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NTT technical review

Rare-earth Epitaxial Films as a Platform for Quantum Information Manipulation

Takehiko Tawara, Hiroo Omi

Published Sep 1, 2014• 1 citation
Publisher

Abstract

Rare-earth ions in a solid form have discrete energy levels peculiar to the ionic species, and they are therefore expected to become an excellent platform material for quantum information manipulation.A promising candidate for this purpose is rare-earth epitaxial film such as erbium oxide (Er 2 O 3 ) film grown on a silicon substrate.This article describes the high-quality crystal growth and excellent optical characteristics of Er 2 O 3 epitaxial films for quantum information devices.

DOI
10.53829/ntr201409fa4

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Rare-earth ions in a solid form have discrete energy levels peculiar to the ionic species, and they are therefore expected to become an excellent platform material for quantum information manipulation.A promising candidate for this purpose is rare-earth epitaxial film such as erbium oxide (Er 2 O 3 ) film grown on a silicon substrate.This article describes the high-quality crystal growth and excellent optical characteristics of Er 2 O 3 epitaxial films for quantum information devices.
Erbium (Er) is a rare-earth element that is expected to be a platform for manipulation of quantum information by utilizing telecommunication-wavelength photons.However, high-quality epitaxial growth of Er-doped host crystals is difficult, and the memory time of quantum information, which determines the performance of quantum manipulation, is much shorter than theoretically predicted.We investigated a good-compatibility rare-earth oxide as a host crystal for Er.The host oxide crystal, cerium oxide (CeO 2 ), had its nuclear spin removed (i.e., magnetically purified).The nuclear spin is the main factor that shortens the lifetime of quantum-information retention time.In this article, we describe high-quality epitaxial growth of CeO 2 and its optical properties as a thin film grown on a silicon substrate.
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.
The obtention of quantum-grade rare-earth-doped oxide thin films that can be integrated with optical cavities and microwave resonators is of great interest for the development of scalable quantum devices. Among the different growth methods, chemical vapor deposition (CVD) offers high flexibility and has demonstrated the ability to produce oxide films hosting rare-earth ions with narrow linewidths. However, growing epitaxial films directly on silicon is challenging by CVD due to a native amorphous oxide layer formation at the interface. In this manuscript, we investigate the CVD growth of erbium-doped yttrium oxide (Er:Y2O3) thin films on different substrates, including silicon, sapphire, quartz, or yttria stabilized zirconia (YSZ). Alternatively, growth was also attempted on an epitaxial Y2O3 template layer on Si (111) prepared by molecular beam epitaxy (MBE) in order to circumvent the issue of the amorphous interlayer. We found that the substrate impacts the film morphology and the crystalline orientations, with different textures observed for the CVD film on the MBE-oxide/Si template (111) and epitaxial growth on YSZ (001). In terms of optical properties, Er3+ ions exhibit visible and IR emission features that are comparable for all samples, indicating a high-quality local crystalline environment regardless of the substrate. Our approach opens interesting prospects to integrate such films into scalable devices for optical quantum technologies.
The obtention of quantum-grade rare-earth doped oxide thin films that can be integrated with optical cavities and microwave resonators is of great interest for the development of scalable quantum devices. Among the different growth methods, Chemical Vapour Deposition (CVD) offers high flexibility and has demonstrated the ability to produce oxide films hosting rare-earth ions with narrow linewidths. However, growing epitaxial films directly on silicon is challenging by CVD due to a native amorphous oxide layer formation at the interface. In this manuscript, we investigate the CVD growth of erbium-doped yttrium oxide (Er:Y2O3) thin films on different substrates, including silicon, sapphire, quartz or yttria stabilized zirconia (YSZ). Alternatively, growth was also attempted on an epitaxial Y2O3 template layer on Si (111) prepared by molecular beam epitaxy (MBE) in order to circumvent the issue of the amorphous interlayer. We found that the substrate impacts the film morphology and the crystalline orientations, with different textures observed for the CVD film on the MBE-oxide/Si template (111) and epitaxial growth on YSZ (001). In terms of optical properties, Er3+ ions exhibit visible and IR emission features that are comparable for all samples, indicating a high-quality local crystalline environment regardless of the substrate. Our approach opens interesting prospects to integrate such films into scalable devices for optical quantum technologies.