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EPJ Web of Conferences

Hybrid optical quantum technology platform: Y 2 SiO 5 bonded on glass and Dry-etched waveguides

A. Talneau, Mickael Chan, Alban Ferrier, Perrine Berger, Sacha Welinski

Published Jan 1, 2026• 0 citations
Publisher

Abstract

A Y2SiO5 bonded on glass hybrid photonic platform is here investigated, for enhancing the optical guided mode interaction with active rare-earth ions. The main challenging technological fabrication steps: bonding and waveguide dry-etching, are reported and discussed. Tailored optical waveguide design is proposed to accommodate technological fabrication constrains.

DOI
10.1051/epjconf/202638902013

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A Y2SiO5 bonded on glass hybrid photonic platform is here investigated, for enhancing the optical guided mode interaction with active rare-earth ions. The main challenging technological fabrication steps: bonding and waveguide dry-etching, are reported and discussed. Tailored optical waveguide design is proposed to accommodate technological fabrication constrains.
For high‐efficiency optical quantum technology platforms, bonding rare‐earth doped crystals on glass are of great interest, enabling the enhancement of the optical guided mode interaction with the active rare‐earth ions. Optical coherence lifetimes and stable operation are operated at very low temperature (3–4 K). Bonding should be preferably performed without adding any intermediate sticking layer in order not to hamper the optical mode distribution and propagation. Directly bonded Y2SiO5 crystal on a borosilicate glass is shown and the bonding mechanisms are discussed.
With an assortment of narrow line-width transitions spanning the visible and IR spectrum and long spin coherence times, rare-earth doped crystals are the leading material system for solid-state quantum memories. Integrating these materials in an on-chip optical platform would create opportunities for highly integrated light-matter interfaces for quantum communication and quantum computing. Nano-photonic resonators with high quality factors and small mode volumes are required for efficient on-chip coupling to the small dipole moment of rare-earth ion transitions. However, direct fabrication of optical cavities in these crystals with current nanofabrication techniques is difficult and unparallelized, as either exotic etch chemistries or physical milling processes are required. We fabricated hybrid devices by mechanically transferring a nanoscale membrane of gallium arsenide (GaAs) onto a neodymium-doped yttrium silicon oxide (Y2SiO5) crystal and then using electron beam lithography and standard III-V dry etching to pattern nanobeam photonic crystal cavities and ring resonator cavities, a technique that is easily adapted to other frequency ranges for arbitrary dopants in any rare earth host system. Single crystalline GaAs was chosen for its low loss and high refractive index at the transition wavelength. We demonstrated the potential to evanescently couple between the cavity field and the 883 nm 4I9/2- 4F3/2 transition of nearby neodymium impurities in the host crystal by examining transmission spectra through a waveguide coupled to the resonator with a custom-built confocal microscope. The prospects and requirements for using this system for scalable quantum networks are discussed.
Coherent quantum devices play a central role in quantum science and engineering. Rare-earth ions such as erbium in solids feature numerous 4f- intra-shell transitions that are effectively shielded from their crystalline surroundings by closed outer shells, allowing for long spin coherence times and narrow optical transitions. Recent ensemble experiments have established the rare-earth doped crystals as the leading materials for optical quantum memories. However, the development of large-scale quantum devices based on rare-earth doped materials has remained a challenge. Here we describe a scalable quantum photonic platform based on epitaxially grown oxide thin films doped with trivalent ions on silicon substrates. The platform builds upon the recent developments of high quality epitaxial rare-earth doped oxides on silicon, and highlights the integration of quantum coherent materials with existing silicon technologies for ultimate device scalability. The proposed device platform builds upon our capability to epitaxially grow high quality, near-lattice-matched Y2O3 thin films on silicon. The epitaxial thin film is of high structural quality and offers several distinct advantages: (1) significantly less optical loss and better quantum emitter coherence; (2) atomic precision placement of rare-earth emitters (via delta doping) with respect to the photonic mode for controllable ion-photon coupling; (3) scalable top-down device fabrication using standard lithography and etching techniques; (4) heterogeneous integration with silicon takes full advantage of existing silicon photonics technologies for routing, tuning, and modulation of the quantum emission from rare-earth ions.
Rare earth ions are known as promising candidates for building quantum light-matter interface. However, tunable photonic cavity access to rare earth ions in their desired host crystal remains challenging. Here, we demonstrate the integration of erbium doped yttrium orthosilicate (Er3+:Y2SiO5) with thin-film lithium niobate photonic circuit by plasma-activated direct flip chip bonding. Resonant coupling to erbium ions is realized by on-chip electro-optically tuned high Q lithium niobate micro-ring resonators. Fluorescence and absorption of erbium ions at 1536.48 nm are measured in the waveguides, while the collective ion-cavity cooperativity with micro-ring resonators is assessed to be 0.36. This work presents a versatile scheme for future rare earth ion integrated quantum devices.
This paper presents progress in developing crystalline waveguides to enable efficient and integrated quantum memories for long-distance quantum communications. The primary objective is to overcome low light-matter interaction strength encountered in rare-earth ion (REI) doped crystals, particularly Yttrium Orthosilicate (YSO), which limits optical storage efficiencies. Compared to other strategies toward photonic integration, our novel approach utilizes traditional lithography and dry-etching techniques to retain the beneficial properties of bulk crystals while allowing for design flexibility. Bonding, lapping, polishing, and dry-etching processes were optimized to fabricate the suitable YSO waveguide geometry demonstrated by simulations. This research paves the way toward fully integrated quantum repeaters. It also contributes toward integration for other REI-doped crystals-based quantum technologies such as quantum computing, single photon generation, RF spectral analysis, and microwave-to-optical quantum transduction.