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Conference on Lasers and Electro-Optics

Correlated optical-spin coherence spectroscopy on telecom-wavelength epitaxial rare-earth qubits

Yizhong Huang, Shobhit Gupta, Natasha Tomm, Richard John Warburton, Tian Zhong

Published Jan 1, 2022• 1 citation
Publisher

Abstract

We perform correlated optical-spin coherence spectroscopy on epitaxial rare-earth qubits in an oxide thin film. Single Er3+ ions are optically addressed and used to probe coupling to two-level-systems as a simultaneous optical-spin decoherence mechanism.
DOI
10.1364/cleo_qels.2022.fm5d.3

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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.
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Harnessing rare-earth ions in oxides for quantum networks requires integration with bright emitters in III-V semiconductors, but local disorder and interfacial noise limit their optical coherence. Here, we investigate the microscopic origins of the ensemble spectrum in Er3+^{3+}3+:TiO2_22​ epitaxial thin films on GaAs and GaSb substrates. Ab initio calculations combined with noise-Hamiltonian modeling and Monte Carlo simulations quantify the effects of interfacial and bulk spin noise and local strain on erbium crystal-field energies and inhomogeneous linewidths. Photoluminescence excitation spectroscopy reveals that Er3+^{3+}3+ ions positioned at increasing distances from the III-V/oxide interface produce a systematic blue shift of the Y1→Z1Y_1\rightarrow Z_1Y1​→Z1​ transition, consistent with strain relaxation predicted by theory. Thermal annealing produces a compensating redshift and linewidth narrowing, isolating the roles of oxygen-vacancy and gallium-diffusion noise. These results provide microscopic insight into disorder-driven decoherence, offering pathways for precise control of hybrid quantum systems for scalable quantum technologies.
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.