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ACS Photonics

Bright Nitrogen-Vacancy Centers in Diamond Inverted Nanocones

Seong-Woo Jeon, Jung‐Hyun Lee, Hojoong Jung, Sang-Wook Han, Young‐Wook Cho, Yong‐Su Kim, Hyang‐Tag Lim, Yanghee Kim, Matthias Niethammer, Weon Cheol Lim, Jonghan Song, Shinobu Onoda, Takeshi Ohshima, Rolf Reuter, Andrej Denisenko, Jörg Wrachtrup, Sang‐Yun Lee

Published Sep 2, 2020• 38 citations
Publisher

Abstract

Quantum emitters with long-lived quantum memories are a promising scalable quantum system for repeater-based quantum communications, quantum sensing, and distributed quantum computing networks. Although color centers in solids have been successful, further improvements in the efficiency of optical control and detection and scalability are necessary for practical uses. Here, we demonstrate that single nitrogen-vacancy centers can be efficiently coupled in diamond inverted nanocones that can be fabricated directly on the high-quality CVD diamond surface by the all-direction diagonal dry etching using a solid cone-shaped Faraday cage. Since the inverted cone shape allows efficient photon collection thanks to the single-directional guiding of photons, we report 20-fold enhancement in the photon collection efficiency from a single emitter while preserving a long electron spin coherence time. Furthermore, we show that an inverted nanocone can be picked and placed on the target position with desired orientation by using conventional microprobe tips. The demonstrated structure can also be applied to similar emitters in other solids; thus, it can be used for finding new possibilities for scalable photonic quantum devices.

DOI
10.1021/acsphotonics.0c00813

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Quantum emitters with long-lived quantum memories are a promising scalable quantum system for repeater-based quantum communications, quantum sensing, and distributed quantum computing networks. Although color centers in solids have been successful, further improvements in the efficiency of optical control and detection and scalability are necessary for practical uses. Here, we demonstrate that single nitrogen-vacancy centers can be efficiently coupled in diamond inverted nanocones that can be fabricated directly on the high-quality CVD diamond surface by the all-direction diagonal dry etching using a solid cone-shaped Faraday cage. Since the inverted cone shape allows efficient photon collection thanks to the single-directional guiding of photons, we report 20-fold enhancement in the photon collection efficiency from a single emitter while preserving a long electron spin coherence time. Furthermore, we show that an inverted nanocone can be picked and placed on the target position with desired orientation by using conventional microprobe tips. The demonstrated structure can also be applied to similar emitters in other solids; thus, it can be used for finding new possibilities for scalable photonic quantum devices.
Abstract Nanophotonic devices in color center-containing hosts provide efficient readout, control, and entanglement of the embedded emitters. Yet control over color center formation – in number, position, and coherence – in nanophotonic devices remains a challenge to scalability. Here, we report a controlled creation of highly coherent diamond nitrogen-vacancy (NV) centers with nanoscale three-dimensional localization in prefabricated nanostructures with high yield. Combining nitrogen δ -doping during chemical vapor deposition diamond growth and localized electron irradiation, we form shallow NVs registered to the center of diamond nanopillars with wide tunability over NV number. We report a positioning precision of ~ 4 nm in depth and 46(1) nm laterally in 280 nm-diameter pillars (102(2) nm in bulk diamond). We reliably form single NV centers with long spin coherence times (average T2Hahn=98 μs{T}_{2}^{Hahn}=98\, \mu {{{\rm{s}}}}T2Hahn​=98μs T 2 H a h n = 98 μ s ) and higher average photoluminescence compared to NV centers randomly positioned in pillars. Our method can improve the performance of various NV-based devices. In the realm of magnetic sensing, we achieve a 3 × improved yield of NV centers with single electron-spin sensitivity over conventional implantation-based methods. Our high-yield defect creation method will enable scalable production of solid-state defect sensors and processors.
In this work we aim to exploit one of the most studied defect color centers in diamond , the negatively charged nitrogen vacancy (NV -) color center, a three level system which emits a single photon at a wavelength of 637nm providing a possible deterministic single photon emitter very useful for quantum computing applications.Moreover the possibility of placing aNV -in a photonic crystal cavity will enhance the coupling between photons and NV -center.This could also allow us to address the ground state of the NV -center, whose spin, could be used as qubit.It is also remarkable to notice that for quantum computing purposes it is very useful to increase the light collection from the NV -centers, and in order to do that we performed a study of another structure, the solid immersion lens, which consists of an hemisphere whose center is at the position of an emitter, in this case the NV -center, increasing the collection of the light from it.In order to create these structures we used a method called focused ion beam which allowed us to etch directly into the diamond many different kinds of structures.In order to allow an interaction between these structures and the NV -centers we need to have a method to locate the NV -center precisely under the etched structures.We developed a new technique (Marseglia et al. (2011)) where we show how to mark a single NV -center and how to etch a desired structure over it on demand.This technique gave very good results allowing us to etch a solid immersion lens onto a NV -previously located and characterized, increasing the light collection from the NV -of a factor of 8×.
The long-lived electronic spin of the nitrogen-vacancy (NV) center in diamonds is a promising quantum sensor for detecting nanoscopic magnetic and electric fields in various environments. However, the poor signal-to-noise ratio (SNR) of prevalent optical spin-readout techniques presents a critical challenge in improving measurement sensitivity. Here, we address this limitation by coupling individual NVs to optimized diamond nanopillars, thereby enhancing the collection efficiency of fluorescence. Guided by near-field optical simulations, we predict improved performance for tall (≥5 μm) pillars with tapered sidewalls. This is subsequently verified by fabricating and characterizing a representative set of structures using a newly developed nanofabrication process. We observe increased SNR for optimized devices, owing to improved emission collimation and directionality. Promisingly, these devices are compatible with low-numerical-aperture collection optics and a reduced tip radius, reducing experimental overhead and facilitating improved spatial resolution for scanning applications.
We demonstrate the coupling of single color centers in diamond to plasmonic and dielectric photonic structures to realize novel nanophotonic devices. Nanometer spatial control in the creation of single color centers in diamond is achieved by implantation of nitrogen atoms through high-aspect-ratio channels in a mica mask. Enhanced broadband single-photon emission is demonstrated by coupling nitrogen-vacancy centers to plasmonic resonators, such as metallic nanoantennas. Improved photon-collection efficiency and directed emission is demonstrated by solid immersion lenses and micropillar cavities. Thereafter, the coupling of diamond nanocrystals to the guided modes of micropillar resonators is discussed along with experimental results. Finally, we present a gas-phase-doping approach to incorporate color centers based on nickel and tungsten, in situ into diamond using microwave-plasma-enhanced chemical vapor deposition. The fabrication of silicon-vacancy centers in nanodiamonds by microwave-plasma-enhanced chemical vapor deposition is discussed in addition.
Nitrogen-Vacancy (NV) centers in diamond are promising solid-state quantum emitters that can be utilized for photonic quantum applications. Various diamond nanophotonic devices have been fabricated for efficient extraction of single photons emitted from NV centers to a single guided mode. However, for constructing scalable quantum networks, further efficient coupling of single photons to a guided mode of a single-mode fiber (SMF) is indispensable and a difficult challenge. Here, we propose a novel efficient hybrid system between an optical nanofiber and a cylindrical-structured diamond nanowire. The maximum coupling efficiency as high as 75% for the sum of both fiber ends is obtained by numerical simulations. The proposed hybrid system will provide a simple and efficient interface between solid-state quantum emitters and a SMF suitable for constructing scalable quantum networks.
As the field of solid-state quantum engineering matures, it is increasingly necessary to produce quantum emitters with narrow optical transitions and long spin coherence times aligned to nanophotonic structures [1]. The nitrogen-vacancy (NV) defect center in diamond is a well-suited candidate owing to a spin ground state with a long coherence time [2], nearby nuclear spins for quantum memories [3], and spin-selective optical transitions allowing for efficient optical spin initialization and readout [4].