(Invited) Simple and Optimized Silicon Nano-Antennas for Quantum Emitter Control

Abstract

Improving the brightness and efficiency of single photon sources by the mean of optically resonant nanostructures is a major stake for the development of efficient nanodevices for quantum communications.For a couple of decades, these resonant nanostructures have mainly been made of noble metal that sustain strong localized resonances (LSPR) that can be used to manipulate, concentrate or redirect visible light. Such properties have led to numerous actual or potential applications in integrated optics, sensors, nonlinear optics, field-enhanced spectroscopies, or photovoltaics. Recently, an alternative emerged with high refractive index dielectric nanostructures, which offer the same range of applications as plasmonics by manipulating Mie optical resonances instead of LSPR [1].These resonances can be efficiently tuned by modifying the size, shape, and material of those nanostructures (e.g. silicon, n ~ 4) [2]. Furthermore, high index dielectric nanostructures offer several key advantages when compared to their metallic counterparts: absorption losses are far weaker for wavelengths longer than the direct band gap, access to semiconductor (CMOS) technology for nanostructure fabrication, and presence of intrinsic strong magnetic and electric resonances, providing an unique opportunity to spatially separate and redistribute the energy of the magnetic and electric parts of the electromagnetic field in the near field, otherwise inextricably connected in the far field [3].We discuss here the effect of simple high-index dielectric nanoantennas on the spontaneous emission of model quantum emitters. First, we accurately positioned arrays of nanodiamonds hosting NV colored centers in the gap of silicon dimer nanoantennas, using atomic force microscopy (AFM – [4]) nanoxerography [5]. The NV center is an ideal model system exhibiting single photon emission properties at room temperature, which is well adapted for proof of concept experiments in quantum nano-optics. Since the local density of photonic states (LDOS) is modified by the nanostructure, we show by the mean of time-resolved photoluminescence acquisitions that the photodynamics of these quantum emitters can be enhanced by the coupling to the nanoantenna, down to the single photon emission regime [5]. Our experimental results are in good agreement with multipolar analysis and numerical simulations based on the Green Dyadic Method - GDM.Second, in order to go a step further, we explore the control of the directive emission from quantum dipolar sources by the mean of complex silicon antennas. The latter, made of a given number of building (nano)blocks, are optimized by an Evolutionary Algorithm (EA) coupled to full-field electrodynamical GDM simulations. The geometries obtained allow to tailor the emission direction of a single dipolar source, maximizing the intensity of the emitted light within a given solid angle. Our numerical and preliminary experimental results demonstrate the efficiency of such compact EA-optimized antennas for the control of quantum nanosources. Acknowledgements : This work was supported by Programme Investissements d’Avenir through the grants ANR-10-LABX-0037-NEXT (MILO) and NanoX n° ANR-17-EURE- 0009 (Q-META), by the HiLight ANR project ANR-19-CE24-0026, by LAAS-CNRS micro and nanotechnologies platform member of the French Renatech network, by the CNRS and INSA (PhD grant), by the Région Midi-Pyrénées via the Institute for Quantum technologies in Occitanie (IQO), and by the computing facility center CALMIP of the University of Toulouse under grants P12167 and P1107. References : Kallel et al, Tunable enhancement of light absorption and scattering in Si1xGex nanowires, Phys. Rev. B 12: 085318, 2012.P.R. Wiecha et al., Strongly directional scattering from dielectric nanowires, ACS Photonics 4: pp 2036–2046, 2017.Montagnac et al., Control of light emission of quantum emitters coupled to silicon nanoantenna using cylindrical vector beams, Light : Science and Applications 12 (1), 239, 2023.Humbert et al., Versatile, rapid and robust nanopositioning of single-photon emitters by AFM-nanoxerography, Nanotechnology 33, 215301, 2022.Humbert et al., Large-scale controlled coupling of single-photon emitters to high index dielectric nanoantennas using AFM nanoxerography, Nanoscale 15, 599-608, 2023. Figure 1