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).
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).
The interaction of photons with individual quantum systems is a very fundamental process in physics. Thereby, the emission rate as well as the angular emission pattern of a quantum emitter are not only a function of intrinsic properties of the emitter itself, but are also strongly modified by its surrounding. For instance, by restricting the optical modes which are allowed at the position of the dipole, the emission rate can be strongly modified and the emitted photons can be directed into specific optical modes. This effect can be demonstrated by the interaction of a single optically active quantum emitter with the strongly confined optical mode of a single-mode dielectric waveguide. Efficient coupling of the emitter to the dielectric structure can be achieved by placing the quantum emitter inside the evanescent field of the guided mode. This evanescent field coupling mechanism is discussed and demonstrated experimentally. A single nitrogen-vacancy center (NV-center), hosted in a nanodiamond is deterministically coupled to a tapered optical fiber (TOF) via the evanescent field of its guided mode (coupling efficiencies exceeding 30% are predicted). By employing an AFM-based nanomanipulation technique, the diamond nanocrystal is placed on the nanofiber waist of the TOF. Beforehand, the diamond nanocrystal has been characterized to guarantee that it hosts only one fluorescing NV-center. While the diamond nanocrystal is optically exited, single photon fluorescence of the NV-center is detected at both outputs of the tapered optical fiber. This verifies the evanescent coupling of the emitter to the guided mode. In order to quantify the coupling, the comparison of the emission rate into free space with the rate into the fiber yields that 10.0(5) of the emitted photons are coupled into the tapered optical fiber. In the determination of this value, the orientation of the emitting dipoles and the emission pattern, which are modified by the TOF, have been considered. The NV-center features a broad emission spectrum which can be used to investigate the wavelength-dependence of the coupling. Comparing the spectra of the emission into the fiber mode with the emission into free space modes roughly resembles the expected wavelength dependency of the coupling efficiency. The evanescent coupling and the deterministic positioning of preselected fluorescing diamond nanocrystals, which has been demonstrated with the TOF, can be applied to other waveguide structures as well. Dielectric single-mode waveguides made of Ta2O5 on a SiO2 substrate promise similar coupling efficiencies to tapered optical fibers (above 30%). With the design of the on-chip wave-guiding structure being flexible, the combination with other optical on-chip elements is feasible, rendering it a promising platform for on-chip photonic experiments. Test structures of this waveguide design are realized using lithographic processes and are characterized. These waveguides are equipped with inverted taper structures to allow efficient off-chip coupling with butt-coupling to standard single-mode fibers. The evanescent coupling of a single quantum emitter to a singe optical mode can be used to efficiently collect emission of the quantum emitter. This can help building a compact single photon source and is beneficial for the optical read-out of the quantum emitter's internal degree of freedom, which can be either used as probe (sensing) or as information-storage. Utilizing the high coupling efficiency, for instance, the non-linearities of the quantum system can be exploited to build a single photon transistor. The evanescent coupling is very broadband (about hundred nanometers), allowing to efficiently collect emission from broadband emitters like the NV-center, but it can also be used for multi-wavelength manipulation schemes.
NV center in diamond is attracting a lot of attention in quantum information processing community [1]. Been spin system in clean and well-controlled environment of diamond it shows outstanding performance as quantum memory even at room temperature, spin control with single shot optical readout and possibility to build up quantum registers even on single NV center. Moreover, NV centers could be used as high-resolution sensitive elements of detectors of magnetic or electric field, temperature, tension, force or rotation. For all of these applications collection of the light emitted by NV center is crucial point. There were number of approaches suggested to address this issue, proposing use of surface plasmoms [2], manufacturing structures in diamond [3] etc. One of the key feature of any practically important interface is compatibility with the fiber technology. Several groups attacking this problem using various approaches. One of them is placing of nanodiamonds in the holes of photonic crystal fiber [4], another is utilization of AFM to pick and place nanodiamond on the tapered fiber[5]. We have developed a novel technique of placing a nanodiamond with single NV center on the tapered fiber by controlled transfer of a nanodiamond from one “donor” tapered fiber to the “target” clean tapered fiber. We verify our ability to transfer only single color centers by means of measurement of second order correlation function. With this technique, we were able to double collection efficiency of confocal microscope. The majority of the factors limiting the collection of photons via optical fiber are technical and may be removed allowing order of magnitude improved in collection. We also discuss number of extensions of this technique to all fiber excitation and integration with nanostructures. References: [1] Marcus W. Doherty, Neil B. Manson, Paul Delaney, Fedor Jelezko, Jörg Wrachtrup, Lloyd C.L. Hollenberg , " The nitrogen-vacancy colour centre in diamond," Physics Reports, vol. 528, no. 1, p. 1–45, 2013. [2] A.V. Akimov, A. Mukherjee, C.L. Yu, D.E. Chang, A.S. Zibrov, P.R. Hemmer, H. Park and M.D. Lukin, "Generation of single optical plasmons in metallic nanowires coupled to quantum dots," Nature, vol. 450, p. 402–406, 2007. [3] Michael J. Burek , Yiwen Chu, Madelaine S.Z. Liddy, Parth Patel, Jake Rochman , Srujan Meesala, Wooyoung Hong, Qimin Quan, Mikhail D. Lukin and Marko Loncar High quality-factor optical nanocavities in bulk single-crystal diamond, Nature communications 6718 (2014) [4] Tim Schroder, Andreas W. Schell, Gunter Kewes, Thomas Aichele, and Oliver Benson Fiber-Integrated Diamond-Based Single Photon Source, Nano Lett. 2011, 11, 198-202 [5]Lars Liebermeister, et. al. “Tapered fiber coupling of single photons emitted by a deterministically positioned single nitrogen vacancy center”, Appl. Phys. Lett. 104, 031101 (2014)
We present a fiber-coupled diamond-based single photon system. Single nanodiamonds containing nitrogen vacancy defect centers are deposited on a tapered fiber of 273 nanometer in diameter providing a record-high number of 689,000 single photons per second from a defect center in a single-mode fiber. The system can be cooled to cryogenic temperatures and coupled evanescently to other nanophotonic structures, such as microresonators. The system is suitable for integrated quantum transmission experiments, two-photon interference, quantum-random-number generation and nano-magnetometry.
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.
Further miniaturization of funcionalized quantum optical systems down to nm-dimensions and their integration into fibre optical networks is a major challange for future implementations of quantum information, quantum communication and quantum processing applications. Furthermore, scalability, long-term stability and room- as well as liquid helium temperature operation are benchmarking properties of such systems. In this paper, we present the realizations of fiber-coupled diamond-based single photon systems. First, an alignment free, μm-scale single photon source consisting of a single nitrogen vacancy center facet coupled to an optical fiber operating at room temperature is presented. Near-field coupling of the single nitrogen vacancy center is realized by placing a pre-selected nanodiamond directly on the fiber facet in a bottom-up approach. Its photon collection efficiency is comparable to a far-field collection via an air objective with a numerical aperture of 0.82. As the system can be simultaneously excited and its photons be recollected through the fiber, it can be used as a fiber-connected single quantum sensor that allows optical near-field probing on the quantum level. Secondly single nanodiamonds that contain nitrogen vacancy defect centers, are near-field coupled to a tapered fiber of 300 nanometer in diameter. This system provides a record-high number of 97 kcps single photons from a single defect center into a single mode optical fiber. The entire system can be cooled to liquid Helium temperatures and reheated without breaking. Furthermore, the system can be evanescently coupled to various nanophotonic structures, e.g. microresonators. The system can also be applied for integrated quantum transmission experiments and the realization of two-photon interference. It can be used as a quantum-randomnumber generator as well as a probe for nano-magnetometry.
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.