In this talk, our recent activities for nanofiber-integrated single light emitters for photonic quantum network. First, we report the coupling of various single light emitters, including diamond nanocrystals with color centers and hexagonal Boron Nitride flakes, to ultra-thin tapered optical fibers (nano optical fiber) with a diameter as small as 300 nm, keeping the transmittance of the fiber more than 90%. Second, for further improvement of the coupling efficiency, we introduce our development of nanofiber Bragg cavity (NFBC) with the mode volume of under 1 mu m^3 and repeatable tuning capability over more than 20 nm at visible wavelengths. The improvement of Q factor using He-ion beam milling will also be reported.
In this talk, our recent activities for nanofiber-integrated single light emitters for photonic quantum network. First, we report the coupling of various single light emitters, including diamond nanocrystals with color centers and hexagonal Boron Nitride flakes, to ultra-thin tapered optical fibers (nano optical fiber) with a diameter as small as 300 nm, keeping the transmittance of the fiber more than 90%. Second, for further improvement of the coupling efficiency, we introduce our development of nanofiber Bragg cavity (NFBC) with the mode volume of under 1 mu m^3 and repeatable tuning capability over more than 20 nm at visible wavelengths. The improvement of Q factor using He-ion beam milling will also be reported.
We analyze the coupling efficiency of a single dipole with a nanofiber Bragg cavity (NFBC) for single photon sources. Conventionally, NFBC diameters are set at approximately half of the emission wavelength to maximize coupling efficiency, but these thin structures are fragile at low temperatures. By employing three-dimensional finite difference time domain simulations, we investigate NFBCs with diameters ranging from 450 to 600 nm, which offer more mechanical robustness. Our results show that NFBCs with diameters of 450 and 500 nm achieve coupling efficiencies exceeding 80%. This study paves the way for practical single-photon sources with enhanced mechanical stability, which is crucial for applications in quantum networks and quantum computing.
The development of integrated quantum technologies relies on efficient single-photon sources and deterministic quantum operations. Solid-state quantum emitters coupled to nanophotonic structures present a promising solution. This work investigates color centers in nanodiamonds,particularly Germanium Vacancy (GeV) [1], Silicon Vacancy (SiV), and Magnesium Vacancy (MgV) centers, a novel, understudied emitter [2], at both room and cryogenic temperatures. These nanodiamonds are chosen for their stability and superior coherence properties at cryogenic conditions. To collect their emission we have successfully deposited a single GeV- nanodiamond on tapered optical nanofibers by gently contacting a diluted droplet to the nanofiber [3], demonstrating an average coupling of 15% into a conventional optical fiber through the confined evanescent field of the nanofiber mode and single photon emission. Building on this achievement, we aim to study the system at cryogenic temperatures, which should enable the demonstration of efficient and indistinguishable single photons coupling to conventional optical fibers.Current collection efficiencies are intrinsically limited to 30% with the nanofiber[4], and improving light-matter coupling efficiency remains a key goal for high-performance single-photon sources and more advanced applications.To achieve this, we are investigating a newly developed technique [5]: the deterministic fabrication of dielectric and plasmonic nanostructures directly on the nanofiber surface using an “electron beam induced deposition” (EBID). The precision and versatility of this technique openthe way to different applications: Purcell enhancement of the quantum emitter emission using metallic nanoantennas and efficient light-matter coupling using dielectric structures. Our first calculation shown that optimizing the composition, geometry, and placement of these nanostructures a simple pattern of carbon pillars around the emitter should increase coupling efficiency up to 69% while maintaining high transmission in the nanofiber. We also demonstratethe fabrication of those nanostructures on top of the nanofiber.This work advances integrated nanophotonic devices for single-photon sources.[1] M. Nahra et al.,Single germanium vacancy centers in nanodia-monds with bulk-like spectral stability, AVS Quantum Science3(1), (2021).[2] E. Corte et al, Magnesium-Vacancy Optical Centers in Diamond, ACS Photonics, 10(1), p101-110, (2023)[3] Pierini et al. Highly Photostable Perovskite Nanocubes : TowardIntegrated Single Photon Sources Based on Tapered Nanofibers.ACS Photonics, 7(8), p.2265-2272, (2020).[4] Fujiwara et al., Highly efficient coupling of photons from na-noemitters into single-mode optical fibers, Nano Letters, 11(10),4362–4365, (2011).[5] A.Balena et al, Deterministic Bottom-Up Fabrication of Plasmonic Nanostructures on OpticalNanofibers via Blurred Electron Beam Deposition (soon to be published in Advance Material).
Funnelling the light emitted from quantum emitters like atoms, molecules, or defect centers into the guided mode of a single mode optical fiber is highly important for scaling up quantum optics experiments, since it provides the possibility to interconnect experiments at different locations and ensures high mode overlap of photons from different sources. Here, we present a photonic nanocavity on a tapered optical fiber. The cavities are formed by two Bragg mirrors fabricated by an ion beam [1]. Characterization in terms of transmission, reflection, and polarization are performed and compared with numerical simulations [2]. The quality factors of the fabricated devices can reach values over 300 while the mode volume is smaller than the cubic wavelength. Simulations indicate that a Purcell enhancement of 19.1 with 82 % coupling efficiency can be reached using this cavities. A comparison of cavities fabricated using a gallium beam is compared with cavities made using a helium beam giving insights about implantation of gallium in the ion beam milling fabrication of resonators. Using the knowledge from experiment and simulation, new designs for nanofiber Bragg grating cavities are developed and tested. [1] A W Schell et al. Sci. Rep. 5, 9619 (2015) [2] H Takashima et al. Opt. Express 24, 15050-15058 (2016)
Efficient coupling of photons emitted from single light emitters into the single guided mode of an optical fiber is important to realize photonic quantum network devices [1], such as single photon sources [2] and quantum phase gates [3]. For this purpose, we have developed nanofiber Bragg cavities (NFBCs) and observed the enhanced photon emission from the single light emitter [4]. Here, we report the development of the NFBC with the Q-factor of 1560, which is about 5 times larger than our previous NFBC fabricated by a gallium focused ion beam (FIB) milling system [4]. According to numerical simulation, the NFBC with such high-ß factor can be realized Purcell factor of about 18 and the coupling efficiency of about 80 %.
Abstract Recent advances in the coherent control of single quanta of light, photons , is a topic of prime interest, and is discussed under the banner of quantum photonics . In the last decade, the subwavelength diameter waist of a tapered optical fiber, referred to as an optical nanofiber , has opened promising new avenues in the field of quantum optics, paving the way toward a versatile platform for quantum photonics applications. The key feature of the technique is that the optical field can be tightly confined in the transverse direction while propagating over long distances as a guided mode and enabling strong interaction with the surrounding medium in the evanescent region. This feature has led to surprising possibilities to manipulate single atoms and fiber-guided photons, e.g. the efficient channeling of emission from single atoms and solid-state quantum emitters into the fiber-guided modes, high optical depth with a few atoms around the nanofiber, trapping atoms around a nanofiber, and atomic memories for fiber-guided photons. Furthermore, implementing a moderate longitudinal confinement in nanofiber cavities has enabled the strong coupling regime of cavity quantum electrodynamics to be reached, and the long-range dipole–dipole interaction between quantum emitters mediated by the nanofiber offers a platform for quantum nonlinear optics with an ensemble of atoms. In addition, the presence of a longitudinal component of the guided field has led to unique capabilities for chiral light–matter interactions on nanofibers. In this article, we review the key developments of the nanofiber technology toward a vision for quantum photonics on an all-fiber interface.