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arXiv:2508.12429

Spin decoherence dynamics of Er$^{3+}$ in CeO$_2$ film

Sagar Kumar Seth, Jonah Nagura, Vrindaa Somjit, Bapat, Aneesh, Xinhao Li, Gregory D. Grant, Ignas Masiulionis, Xu Han, F. Joseph Heremans, Giulia Galli, D. D. Awschalom, Supratik Guha, Jiefei Zhang

Published Aug 17, 2025• 0 citations
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Abstract

Developing telecom-compatible spin-photon interfaces is essential towards scalable quantum networks. Erbium ions (Er$^{3+}$) exhibit a unique combination of a telecom (1.5 $μ$m) optical transition and an effective spin-$1/2$ ground state, but identifying a host that enables heterogeneous device integration while preserving long optical and spin coherence remains an open challenge. We explore a new platform of Er$^{3+}$:CeO$_2$ films on silicon, offering low nuclear spin density and the potential for on-chip integration. We demonstrate a 38.8 $μ$s spin coherence, which can be extended to 176.4\nobreakspace $μ$s with dynamical decoupling. Pairing experiments with cluster correlation expansion calculations, we identify spectral diffusion-induced Er$^{3+}$ spin flips as the dominant decoherence mechanism and provide pathways to millisecond-scale coherence.

DOI
10.48550/arxiv.2508.12429

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Spin decoherence dynamics of Er3+^{3+}3+ in CeO2_22​ film
Developing telecom-compatible spin-photon interfaces is essential towards scalable quantum networks. Erbium ions (Er3+^{3+}3+) exhibit a unique combination of a telecom (1.5 μμμm) optical transition and an effective spin-1/21/21/2 ground state, but identifying a host that enables heterogeneous device integration while preserving long optical and spin coherence remains an open challenge. We explore a new platform of Er3+^{3+}3+:CeO2_22​ films on silicon, offering low nuclear spin density and the potential for on-chip integration. We demonstrate a 38.8 μμμs spin coherence, which can be extended to 176.4\nobreakspace μμμs with dynamical decoupling. Pairing experiments with cluster correlation expansion calculations, we identify spectral diffusion-induced Er3+^{3+}3+ spin flips as the dominant decoherence mechanism and provide pathways to millisecond-scale coherence.
Developing telecom-compatible spin-photon interfaces is essential towards scalable quantum networks. Erbium ions (Er^{3+}) exhibit a unique combination of a telecom (1.5 μm) optical transition and an effective spin-1/2 ground state, but identifying a host that enables heterogeneous device integration while preserving long optical and spin coherence remains an open challenge. We explore the potential of Er^{3+}:CeO_{2} films on silicon and study the Er^{3+} spin coherence, offering low nuclear spin density and the potential for on-chip integration. We demonstrate a 38.8 μs spin coherence, which can be extended to 176.4 μs with dynamical decoupling. Pairing experiments with cluster correlation expansion calculations, we identify spectral diffusion induced by bath Er^{3+} spin flip-flops as the dominant decoherence mechanism and provide pathways to millisecond-scale coherence.
Clock-transition-enabled long electron spin coherence of telecom emitters in CeO2_22​
Rare-earth-ion-doped crystals has emerged as a promising platform for quantum technologies, owing to their narrow telecom-band optical emission, long spin memory, and compatibility with silicon integrated photonic architectures. However, the realization of scalable quantum devices requires host materials with intrinsically dilute spin environments to suppress decoherence. In this context, erbium (Er3+^{3+}3+) doped cerium oxide (CeO2_22​) is an attractive candidate due to the ultra-low concentration of nuclear spins in the host matrix and its compatibility with silicon-based technologies. Here we perform a comprehensive investigation of the coherence properties of Er3+^{3+}3+ electron spin qubit in CeO2_22​ via semiclassical as well as detailed cluster correlation expansion simulations. By systematically exploring magnetic field strength, pulse sequences, erbium concentration, and spin temperature, we identify regimes where decoherence from the spin bath is strongly suppressed. Our investigations illustrate that at dilute doping concentration (of the order of 10 ppb) and sub-Kelvin temperatures, operation near clock transitions enables Hahn-echo coherence times to approach the second timescale even at natural isotopic abundance. Importantly, from a practical standpoint, coherence times on the order of ∼10\sim 10∼10 ms are expected even at liquid helium temperature (about 2 K) for similar concentrations. Moreover, we demonstrate that an additional enhancement can be obtained with conventional multi-πππ-pulse dynamical decoupling protocols. Thus, our findings establish Er3+^{3+}3+ doped CeO2_22​ as a front-runner for realizing spin qubits, quantum memories, and integrated quantum networks.
Robust spin-photon interfaces with optical transitions in the telecommunication band are essential for quantum networking technologies. Erbium (Er) ions are the ideal candidate with environmentally protected transitions in telecom-C band. Finding the right technologically compatible host material to enable long-lived spins remains a major hurdle. We introduce a new platform based on Er ions in cerium dioxide (CeO 2 ) as a nearly-zero nuclear spin environment (0.04%) epitaxially grown on silicon, offering silicon compatibility for opto-electrical devices. Our studies focus on Er 3+ ions and show a narrow homogeneous linewidth of 440 kHz with an optical coherence time of 0.72 μs at 3.6 K. The reduced nuclear spin noise enables a slow spin-lattice relaxation with a spin relaxation time up to 2.5 ms and an electron spin coherence time of 0.66 μs (in the isolated ion limit) at 3.6 K. These findings highlight the potential of Er 3+ :CeO 2 platform for quantum networks applications.
Rare-earth ion dopants in solid-state hosts are ideal candidates for quantum communication technologies, such as quantum memories, due to the intrinsic spin–photon interface of the rare-earth ion combined with the integration methods available in the solid state. Erbium-doped cerium oxide (Er:CeO2) is a particularly promising host material platform for such a quantum memory, as it combines the telecom-wavelength (∼1.5μm) 4f–4f transition of erbium, a predicted long electron spin coherence time when embedded in CeO2, and a small lattice mismatch with silicon. In this work, we report on the epitaxial growth of Er:CeO2 thin films on silicon using molecular beam epitaxy, with controlled erbium concentration between 2 and 130 parts per million (ppm). We carry out a detailed microstructural study to verify the CeO2 host structure and characterize the spin and optical properties of the embedded Er3+ ions as a function of doping density. In as-grown Er:CeO2 in the 2–3 ppm regime, we identify an EPR linewidth of 245(1) MHz, an optical inhomogeneous linewidth of 9.5(2) GHz, an optical excited state lifetime of 3.5(1) ms, and a spectral diffusion-limited homogeneous linewidth as narrow as 4.8(3) MHz. We test the annealing of Er:CeO2 films up to 900 °C, which yields narrowing of the inhomogeneous linewidth by 20% and extension of the excited state lifetime by 40%.
Long-range quantum network nodes require the combination of strong light-matter coupling, long coherence times and in situ spectral control at telecom wavelengths. The coherence of erbium in integrated devices is held back by its hosts, which do not simultaneously provide the weakly magnetic nuclear-spin environment and the well-defined substitutional sites found in coherence-optimised bulk crystals. Here we bring such an optimised crystal onto a photonic chip, by bonding an Er3+{^{3+}}3+:CaWO4{_{4}}4​ host without an adhesive interlayer to a high-Q{Q}Q electro-optically tuneable thin-film lithium niobate microring resonator. At an effective temperature of 75{75}75 mK and a field of only 0.2{0.2}0.2 T, the bonded ensemble retains an effective homogeneous linewidth of 289±34{289\pm34}289±34 Hz (TM=1.10±0.13{T_\text{M}=1.10\pm0.13}TM​=1.10±0.13 ms), with spectral diffusion proceeding at 86±18{86\pm18}86±18 Hz and saturating at 1.5±0.2{1.5\pm0.2}1.5±0.2 kHz. Electro-optically tuning the resonator through the erbium optical transition resolves an avoided crossing with a collective cooperativity of C=6.7±0.4{C=6.7\pm0.4}C=6.7±0.4. Exploiting superhyperfine coupling to the host's 183{^{183}}183W nuclear spins, we store and retrieve optical phase information over 5{5}5 s with a visibility of 0.935±0.015{0.935\pm0.015}0.935±0.015. Strong collective coupling, millisecond coherence and in situ spectral tuning in a single device thus establish heterogeneous integration leveraging coherence-optimised hosts as a route to scalable telecom quantum networks.
Optically active solid-state spin qubits thrive as an appealing technology for quantum interconnects and quantum networks, thanks to their atomic size, scalable synthesis, long-lived coherence, and ability to coherently interface with flying qubits. Trivalent erbium dopants, in particular, emerge as an attractive candidate due to their emission in the telecom C band and shielded 4f intra-shell spin and optical transitions. Nevertheless, prevailing top-down architectures for rare-earth qubits and devices have not yet achieved simultaneous long optical and spin coherence, which is necessary for efficient long-distance quantum networks. Here, we demonstrate dual Er3+ telecom spin-photon interfaces in two distinct lattice symmetry sites within an epitaxial thin-film platform. By leveraging high matrix crystallinity, controlled proximity of dopants to surfaces, and exploiting host lattice symmetry, we simultaneously achieve kilohertz-level optical linewidth in a strongly symmetry-protected site, and erbium qubit spin coherence times exceeding 10 milliseconds. Additionally, we realize single-shot readout and microwave coherent control of erbium qubits in a fiber-integrated package, enabling rapid deployment and scalability. These advancements highlight the significant potential of high-quality rare-earth qubits and quantum memories assembled using a bottom-up method, paving the way for scalable development of quantum light-matter interfaces tailored for telecommunication quantum networks. Erbium quantum emitters operating in the telecom C band are promising for spin-photon interfaces but achieving both optical and spin coherence has been challenging. Gupta et al. report two types of erbium dopants in epitaxial Y2O3 thin films occupying distinct lattice sites and exhibiting long spin and optical coherence times