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Results in Optics

Enhanced photon extraction via cone structured waveguide from nitrogen vacancy center in diamond

V. Priyadarshini, A. Dharani, Subhankar Roy, Jianping Hu, M. Ummal Momeen

Published Sep 22, 2023• 2 citations
Publisher

Abstract

We present a novel design of optical nanostructure for efficient light extraction from nitrogen vacancy (NV) center in diamond. Numerical simulations of the optimal structure exhibit significant collection efficiency along with a stable radiation profile. We achieved a photon collection efficiency of 70% even with a lower numerical aperture of 0.5. Two different approaches (simple cone and encapsulated cone) have been adopted to reach a high geometrical tolerance without affecting much to the efficiency and emission profile. Besides that, our structure adds an extra benefit in terms of emission enhancement near zero phonon line (ZPL) region of NV spectra. Overall, this cone shaped diamond structure provides a robust, highly efficient and directional emission which can be integrated with a quantum optical network for various applications.

DOI
10.1016/j.rio.2023.100535

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Nature•Oct 1, 2015•0 citations
We present a novel design of optical nanostructure for efficient light extraction from nitrogen vacancy (NV) center in diamond. Numerical simulations of the optimal structure exhibit significant collection efficiency along with a stable radiation profile. We achieved a photon collection efficiency of 70% even with a lower numerical aperture of 0.5. Two different approaches (simple cone and encapsulated cone) have been adopted to reach a high geometrical tolerance without affecting much to the efficiency and emission profile. Besides that, our structure adds an extra benefit in terms of emission enhancement near zero phonon line (ZPL) region of NV spectra. Overall, this cone shaped diamond structure provides a robust, highly efficient and directional emission which can be integrated with a quantum optical network for various applications.
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.
The negatively charged nitrogen-vacancy colour center (NV(-) center) in nanodiamond is an excellent single photon source due to its stable photon generation in ambient conditions, optically addressable nuclear spin state, high quantum yield and its availability in nanometer sized crystals. In order to make practical devices using nanodiamond, highly efficient and directional emission of single photons in well-defined modes, either collimated into free space or waveguides are essential. This is a Herculean task as the photoluminescence of the NV centers is associated with two orthogonal dipoles arranged in a plane perpendicular to the NV defect symmetry axis. Here, we report on a micro-concave waveguide antenna design, which can effectively direct single photons from any emitter into either free space or into waveguides in a narrow cone angle with more than 80% collection efficiency irrespective of the dipole orientation. The device also enhances the spontaneous emission rate which further increases the number of photons available for collection. The waveguide antenna has potential applications in quantum cryptography, quantum computation, spectroscopy and metrology.
Abstract The resonant modes associated with engineered photonic structures of different spatial‐dimension are essential to obtain bright on‐demand single photon sources for quantum technologies. Negatively‐charged nitrogen‐vacancy (NV‐) center in diamond is proposed as an excellent single‐photon source at room temperature. The possible optical readout of spin states in diamond makes it a good candidate for the spin‐photon interface. However, poor light collection, feeble zero‐phonon line, low emission rate, and broad phonon‐induced emission limit the use of NV‐ centers in quantum technologies. Here, a feasible, easy‐to‐fabricate, asymmetric Tamm structure coupled with a single NV‐ center to enhance the emission rate of zero phonon line (ZPL) with better light collection efficiency is presented. The asymmetric Tamm structure shows dual resonant mode with one of the modes coinciding with NV‐ ZPL wavelength of 640 nm. The mode quality factor ( Q ‐factor) is 140, which is greater than the Q ‐factor of conventional Tamm structure and hence, improved field intensity localization. The authors achieved four times Purcell enhancement and five times enhanced light collection efficiency at 640 nm. The proposed asymmetric Tamm structure helps to generate bright single photons using NV‐ center and improves the efficacy of the spin‐photon interface.
The nitrogen-vacancy (NV) center in diamond has an optically addressable, highly coherent spin. However, an NV center even in high quality single-crystalline material is a very poor source of single photons: extraction out of the high-index diamond is inefficient, the emission of coherent photons represents just a few per cent of the total emission, and the decay time is large. In principle, all three problems can be addressed with a resonant microcavity, which significantly boosts the emission rate of coherent photons into the cavity mode based on the Purcell effect. In practice though, it has proved difficult to implement this concept: photonic engineering hinges on nano-fabrication yet it is notoriously difficult to process diamond without degrading the NV centers. \nIn this thesis, we present a microcavity scheme which employs minimally processed diamond membranes, thereby preserving the high quality of the starting material. The miniaturized plano-concave Fabry-Perot microcavity platform features full in situ spatial and spectral tunability. We demonstrate a clear change in the lifetime for multiple individual NV centers on tuning both the cavity frequency and anti-node position. The overall Purcell factor for the zero-phonon line (ZPL) of ~30 translates to an increase in the ZPL emission probability from ~3% to ~46%. \nFurthermore, we report the creation of a low-loss, broadband optical antenna giving highly directed output from a coherent single spin in the solid state. The device, the first crystalline solid-state realization of a dielectric antenna, is engineered for individual NV electronic spins in diamond. The photonic structure preserves the high spin coherence of single-crystalline diamond (T2 ~100µs). We demonstrate a directionality of close to 10 and single photon count rates approaching one MHz. The analysis of the angular emission pattern of our device suggests that 95% of the broadband NV fluorescence is channeled into a solid angle corresponding to a numerical aperture of 0.8. \nThe abovementioned approaches feature complementary benefits. The narrowband enhancement of the ZPL emission rate provided by the microcavity benefits applications in quantum information processing relying on coherent photons. With the prospect of integrating lifetime-limited emitters and achieving a high ZPL collection efficiency our results pave the way for much enhanced spin-photon and spin-spin entanglement rates. On the other hand, by channeling the major fraction of the broadband NV fluorescence into a narrow solid angle the dielectric optical antenna facilitates efficient spin readout. Our approach enables a near-unity collection efficiency which, upon mitigation of the known photon losses, renders it a potential key technology for quantum sensing applications. \n
A central goal in quantum information science is to efficiently interface photons with single optical modes for quantum networking and distributed quantum computing. Here, we introduce and experimentally demonstrate a compact and efficient method for the low-loss coupling of a solid-state qubit, the nitrogen vacancy (NV) center in diamond, with a single-mode optical fiber. In this approach, single-mode tapered diamond waveguides containing exactly one high quality NV memory are selected and integrated on tapered silica fibers. Numerical optimization of an adiabatic coupler indicates that near-unity-efficiency photon transfer is possible between the two modes. Experimentally, we find an overall collection efficiency between 16% and 37% and estimate a single photon count rate at saturation above 700 kHz. This integrated system enables robust, alignment-free, and efficient interfacing of single-mode optical fibers with single photon emitters and quantum memories in solids.