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arXiv:2608.04797

High-cooperativity coupling and spin-resolved extinction of tin-vacancy centers in a diamond-like microcavity

Kerim Köster, András Laukó, Federico Rapisarda, Philipp Graßhoff, Vladislav Bushmakin, Jens Fuhrmann, Ou Wang, Dominic Reinhardt, Doğuşcan Ahiboz, Peter Knittel, Thomas Hümmer, Wolfgang Wernsdorfer, Jörg Wrachtrup, Fedor Jelezko, Tommaso Pregnolato, Tim Schröder, Jan Meijer, Cyril Popov, David Hunger

quant-phSubmitted Aug 5, 2026• Announced Aug 6, 2026• 0 citations
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Abstract

The tin-vacancy (SnV) center in diamond is a promising spin-photon interface for quantum networks, combining favorable optical properties with spin coherence above 1K. Unfolding the full potential requires cavity enhancement to increase photon-emitter coupling efficiency. Here, we demonstrate cavity-enhanced light-matter coupling of SnV centers in a fully tunable Fabry-Pérot microcavity operating at temperatures down to 1K with in-situ magnetic field control. We access the diamond-like regime of hybrid cavity modes through integration of low-roughness diamond membranes, where the field is concentrated inside the diamond and Purcell enhancement is maximized. Diamond-like modes deliver a more than two-fold increase in the effective Purcell factor over air-like modes, reaching $C_0 = 4.1(1)$ compared to $C_0 = 1.85(5)$ in the air-like case, while simultaneously relaxing mechanical stability requirements. Resonant probing reveals coherent cavity-emitter coupling with 96% extinction contrast and a coherent cooperativity of $C = 4.0(14)$. By applying a magnetic field, we further achieve spin-resolved cavity extinction, observing spin-selective optical transitions with a contrast of ${\cal C}_{\rm spin} = 0.91$. These results establish SnV centers in diamond coupled to open Fabry-Pérot microcavities as a promising platform for efficient spin-photon interfaces.

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The tin-vacancy (SnV) center in diamond is a promising spin-photon interface for quantum networks, combining favorable optical properties with spin coherence above 1K. Unfolding the full potential requires cavity enhancement to increase photon-emitter coupling efficiency. Here, we demonstrate cavity-enhanced light-matter coupling of SnV centers in a fully tunable Fabry-Pérot microcavity operating at temperatures down to 1K with in-situ magnetic field control. We access the diamond-like regime of hybrid cavity modes through integration of low-roughness diamond membranes, where the field is concentrated inside the diamond and Purcell enhancement is maximized. Diamond-like modes deliver a more than two-fold increase in the effective Purcell factor over air-like modes, reaching C0=4.1(1)C_0 = 4.1(1)C0​=4.1(1) compared to C0=1.85(5)C_0 = 1.85(5)C0​=1.85(5) in the air-like case, while simultaneously relaxing mechanical stability requirements. Resonant probing reveals coherent cavity-emitter coupling with 96% extinction contrast and a coherent cooperativity of C=4.0(14)C = 4.0(14)C=4.0(14). By applying a magnetic field, we further achieve spin-resolved cavity extinction, observing spin-selective optical transitions with a contrast of Cspin=0.91{\cal C}_{\rm spin} = 0.91Cspin​=0.91. These results establish SnV centers in diamond coupled to open Fabry-Pérot microcavities as a promising platform for efficient spin-photon interfaces.
The realization of quantum networks critically depends on establishing efficient, coherent light-matter interfaces. Optically active spins in diamond have emerged as promising quantum nodes based on their spin-selective optical transitions, long-lived spin ground states, and potential for integration with nanophotonics. Tin-vacancy (SnV -^{\,\textrm{-}}-) centers in diamond are of particular interest because they exhibit narrow-linewidth emission in nanostructures and possess long spin coherence times at temperatures above 1 K. However, a nanophotonic interface for SnV -^{\,\textrm{-}}- centers has not yet been realized. Here, we report cavity enhancement of the emission of SnV -^{\,\textrm{-}}- centers in diamond. We integrate SnV -^{\,\textrm{-}}- centers into one-dimensional photonic crystal resonators and observe a 40-fold increase in emission intensity. The Purcell factor of the coupled system is 25, resulting in channeling of the majority of photons (90%90\%90%) into the cavity mode. Our results pave the way for the creation of efficient, scalable spin-photon interfaces based on SnV -^{\,\textrm{-}}- centers in diamond.
The tin-vacancy center in diamond (SnV) has emerged as a compelling building block for realizing next-generation quantum networks thanks to its excellent optical and spin properties. Coupling to photonic crystal cavities (PCCs) promises to further enhance the SnV light-matter interface and unlock a diverse range of entanglement generation protocols. Recent pioneering experiments showing Purcell enhancement of SnV centers in PCCs underscore this potential. However, optical coupling that is coherent - the key ingredient for use in quantum protocols - has so far remained elusive. Here, we demonstrate above-unity coherent cooperativity of SnV centers embedded in photonic crystal cavities. We fabricate free-standing PCCs using a quasi-isotropic undercut. Across two samples, we conduct room-temperature characterizations, measuring resonances for 327 cavities, with an average quality factor exceeding Q=1.0(3)×104Q = 1.0(3) \times 10^4Q=1.0(3)×104. Two cavity-coupled emitters are examined in detail, exhibiting quality factors up to Q=25.4(4)×103Q = 25.4(4) \times 10^3Q=25.4(4)×103 and Purcell-reduced lifetimes corresponding to cooperativities up to C=20.6(11)C = 20.6(11)C=20.6(11). Furthermore, the single SnVs are observed to strongly modulate the cavity transmission with an extinction contrast up to 98.8(4)%98.8(4) \%98.8(4)% on resonance. Finally, SnV linewidth measurements reveal above-unity coherent cooperativities in both devices, with the highest value being Ccoh=8.3(12)C_\mathrm{coh} = 8.3(12)Ccoh​=8.3(12). These results open the door to using cavity-coupled SnV centers as efficient, coherent light-matter interfaces for future quantum networks.
Efficient coupling between quantum emitters and optical cavities is essential for scalable quantum photonic technologies. Group-IV vacancy centers in diamond, particularly the negatively charged tin-vacancy center, have emerged as promising candidates due to their spectral stability, high Debye-Waller factor, and large orbital splitting in ground states. Here, we demonstrate controlled coupling of a single negatively charged tin-vacancy center hosted in a nanodiamond to a fully tunable Fabry-Pérot microcavity. At cryogenic temperatures, we access the weak-coupling regime and observe a transition from the bad-emitter regime to the bad-cavity regime as the optical transition of the color center narrows. At 4 K, a Purcell factor exceeding 1.7 is measured, confirming cavity-enhanced emission. The obtained results demonstrate the potential of Sn − V − centers in nanodiamonds as a coherent single-photon source for quantum networks.
Efficient coupling of optically active qubits to optical cavities is a key challenge for solid-state-based quantum optics experiments and future quantum technologies. Here we present a quantum photonic interface based on a single tin-vacancy center in a micrometer-thin diamond membrane coupled to a tunable open microcavity. We use the full tunability of the microcavity to selectively address individual tin-vacancy centers within the cavity mode volume. Purcell enhancement of the tin-vacancy center optical transition is evidenced both by optical excited state lifetime reduction and by optical linewidth broadening. As the emitter selectively reflects the single-photon component of the incident light, the coupled emitter-cavity system exhibits strong quantum nonlinear behavior. On resonance, we observe a transmission dip of 50% for low incident photon number per Purcell-reduced excited state lifetime, while the dip disappears as the emitter is saturated with higher photon number. Moreover, we demonstrate that the emitter strongly modifies the photon statistics of the transmitted light by observing photon bunching. This work establishes a versatile and tunable platform for advanced quantum optics experiments and proof-of-principle demonstrations on quantum networking with solid-state qubits. Published by the American Physical Society 2024
Quantum networks rely on the efficient coupling of coherent quantum memories to photonic links. Tin-vacancy centers (SnV) have emerged as promising candidates for the implementation of an optically interfaced quantum memory based on their long spin coherence times at temperatures above 1K. To enhance their interaction with photons SnV centers need to be integrated with high-quality photonic structures. In this work, we report the enhancement of coherent emission of SnV centers by coupling them to a nanophotonic waveguide resonator. We observe strong intensity enhancement of the photon emission when the cavity is resonant with the color center. We demonstrate strong enhancement of the radiative recombination rate of SnV centers resulting in their predominant emission via the coherent zero-phonon line and into the cavity mode. These results are a significant step toward color-center-based quantum information processing applications without the need for dilution refrigerators.
Efficient optical interfacing of spin-bearing quantum emitters is a crucial ingredient for quantum networks. A promising route therefore is to incorporate host materials as minimally processed membranes into open-access microcavities: it enables significant emission enhancement and efficient photon collection, minimizes deteriorating influence on the quantum emitter, and allows for full spatial and spectral tunability. Here, we study the properties of a high-finesse fiber Fabry-P\'erot microcavity with integrated single-crystal diamond membranes by scanning cavity microscopy. We observe the spatially resolved effects of the diamond-air interface on the cavity-mode structure: a strong correlation of the cavity finesse and mode structure with the diamond thickness and surface topography, prevalent transverse-mode mixing under diamondlike conditions, and mode-character-dependent polarization-mode splitting. Our results reveal the influence of the diamond surface on the achievable Purcell enhancement, which helps to clarify the route towards optimized spin-photon interfaces.