Extracting photons from defect centers is challenging due to the high refractive index of typical substrates. For nitrogen-vacancy centers in diamond, reaching saturation count rates above 2.5 × 10 5 counts/s so far requires nanofabricated optics, such as diamond waveguides or solid immersion lenses. Here, we present an experimental and theoretical study of defect center emission at unmodified planar dielectric surfaces by quantitative back-focal-plane imaging and analytical modeling. Our results indicate that photon count rates approaching those of nanofabricated optics can also be achieved by oil-immersion optics. This is due to a dielectric antenna effect, which directs the majority of the emission into the substrate within a narrow angle window suitable for back-side collection. By quantification of the collection efficiency of back-side detection, our work also enables a novel measurement method for the quantum efficiency of shallow defect centers. Its result challenges established values. Possible reasons for the discrepancy are discussed.
Extracting photons from defect centers is challenging due to the high refractive index of typical substrates. For nitrogen-vacancy centers in diamond, reaching saturation count rates above 2.5 × 10 5 counts/s so far requires nanofabricated optics, such as diamond waveguides or solid immersion lenses. Here, we present an experimental and theoretical study of defect center emission at unmodified planar dielectric surfaces by quantitative back-focal-plane imaging and analytical modeling. Our results indicate that photon count rates approaching those of nanofabricated optics can also be achieved by oil-immersion optics. This is due to a dielectric antenna effect, which directs the majority of the emission into the substrate within a narrow angle window suitable for back-side collection. By quantification of the collection efficiency of back-side detection, our work also enables a novel measurement method for the quantum efficiency of shallow defect centers. Its result challenges established values. Possible reasons for the discrepancy are discussed.
The efficiency of photon collection from optically active defect centers in bulk diamond is greatly reduced by refraction at the diamond-air interface. We report on the fabrication and measurement of a geometrical solution to the problem; integrated solid immersion lenses (SILs) etched directly into the surface of diamond. An increase of a factor of 10 was observed in the saturated count-rate from a single negatively charged nitrogen-vacancy (NV−) within a 5 μm diameter SIL compared with NV−’s under a planar surface in the same crystal. Such a system is potentially scalable and easily adaptable to other defect centers in bulk diamond.
An efficient atom–photon interface is a key requirement for the integration of solid-state emitters, such as color centers in diamond, into quantum technology applications. As other solid-state emitters, however, their emission into free space is severely limited due to the high refractive index of the bulk host crystal. In this work, we present a planar optical antenna based on two silver mirrors coated on a thin single crystal diamond membrane, forming a planar Fabry–Pérot cavity that improves the photon extraction from single tin vacancy (SnV) centers and their coupling to an excitation laser. Upon numerical optimization of the structure, we find theoretical enhancements in the collectible photon rate by a factor of 60 as compared to the bulk case. As a proof-of-principle demonstration, we fabricate single crystal diamond membranes with sub-μm thickness and create SnV centers by ion implantation. Employing off-resonant excitation, we show a sixfold enhancement of the collectible photon rate, yielding up to half a million photons per second from a single SnV center. At the same time, we observe a significant reduction of the required excitation power in accordance with theory, demonstrating the functionality of the cavity as an optical antenna. Due to its planar design, the antenna simultaneously provides similar enhancements for a large number of emitters inside the membrane. Furthermore, the monolithic structure provides high mechanical stability and straightforwardly enables operation under cryogenic conditions as required in most spin–photon interface implementations.
Enhancing the collection efficiency of single emitters via dielectric antennas is a common approach in research dealing with solid-state quantum light sources. Current design concepts often suffer from a large footprint, quenching or a complex fabrication process. Here we report on another design where the Kerker effect is used to collimate emission from a nitrogen vacancy (NV) center. The structure discussed here is an easy to fabricate cylindrical protrusion made from diamond on top of a diamond substrate with NVs incorporated into its center. We optimize the structure with respect to application in quantum information processing and quantum sensing and find an up to 15 times higher photon extraction.
ABSTRACT The negatively charged nitrogen‐vacancy (NV) center in diamond is a leading solid‐state quantum emitter, offering spin‐photon interfaces over a wide temperature range with applications from electromagnetic sensing to bioimaging. While NV centers in bulk diamond are well understood, embedding them in nanodiamond (ND) introduces complexities from size, NV location, and NV polarizations. NVs in ND show altered fluorescence properties, including longer lifetimes, lower quantum efficiency, and higher sensitivity to dielectric surroundings, which arise from radiative suppression, surface‐induced non‐radiative decay, and escape inefficiency at the diamond‐background interface. Prior models typically addressed isolated aspects, such as dielectric contrast or surface quenching, without integrating full quantum‐optical NV behavior with classical electrodynamics. We present a hybrid framework coupling rigorous electromagnetic simulations with a quantum‐optical NV model including phonon sideband dynamics. NV emission is found to depend strongly on ND size, NV position, and surrounding refractive index. Our results explain observations such as shallow NVs in water‐coated ND appearing brighter than deeper ones in air. This integrated model provides a unified framework for realistic NV in ND emission scenarios and informs the design of efficient NV‐based sensors and quantum devices, advancing understanding of quantum emitter photophysics in nanoscale crystals.
We use crystalline silicon (Si) antennas to efficiently extract broadband single-photon fluorescence from shallow nitrogen-vacancy (NV) centers in diamond into free space. Our design features relatively easy-to-pattern high-index Si resonators on the diamond surface to boost photon extraction by overcoming total internal reflection and Fresnel reflection at the diamond-air interface and providing modest Purcell enhancement, without etching or otherwise damaging the diamond surface. In simulations, ∼17 times more single photons are collected from a single NV center compared to the case without the antenna; in experiments, we observe an enhancement of ∼9 times, limited by spatial alignment between the NV and the antenna. Our approach can be readily applied to other color centers in diamond, and more generally to the extraction of light from quantum emitters in wide-bandgap materials.
Abstract Optically active defects in diamond are widely used as bright single‐photon sources for quantum sensing, computing, and communication. For many applications, it is useful to place the emitter close to the diamond surface, where the radiative properties of the emitter are strongly modified by its dielectric environment. It is well‐known that the radiative power from an electric dipole decreases as the emitter approaches an interface with a lower‐index dielectric, leading to an increase in the radiative lifetime. For emitters in crystalline solids, modeling of this effect needs to take into account the crystal orientation and direction of the surface cut, which can greatly impact the emission characteristics. In this paper, a framework for analyzing the emission rates of shallow (<100 nm) defects is provided, in which optical transitions are derived from electric dipoles in a plane perpendicular to their spin axis. The calculations for the depth‐dependent radiative lifetime for color centers in (100)‐, (110)‐, and (111)‐cut diamond are presented, which can be extended to other vacancy defects in diamond.