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arXiv:2310.07120

Dual epitaxial telecom spin-photon interfaces with correlated long-lived coherence

Shobhit Gupta, Yizhong Huang, Shihan Liu, Yuxiang Pei, Natasha Tomm, Richard John Warburton, Tian Zhong

Published Oct 11, 2023• 3 citations
arXivHTMLPDF

Abstract

Optically active solid-state spin qubits thrive as an appealing technology for quantum interconnect and quantum networking, owing to their atomic size, scalable creation, long-lived coherence, and ability to coherently interface with flying qubits. Trivalent erbium dopants in particular emerge as a compelling candidate with their telecom C band emission and shielded 4f intra-shell spin-optical transitions. However, prevailing top-down architecture for rare-earth qubits and devices has not allowed simultaneous long optical and spin coherence necessary for long-distance quantum networks. Here we demonstrate dual erbium telecom spin-photon interfaces in an epitaxial thin-film platform via wafer-scale bottom-up synthesis. Harnessing precise controls over the matrix purity, dopant placement, and symmetry unique to this platform, we simultaneously achieve millisecond erbium spin coherence time and $<$3 kilohertz optical dephasing rate in an inversion-symmetry protected site and realize both optical and microwave control in a fiber-integrated package for rapid scaling up. These results demonstrate a significant prospect for high-quality rare-earth qubits and quantum memories assembled using a bottom-up method and pave the way for the large-scale development of quantum light-matter interfaces for telecommunication quantum networks.

DOI
10.48550/arxiv.2310.07120

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Optically active solid-state spin qubits thrive as an appealing technology for quantum interconnect and quantum networking, owing to their atomic size, scalable creation, long-lived coherence, and ability to coherently interface with flying qubits. Trivalent erbium dopants in particular emerge as a compelling candidate with their telecom C band emission and shielded 4f intra-shell spin-optical transitions. However, prevailing top-down architecture for rare-earth qubits and devices has not allowed simultaneous long optical and spin coherence necessary for long-distance quantum networks. Here we demonstrate dual erbium telecom spin-photon interfaces in an epitaxial thin-film platform via wafer-scale bottom-up synthesis. Harnessing precise controls over the matrix purity, dopant placement, and symmetry unique to this platform, we simultaneously achieve millisecond erbium spin coherence time and <<<3 kilohertz optical dephasing rate in an inversion-symmetry protected site and realize both optical and microwave control in a fiber-integrated package for rapid scaling up. These results demonstrate a significant prospect for high-quality rare-earth qubits and quantum memories assembled using a bottom-up method and pave the way for the large-scale development of quantum light-matter interfaces for telecommunication quantum networks.
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We report dual er qubits in two distinct symmetry sites of an epitaxially grown single crystal Y2O3 thin film. Coupling of Er spins to a superconducting microwave resonator and a fiber micro-cavity enables simultaneous optical-spin coherence spectroscopy at millikelvin temperature. At optimal field orientations, over millisecond spin coherence times are observed for Er qubits in both C2 and C3i symmetry sites. Single Er ions in both C2 and C3i sites are addressed optically, respectively at the field configuration where their millisecond spin coherence times are measured. By correlating the spin spectral diffusion and optical dephasing rate of C3i Er qubits, we report a magnetic noise limited spin-optical dephasing rate of only 2.6 kHz, demonstrating significant prospect of Er in epitaxial Y2O3 thin film as a highly coherent spin-photon interface for quantum network.
Quantum nanophotonics interfacing optical photons with coherent atomic spins have the potential to revolutionize secure communications, ultra-scale sensing, distributed quantum computing, and enhanced metrology, but currently lack scalable material and device platform necessary for building robust quantum light-matter interfaces. The trivalent rare-earth ion such as erbium (Er3+) is a promising candidate for quantum interfaces because of its narrow optical transition as well as a long spin coherence time. Here, we present an epitaxial Er3+:Y2O3 on silicon platform for scalable quantum light-matter interconnect, enabling efficient spin-photon interfaces based on individual rare-earth qubits and quantum transduction via ensembles of ions.
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.
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.
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.