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Evaluation of spectral properties and coupling efficiency using diamond nanobeams and tapered fibers

K. Aoyama, Y. Sekiguchi, H. Kurokawa, M. Kamata, M. Kunii, S. Ishida, H. Matsukiyo, Natthajuks Pholsen, Masao Nishioka, S. Ji, H. Otsuki, T. Ishihara, Kimura Kosuke, Takenaka Kouta, Onoda Shinobu, T. Baba, S. Iwamoto, H. Kosaka

Published Aug 20, 2026• 0 citations
OpenAlex

Abstract

We demonstrate an optical interface between diamond nanobeams and tapered fibers via adiabatic coupling for quantum networks. We estimated up to 56% coupling efficiency by FDTD and experimentally achieved 13%. This work guides the development of robust optical coupling packages.

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•Jan 1, 2015•0 citations
Efficient and stable interfaces between quantum devices and optical fibers are a key requirement for realizing large-scale quantum networks and distributed quantum computing. Adiabatic coupling between a diamond waveguide and a tapered fiber provides a promising route to broadband, efficient, and robust optical coupling [*]. In this work, we present the design, fabrication, and characterization of such interface. First, we performed FDTD simulations to optimize the diamond nanobeam geometry. These simulations predict a maximum coupling efficiency of 98% with an optimized design. Next, tapered optical fibers with angles <3° and tips <150 nm were fabricated using an optimized hydrofluoric acid etching process. Finally, we experimentally evaluated the coupling efficiency by measuring photoluminescence from nitrogen-vacancy centers in a diamond nanobeam through the fiber, yielding an efficiency of 14%. These results establish a clear design path for a practical interface. The gap between simulation and experiment highlights the need to improve physical contact and nanobeam fabrication. Future work will target these optimizations to realize a more efficient and robust packaged device, a critical component for quantum networks.
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.
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. A compact way to efficiently couple a solid-state qubit, the nitrogen vacancy center in diamond, with a single-mode optical fiber is shown. The ability to efficiently couple stationary quantum memories to a single spatial mode in a silica fiber is highly desired for various applications in quantum information processing. Now, Rishi Patel and co-workers, working in the group of Dirk Englund at the Massachusetts Institute of Technology have proposed and experimentally demonstrated an approach involving adiabatic power transfer between a tapered silica fiber and a single-mode micro-waveguide made from high-quality diamond. This integrated diamond–silica waveguide system enables optical collection from nitrogen vacancy centers with overall efficiencies in the range 16%–37%—a roughly four-fold improvement over previous approaches that employed diamond point emitters rather than waveguiding structures. Numerical optimization analysis suggests that near-unity efficiencies are theoretically feasible.
A diamond nano-crystal hosting a single nitrogen vacancy (NV) center is optically selected with a confocal scanning microscope and positioned deterministically onto the subwavelength-diameter waist of a tapered optical fiber (TOF) with the help of an atomic force microscope. Based on this nano-manipulation technique, we experimentally demonstrate the evanescent coupling of single fluorescence photons emitted by a single NV-center to the guided mode of the TOF. By comparing photon count rates of the fiber-guided and the free-space modes and with the help of numerical finite-difference time domain simulations, we determine a lower and upper bound for the coupling efficiency of (9.5 ± 0.6)% and (10.4 ± 0.7)%, respectively. Our results are a promising starting point for future integration of single photon sources into photonic quantum networks and applications in quantum information science.
Tapered optical fibers are promising one-dimensional nanophotonic waveguides that can provide efficient coupling between their fundamental mode and quantum nanoemitters placed inside them. Here, we present numerical studies on the coupling of single nitrogen-vacancy (NV) centers (single point dipoles) in nanodiamonds with tapered fibers. Our results lead to two important conclusions: (1) A maximum coupling efficiency of 53.4% can be realized for the two fiber ends when the NV bare dipole is located at the center of the tapered fiber. (2) NV centers even in 100-nm-sized nanodiamonds where bulk-like optical properties were reported show a coupling efficiency of 22% at the taper surface, with the coupling efficiency monotonically decreasing as the nanodiamond size increases. These results will be helpful in guiding the development of hybrid quantum devices for applications in quantum information science.