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Symposium Latsis on Diamond Photonics - Physics, Technologies and Applications

Atom-like quantum emitters embedded in photonic hot spots

Hamidreza Siampour, Ou Wang, Валерий Александрович Давыдов, V. Agafonov, Fedor Jelezko, Sergey I. Bozhevolnyi

Published Jan 1, 2019• 0 citations
Publisher

Abstract

We investigate symmetry-protected quantum emitters based on single germanium vacancy (GeV) centers in nanodiamonds (NDs). Cryogenic characterization indicated bright zero-phonon lines with large splitting in their ground states. Deterministic integration of the NDs at photonic hot spots enabled to enhance the total emission decay rate by a factor of 10.

DOI
10.1364/dp.2019.56

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We investigate symmetry-protected quantum emitters based on single germanium vacancy (GeV) centers in nanodiamonds (NDs). Cryogenic characterization indicated bright zero-phonon lines with large splitting in their ground states. Deterministic integration of the NDs at photonic hot spots enabled to enhance the total emission decay rate by a factor of 10.
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.
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.
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).
Quantum photonics platforms hold considerable potential for the rapid development and deployment of quantum information and computing technologies. Color centers in diamond, such as silicon-vacancy (SiV) centers, have numerous attractive properties for such applications, including high brightness, narrow zero-phonon line (ZPL) linewidths at 737nm, and stable single-photon emission insusceptible to electric field fluctuations [1]. Color centers in photonic diamond nanostructures have been demonstrated recently [2], but their fabrication is challenging and requires sophisticated techniques and equipment.
Nanodiamonds containing single tin-vacancy (SnV) centers have the potential for integration into nanophotonic devices employed in quantum technologies such as quantum sensing, quantum information processing and quantum communication. The present study assessed single SnV centers in nanodiamonds less than 10 nm in size. Such centers were generated by implanting Sn ions into size-selected small nanodiamonds followed by high-temperature annealing. A sharp emission peak with a line width of 2.6 nm was observed at 618.7 nm, corresponding to the zero phonon line of SnV centers in bulk diamond. The Debye–Waller factor for this peak at room temperature was estimated to be 0.38 and so was slightly greater than the value for bulk diamond. A second-order correlation function yielded a g 2 (0) value of 0.04 ± 0.11, indicating single-photon emission. The successful creation of single SnV centers in nanodiamonds is a critical step toward integrating nanophotonic devices for photonic quantum technologies.
Efficient coupling between quantum emitters and optical cavities is essential for scalable quantum photonic technologies. Group-IV vacancy centers in diamond, particularly the negatively charged tin-vacancy center, have emerged as promising candidates due to their spectral stability, high Debye-Waller factor, and large orbital splitting in ground states. Here, we demonstrate controlled coupling of a single negatively charged tin-vacancy center hosted in a nanodiamond to a fully tunable Fabry-Pérot microcavity. At cryogenic temperatures, we access the weak-coupling regime and observe a transition from the bad-emitter regime to the bad-cavity regime as the optical transition of the color center narrows. At 4 K, a Purcell factor exceeding 1.7 is measured, confirming cavity-enhanced emission. The obtained results demonstrate the potential of Sn − V − centers in nanodiamonds as a coherent single-photon source for quantum networks.