communication, quantum computation, and quantum sensing. Their integration in photonic structures such as photonic crystals, microdisks, microring resonators, and nanopillars is essential for their deployment in quantum technologies. While there are currently only two material platforms (diamond and silicon carbide) with proven single-photon emission from the visible to infrared, a quantum spin–photon interface, and ancilla qubits, it is expected that other material platforms could emerge with similar characteristics in the near future. These two materials also naturally lead to monolithic integrated photonics as both are good photonic materials. While so far the verification of single-photon sources was based on discovery, assignment and then assessment and control of their quantum properties for applications, a better approach could be to identify applications and then search for the material that could address the requirements of the application in terms of quantum properties of the defects. This approach is quite difficult as it is based mostly on the reliability of modeling and predicting of color center properties in various materials, and their experimental verification is challenging. In this paper, we review some recent advances in an emerging material, low-dimensional (2D, 1D, 0D) hexagonal boron nitride (h-BN), which could lead to establishing such a platform. We highlight the recent achievements of the specific material for the expected applications in quantum technologies, indicating complementary outstanding properties compared to the other 3D bulk materials.
Bright, room‐temperature stable, on‐demand, and highly directional light sources are essential for quantum optical technologies. A design methodology to enhance the emission and collection efficiencies for given collection optics is proposed and demonstrated. Hyperbolic metamaterials (HMMs) offer manipulation of local density of states to improve the emission as well as coupling of emission to high‐K modes. However, metallic losses limit the efficiencies achieved. The HMM structure designed for large, broadband Purcell enhancement with limited metallic losses as well as HMM and antenna design to optimize the collection efficiency is presented. 200 times emission enhancement is reported from CdSeS/ZnS core/shell alloyed quantum dots embedded in a planar HMM structure with cylindrical silver (Ag) patch antenna on the top. 40% collection efficiency is demonstrated for a lens with a numerical aperture of 0.9 and the emission enhancement is about an order of magnitude higher than the previous reports.
We report the enhancement of the optical emission between 850 and 1400 nm of an ensemble of silicon mono-vacancies (VSi), silicon and carbon divacancies (VCVSi), and nitrogen vacancies (NCVSi) in an n-type 4H-SiC array of micropillars. The micropillars have a length of ca. 4.5 μm and a diameter of ca. 740 nm, and were implanted with H+ ions to produce an ensemble of color centers at a depth of approximately 2 μm. The samples were in part annealed at different temperatures (750 and 900 °C) to selectively produce distinct color centers. For all these color centers we saw an enhancement of the photostable fluorescence emission of at least a factor of 6 using micro-photoluminescence systems. Using custom confocal microscopy setups, we characterized the emission of VSi measuring an enhancement by up to a factor of 20, and of NCVSi with an enhancement up to a factor of 7. The experimental results are supported by finite element method simulations. Our study provides the pathway for device design and fabrication with an integrated ultra-bright ensemble of VSi and NCVSi for in vivo imaging and sensing in the infrared.
We model the broadband enhancement of single-photon emission from color centres in silicon carbide nanocrystals coupled to a planar hyperbolic metamaterial (HMM) resonator.The design is based on positioning the single photon emitters within the HMM resonator, made of a dielectric index-matched with silicon-carbide material. The broadband response results from the successive resonance peaks of the lossy Fabry-Perot structure modes arising within the high-index HMM cavity. To capture this broadband enhancement in the single photon emitter's spontaneous emission, we placed a simple gold based cylindrical antenna on top of the HMM resonator. We analyzed the performance of this HMM coupled antenna structure in terms of the Purcell enhancement, quantum efficiency, collection efficiency and overall collected photon rate. For perpendicular dipole orientation relative to the interface, the HMM coupled antenna resonator leads to a significantly large spontaneous emission enhancement with Purcell factor of the order of 250 along with a very high average total collected photon rate (CPR) of about 30 over a broad emission spectrum (700 nm -1000 nm). The peak CPR increases to about 80 at 900 nm, corresponding to the emission of silicon-carbide quantum emitters. This is a state-of-the art improvement considering the previous computational designs have reported a maximum average CPR of 25 across the nitrogen-vacancy centre emission spectrum, 600 nm to 800 nm with the highest value being about 40 at 650 nm.
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