Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2210.13793

Microwave-optical double resonance in a erbium-doped whispering-gallery-mode resonator

Ma, Li, Luke S. Trainor, Gavin G. G. King, Harald G. L. Schwefel, Jevon J. Longdell

Published Oct 25, 2022• 0 citations
arXivHTMLPDF

Abstract

We showcase an erbium-doped whispering-gallery-mode resonator with optical modes that display intrinsic quality factors better than $10^8$ (linewidths less than 2 MHz), and coupling strengths to collective erbium transitions of up to 2$π\times$1.2 GHz - enough to reach the ensemble strong coupling regime. Our optical cavity sits inside a microwave resonator, allowing us to probe the spin transition which is tuned by an external magnetic field. We show a modified optically detected magnetic resonance measurement that measures population transfer by a change in coupling strength rather than absorption coefficient. This modification was enabled by the strong coupling to our modes, and allows us to optically probe the spin transition detuned by more than the inhomogeneous linewidth. We contrast this measurement with electron paramagnetic resonance to experimentally show that our optical modes are confined in a region of large microwave magnetic field and we explore how such a geometry could be used for coherent microwave-optical transduction.

DOI
10.48550/arxiv.2210.13793

Related papers

Optically detected magnetic resonance to characterize atomlike microwave-optical transducers

Li Ma, Luke S. Trainor, Gavin G. G. King +2 more

We introduce a method for optically detected magnetic resonance for atomlike systems in an optical resonator. Driving the spin transitions of these systems with microwaves causes changes to the populations of the ground-state spin levels, which we detect by changes in the optical cavity frequency. The technique is useful for characterizing experiments aimed at quantum microwave-to-optical transduction because it provides a way of only probing the spin transitions of the atomlike systems that are in the optical resonator's mode. We demonstrate the technique using a cryogenic erbium-doped whispering-gallery-mode resonator inside a microwave resonator. We compare our results with more standard electron paramagnetic resonance to show that our optical modes are confined to a region of large microwave magnetic-field amplitude. Our optical modes have a $Q$ factor better than ${10}^{8}$ making them the highest $Q$-factor resonators studied with cryogenic rare-earth-ion dopants, allowing us to report ensemble strong coupling between the erbium dopants and an optical whispering-gallery-mode resonator.

Physical Review A•May 15, 2023•3 citations

Realization of strong coupling between Er3+: CaWO4 crystal and the loop-gap resonator for a hybrid quantum system

Q. Li, Miaomiao Ren, Shuping Liu +2 more

Erbium-doped crystals provide a promising platform for integration with other quantum systems, offering telecom-band optical and microwave spin transitions with long coherence times for quantum memory and transduction applications. In order to construct efficient hybrid quantum systems, it is challenging but necessary to realize strong coupling between erbium spins and other microwave photons. Here, we design and construct a high-quality-factor three-dimensional loop-gap microwave resonator for wide-range electron spin resonance detection. We achieved strong coupling with a strength of 85.1 MHz at 100 mK. Our results demonstrate a viable hybrid quantum system, paving the way for integrated networks that combine optical communication with microwave quantum computing.

Applied Physics Letters•Sep 15, 2025•1 citation

Coherent microwave-to-optical transduction with Yb:YSO spins strongly coupled to a 3D resonator

Ujjwal Gautam, Nasser Gohari Kamel, Sourabh Kumar +1 more

Microwave-to-optical quantum transducers are essential for entangling remote superconducting qubits. Among the available transduction platforms, ensembles of Er$^{3+}$ and Yb$^{3+}$ ions doped into solids have emerged as leading candidates. While external magnetic fields are needed to split the Zeeman levels of erbium ions and enable a microwave--qubit interface, superconducting qubits suffer decoherence in such fields. In contrast, ytterbium ions exhibit zero-first-order Zeeman transitions and large hyperfine splittings at zero magnetic field (when doped into inorganic crystals). Owing to its long optical and spin coherence times, Yb:YSO has been widely used as a quantum memory, yet its potential for quantum transduction remains largely unexplored. Investigating this material could enable the integration of quantum memory and transduction in a single platform. Here, we demonstrate microwave-to-optical transduction in the continuous-wave regime using a 5\,ppm doped Yb:YSO crystal. The internal transduction efficiency is $2\times10^{-8}$ with a bandwidth of 200\,kHz, achieved using a 3D loop-gap microwave resonator (LGR) and a single-pass optical configuration. We explore all the ground states that form a V-type three-level system with the first and second optical excited states and assert the use of the ground state, which provides the highest efficiency and isolated optical transition. We further establish strong spin-microwave coupling from avoided crossing measurements. With a strong microwave drive to saturate the spin transition, we estimate the spin population pumped into the excited state, close to the simulated value. Finally, we calculate target parameter values for maximum efficiency with our system and suggest using 50\,ppm doped Yb:YSO crystal. With the calculated target parameters, the internal transduction efficiency is predicted to reach up to $10^{-4}$ in the current LGR.

quant-pharXiv:2609.02226•Sep 3, 2026•0 citations

Optical-Coupling of distant spins via collective enhancement in multi-mode whispering gallery resonators

Daniel Lombardo, Jason Twamley

The quantum coupling of spatially distant spins via optical photons using cavity quantum electrodynamic (cQED) methods has proved experimentally challenging due to the large spin-photon coupling strengths required. To achieve such coupling strengths using traditional cQED methods requires either individual spins and ultra-small cavities or an ensemble of identical spins coupled to larger cavities. In this work we describe a method to couple distant spins via the collective enhanced coupling to a large ensemble ∼ N, of degenerate optical Whispering Gallery Modes (WGM) in a spherical resonator where the spins are spatially located at the antipodes. The setup can be scaled-up to build 1D, 2D and 3D cQED lattices to enable quantum simulation or computing.

Optics Express•Feb 2, 2015•0 citations

Coupling of an erbium spin ensemble to a superconducting resonator

M. U. Staudt, I.-C. Hoi, Philip Krantz +9 more

A quantum coherent interface between optical and microwave photons can be used as a basic building block within a future quantum information network. The interface is envisioned as an ensemble of rare-earth ions coupled to a superconducting resonator, allowing for coherent transfer between optical and microwave photons. Towards this end, we have realized a hybrid device coupling a Er3+-doped Y2SiO5 crystal in a superconducting coplanar waveguide cavity. We observe a collective spin coupling of 4 MHz and a spin linewidth of down to 75 MHz.

•Jan 1, 2012•11 citations

Light–atom interaction in an Er:YSO whispering gallery mode resonator

Trevor Kling, Mahdi Hosseini

Rare-earth crystals are promising platforms for quantum information, with potentially long coherence times and telecom-compatible optical transitions. In this work, we investigate the optical properties of erbium atoms doped into a whispering gallery mode resonator produced by polishing a yttrium orthosilicate crystal. The multimode resonator demonstrates a bare quality factor of 2.56×10 5 . We demonstrate mode interaction between atoms and the resonator, where an effective quality factor of 8.7×10 7 is induced by spectral hole burning. The Fano interference between the atomic (spectral holes) and optical modes, and the small free-spectral range achieved here, can enable the study of tuning-free linear and nonlinear collective interactions.

Optics Letters•Sep 16, 2026•0 citations
We showcase an erbium-doped whispering-gallery-mode resonator with optical modes that display intrinsic quality factors better than 10810^8108 (linewidths less than 2 MHz), and coupling strengths to collective erbium transitions of up to 2π×π\timesπ×1.2 GHz - enough to reach the ensemble strong coupling regime. Our optical cavity sits inside a microwave resonator, allowing us to probe the spin transition which is tuned by an external magnetic field. We show a modified optically detected magnetic resonance measurement that measures population transfer by a change in coupling strength rather than absorption coefficient. This modification was enabled by the strong coupling to our modes, and allows us to optically probe the spin transition detuned by more than the inhomogeneous linewidth. We contrast this measurement with electron paramagnetic resonance to experimentally show that our optical modes are confined in a region of large microwave magnetic field and we explore how such a geometry could be used for coherent microwave-optical transduction.
We introduce a method for optically detected magnetic resonance for atomlike systems in an optical resonator. Driving the spin transitions of these systems with microwaves causes changes to the populations of the ground-state spin levels, which we detect by changes in the optical cavity frequency. The technique is useful for characterizing experiments aimed at quantum microwave-to-optical transduction because it provides a way of only probing the spin transitions of the atomlike systems that are in the optical resonator's mode. We demonstrate the technique using a cryogenic erbium-doped whispering-gallery-mode resonator inside a microwave resonator. We compare our results with more standard electron paramagnetic resonance to show that our optical modes are confined to a region of large microwave magnetic-field amplitude. Our optical modes have a QQQ factor better than 108{10}^{8}108 making them the highest QQQ-factor resonators studied with cryogenic rare-earth-ion dopants, allowing us to report ensemble strong coupling between the erbium dopants and an optical whispering-gallery-mode resonator.
Erbium-doped crystals provide a promising platform for integration with other quantum systems, offering telecom-band optical and microwave spin transitions with long coherence times for quantum memory and transduction applications. In order to construct efficient hybrid quantum systems, it is challenging but necessary to realize strong coupling between erbium spins and other microwave photons. Here, we design and construct a high-quality-factor three-dimensional loop-gap microwave resonator for wide-range electron spin resonance detection. We achieved strong coupling with a strength of 85.1 MHz at 100 mK. Our results demonstrate a viable hybrid quantum system, paving the way for integrated networks that combine optical communication with microwave quantum computing.
Microwave-to-optical quantum transducers are essential for entangling remote superconducting qubits. Among the available transduction platforms, ensembles of Er3+^{3+}3+ and Yb3+^{3+}3+ ions doped into solids have emerged as leading candidates. While external magnetic fields are needed to split the Zeeman levels of erbium ions and enable a microwave--qubit interface, superconducting qubits suffer decoherence in such fields. In contrast, ytterbium ions exhibit zero-first-order Zeeman transitions and large hyperfine splittings at zero magnetic field (when doped into inorganic crystals). Owing to its long optical and spin coherence times, Yb:YSO has been widely used as a quantum memory, yet its potential for quantum transduction remains largely unexplored. Investigating this material could enable the integration of quantum memory and transduction in a single platform. Here, we demonstrate microwave-to-optical transduction in the continuous-wave regime using a 5\,ppm doped Yb:YSO crystal. The internal transduction efficiency is 2×10−82\times10^{-8}2×10−8 with a bandwidth of 200\,kHz, achieved using a 3D loop-gap microwave resonator (LGR) and a single-pass optical configuration. We explore all the ground states that form a V-type three-level system with the first and second optical excited states and assert the use of the ground state, which provides the highest efficiency and isolated optical transition. We further establish strong spin-microwave coupling from avoided crossing measurements. With a strong microwave drive to saturate the spin transition, we estimate the spin population pumped into the excited state, close to the simulated value. Finally, we calculate target parameter values for maximum efficiency with our system and suggest using 50\,ppm doped Yb:YSO crystal. With the calculated target parameters, the internal transduction efficiency is predicted to reach up to 10−410^{-4}10−4 in the current LGR.
The quantum coupling of spatially distant spins via optical photons using cavity quantum electrodynamic (cQED) methods has proved experimentally challenging due to the large spin-photon coupling strengths required. To achieve such coupling strengths using traditional cQED methods requires either individual spins and ultra-small cavities or an ensemble of identical spins coupled to larger cavities. In this work we describe a method to couple distant spins via the collective enhanced coupling to a large ensemble ∼ N, of degenerate optical Whispering Gallery Modes (WGM) in a spherical resonator where the spins are spatially located at the antipodes. The setup can be scaled-up to build 1D, 2D and 3D cQED lattices to enable quantum simulation or computing.
A quantum coherent interface between optical and microwave photons can be used as a basic building block within a future quantum information network. The interface is envisioned as an ensemble of rare-earth ions coupled to a superconducting resonator, allowing for coherent transfer between optical and microwave photons. Towards this end, we have realized a hybrid device coupling a Er3+-doped Y2SiO5 crystal in a superconducting coplanar waveguide cavity. We observe a collective spin coupling of 4 MHz and a spin linewidth of down to 75 MHz.
Rare-earth crystals are promising platforms for quantum information, with potentially long coherence times and telecom-compatible optical transitions. In this work, we investigate the optical properties of erbium atoms doped into a whispering gallery mode resonator produced by polishing a yttrium orthosilicate crystal. The multimode resonator demonstrates a bare quality factor of 2.56×10 5 . We demonstrate mode interaction between atoms and the resonator, where an effective quality factor of 8.7×10 7 is induced by spectral hole burning. The Fano interference between the atomic (spectral holes) and optical modes, and the small free-spectral range achieved here, can enable the study of tuning-free linear and nonlinear collective interactions.