Epitaxial Er-doped Y2O3 on silicon for quantum coherent devices

Manish Kumar Singh,Jianguo Wen,Gary Wolfowicz,David D Awschalom,Tijana Rajh,Yizhong Huang,Tian Zhong,Supratik Guha,Abhinav Prakash

doi:10.1063/1.5142611

Manish Kumar Singh, Jianguo Wen + Show 7 more

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https://doi.org/10.1063/1.5142611

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Abstract

Rare-earth ions (REIs) have incomplete 4f shells and possess narrow optical intra-4f transitions due to shielding from electrons in the 5s and 5p orbitals, making them good candidates for solid-state optical quantum memory. The emission of Er3+ in the telecom C-band (1530 nm–1565 nm) makes it especially attractive for this application. In order to build practical, scalable devices, the REI needs to be embedded in a non-interacting host material, preferably one that can be integrated with silicon. In this paper, we show that Er3+ can be isovalently incorporated into epitaxial Y2O3 thin films on Si (111). We report on the synthesis of epitaxial, single-crystalline Er:Y2O3 on Si with a narrow inhomogeneous linewidth in the photoluminescence (PL) spectra, 5.1 GHz (&lt;100 mK), and an optical excited state lifetime of 8.1 ms. The choice of Y2O3 was driven by its low nuclear spin and small lattice mismatch with Si. Using PL and electron paramagnetic resonance, we show that Er3+ substitutes for Y in the crystal lattice. The role of interfacial SiOx, diffusion of silicon into the film, and the effect of buffer layers on the inhomogeneous PL linewidth are examined. We also find that the linewidth decreased monotonically with film thickness but surprisingly exhibits no correlation with the film crystalline quality, as measured by the x-ray rocking curve scans, suggesting other factors at play that limit the inhomogeneous broadening in Y2O3 films.

Highlights

The need for quantum memory devices has been increasingly apparent in networked coherent quantum systems that use an optical quantum communication link within a distributed network of processors or a secure communication network that uses quantum repeaters.1–3 The role of a quantum memory is to store quantum information during entanglement events, and multiple mechanisms and systems for storage have been identified by researchers.4,5 A promising and convenient approach among them is to use the spin-optical interfaces of rare-earth ions (REIs).6–10 Rare-earth ions have full 5s and 5p orbitals that shield the inner 4f levels from the local environment, resulting in narrow 4f −4f electronic transitions
The film with x = 0.17 had the smallest lattice mismatch (0.37%) with silicon. This film has lower lattice mismatch compared to the unalloyed film (0.37% vs 2.4%), the inhomogeneous linewidth was found to be 7× larger [Figs. 4(j)–4(l)]. This broadening is attributed to the presence of random substitutional disorder in the film due to La substituting at the Y site similar to the results reported for Sc alloyed Er-doped Y2O3 (Er):Y2O342 and Eu:Y2O3.43 Increasing the amount of La (x = 0.24) further increases the inhomogeneous linewidth due to enhanced disorder as well as phase segregation of hexagonal La2O3, as evidenced by an additional diffraction peak in the corresponding 2θ–ω scan
We have successfully demonstrated the growth of Er:Y2O3 epitaxial thin films on Si(111) and using spectroscopic techniques demonstrated the erbium substitutes for yttrium in the bixbyite structure at both the C2 and C3i sites where the optical decay lifetime obtained for the C2 sites is comparable to that of bulk single crystals

Summary

Introduction

The need for quantum memory devices has been increasingly apparent in networked coherent quantum systems that use an optical quantum communication link within a distributed network of processors or a secure communication network that uses quantum repeaters. The role of a quantum memory is to store quantum information during entanglement events, and multiple mechanisms and systems for storage have been identified by researchers. A promising and convenient approach among them is to use the spin-optical interfaces of rare-earth ions (REIs). Rare-earth ions have full 5s and 5p orbitals that shield the inner 4f levels from the local environment, resulting in narrow 4f −4f electronic transitions. Rare-earth ions have full 5s and 5p orbitals that shield the inner 4f levels from the local environment, resulting in narrow 4f −4f electronic transitions. This shielding results in a low spectral diffusion not achievable in other systems such as the nitrogen-vacancy center defects.. This shielding results in a low spectral diffusion not achievable in other systems such as the nitrogen-vacancy center defects.9 They are well suited for the development of coherent microwave to optical transduction.. They are well suited for the development of coherent microwave to optical transduction.11 These properties make REIs ideal for solid-state optical quantum memory systems, provided they can be embedded in a sufficiently inert (low nuclear spin and no unpaired electrons) solid-state host material and are capable of being modulated electrically or optically in an efficient manner.

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