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arXiv:1903.05446 · Nanophotonics

Ultrabright single‐photon emission from germanium‐vacancy zero‐phonon lines: deterministic emitter‐waveguide interfacing at plasmonic hot spots

Hamidreza Siampour, Ou Wang, Vladimir A. Zenin, Sergejs Boroviks, Petr Siyushev, Yuanqing Yang, Валерий Александрович Давыдов, L. F. Kulikova, V. Agafonov, Alexander Kubanek, N. Asger Mortensen, Fedor Jelezko, Sergey I. Bozhevolnyi

Published Feb 1, 2020• 44 citations
arXivHTMLPDF

Abstract

Abstract Striving for nanometer‐sized solid‐state single‐photon sources, we investigate atom‐like quantum emitters based on single germanium‐vacancy (GeV) centers isolated in crystalline nanodiamonds (NDs). Cryogenic characterization indicated symmetry‐protected and bright (>10 6 counts/s with off‐resonance excitation) zero‐phonon optical transitions with up to 6‐fold enhancement in energy splitting of their ground states as compared to that found for GeV centers in bulk diamonds (i.e. up to 870 GHz in highly strained NDs vs. 150 GHz in bulk). Utilizing lithographic alignment techniques, we demonstrate an integrated nanophotonic platform for deterministic interfacing plasmonic waveguides with isolated GeV centers in NDs, which enables 10‐fold enhancement of single‐photon decay rates along with the emission direction control by judiciously designing and positioning a Bragg reflector. This approach allows one to realize the unidirectional emission from single‐photon dipolar sources, thereby opening new perspectives for the realization of quantum optical integrated circuits.

DOI
10.1515/nanoph-2020-0036

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Abstract Striving for nanometer‐sized solid‐state single‐photon sources, we investigate atom‐like quantum emitters based on single germanium‐vacancy (GeV) centers isolated in crystalline nanodiamonds (NDs). Cryogenic characterization indicated symmetry‐protected and bright (>10 6 counts/s with off‐resonance excitation) zero‐phonon optical transitions with up to 6‐fold enhancement in energy splitting of their ground states as compared to that found for GeV centers in bulk diamonds (i.e. up to 870 GHz in highly strained NDs vs. 150 GHz in bulk). Utilizing lithographic alignment techniques, we demonstrate an integrated nanophotonic platform for deterministic interfacing plasmonic waveguides with isolated GeV centers in NDs, which enables 10‐fold enhancement of single‐photon decay rates along with the emission direction control by judiciously designing and positioning a Bragg reflector. This approach allows one to realize the unidirectional emission from single‐photon dipolar sources, thereby opening new perspectives for the realization of quantum optical integrated circuits.
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).
Motivated by the success of group IV color centers in nanodiamonds (NDs) for hybrid technology requiring a single photon source, the authors study single germanium-vacancy (GeV−) centers in NDs at room temperature with size ranging from 10 to 50 nm and with remarkable spectral properties. The authors characterize their zero-phonon line, study their internal population dynamics, and compare their emission properties in the framework of a three level model with intensity dependent de-shelving. Furthermore, the authors characterize their lifetime, polarization, and brightness. The authors find a maximum photon emission count rate of 1.6 MHz at saturation. The authors also report a polarization visibility of 92% from the fluorescence light, which potentially makes GeV− centers good candidates for quantum key distribution requiring polarized single photons. The authors show that GeV− centers in NDs presented in this work have a comparable spectral stability compared to their bulk counterpart, which is needed for future applications using nanodiamonds.
Abstract Diamond color centers have been widely studied in the field of quantum optics. The negatively charged silicon vacancy (SiV − ) center exhibits a narrow emission linewidth at the wavelength of 738 nm, a high Debye–Waller factor, and unique spin properties, making it a promising emitter for quantum information technologies, biological imaging, and sensing. In particular, nanodiamond (ND)‐based SiV − centers can be heterogeneously integrated with plasmonic and photonic nanostructures and serve as in vivo biomarkers and intracellular thermometers. Out of all methods to produce NDs with SiV − centers, ion implantation offers the unique potential to create controllable numbers of color centers in preselected individual NDs. However, the formation of single color centers in NDs with this technique has not been realized. We report the creation of single SiV − centers featuring stable high‐purity single‐photon emission through Si implantation into NDs with an average size of ∼20 nm. We observe room temperature emission, with zero‐phonon line wavelengths in the range of 730–800 nm and linewidths below 10 nm. Our results offer new opportunities for the controlled production of group‐IV diamond color centers with applications in quantum photonics, sensing, and biomedicine.
We demonstrate a quantum nanophotonics platform based on germanium-vacancy (GeV) color centers in fiber-coupled diamond nanophotonic waveguides. We show that GeV optical transitions have a high quantum efficiency and are nearly lifetime broadened in such nanophotonic structures. These properties yield an efficient interface between waveguide photons and a single GeV center without the use of a cavity or slow-light waveguide. As a result, a single GeV center reduces waveguide transmission by 18±1% on resonance in a single pass. We use a nanophotonic interferometer to perform homodyne detection of GeV resonance fluorescence. By probing the photon statistics of the output field, we demonstrate that the GeV-waveguide system is nonlinear at the single-photon level.
Abstract Integrated on‐demand single‐photon sources are critical for the implementation of photonic quantum information processing systems. To enable practical quantum photonic devices, the emission rates of solid‐state quantum emitters need to be substantially enhanced and the emitted signal must be directly coupled to an on‐chip circuitry. The photon emission rate speed‐up is best achieved via coupling to plasmonic antennas, while on‐chip integration can be realized by directly coupling emitters to photonic waveguides. The realization of practical devices requires that both the emission speed‐up and efficient out‐coupling are achieved in a single architecture. Here, a novel architecture is proposed that combines chip compatibility with high radiative emission rates—a quantum plasmonic launcher. The proposed launchers contain single nitrogen‐vacancy (NV) centers in nanodiamonds as quantum emitters that offer record‐high average fluorescence lifetime shortening factors of about 7000 times. Nanodiamonds with single NVs are sandwiched between two silver films that couple more than half of the emission into in‐plane propagating surface plasmon polaritons. This simple, compact, and scalable architecture represents a crucial step toward the practical realization of high‐speed on‐chip quantum networks.