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arXiv:2507.06553 · Physical Review Applied

Tunable cavity coupling of a single Sn - V − center in nanodiamond across the bad-emitter and bad-cavity regimes

Selene Sachero, Robert Berghaus, Florian Feuchtmayr, Niklas Lettner, Patrick J. Maier, Elena Nieto Hernández, Sviatoslav Ditalia Tchernij, Alexander Kubanek

Published Nov 20, 2025• 0 citations
arXivHTMLPDF

Abstract

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.

DOI
10.1103/8yqs-wtp2

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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.
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 nitrogen vacancy center in diamond in its negative charge state is a promising candidate for quantum optic experiments that require single photon emitters. Important benefits of the NV center are its high brightness and photo-stability, even at room temperature. Engineering the emission properties of NV centers with optical resonators is a widely followed approach to meet the requirements for quantum technological applications, but the effect on non-radiative decay paths is yet to be understood. Here we report on modifying the internal quantum efficiency of a single NV center in a nanodiamond coupled to a 1D photonic crystal cavity. We assess the Purcell enhancement via three independent measurement techniques and perform autocorrelation measurements at elevated excitation powers in confocal microscopy. Employing a three-level model allows us to extract the setup efficiency, individual transition rates and thus the internal quantum efficiency of our system. Combining our results, we find that the enhancement of the radiative decay rate via the Purcell effect results in an internal quantum efficiency of 90 % for cavity-coupled NV centers. Our findings will facilitate the realization of nano-scale single photon sources with near-unity internal quantum efficiencies operating at high repetition rates.
The Nitrogen-Vacancy (NV) centre in diamond possesses an optical read out of its spin state and shows great promise for applications in solid state quantum technologies. Its broad phonon assisted emission spectrum, with only 4% of emission from the zero-phonon line, is a major drawback to this. The optical microcavity will be essential in efficiently interfacing these centres with photonic networks. Here we present investigations into the coupling of NV centres in nanodiamond to tunable open-microcavities, both at room temperature and at cryogenic temperatures. These structures will be shown to achieve good photon confinement, with mode volumes down to 5λ3. Room temperature studies on ensembles of NVs will illustrate the tunable spectral and spatial overlap between the emitter and the cavity mode. It will be shown that small enhancements are possible in this regime. After the preparation and characterisation of single emitters, low temperature coupling to the narrowed zero-phonon line will be the central theme of this thesis. Single photon emission into the cavity mode is verified. We observe the enhancement of the light-matter interaction in this regime, by a 39% increase in the emission rate when cavity-coupled, with the dependence on mode volume also demonstrated. These results are important for the realisation of a spin-photon interface in scalable quantum networks.
We employ a fiber-based optical microcavity with high finesse to study the enhancement of phonon sideband fluorescence of nitrogen-vacancy centers in nanodiamonds. Harnessing the full tunability and open access of the resonator, we explicitly demonstrate the scaling laws of the Purcell enhancement by varying both the mode volume and the quality factor over a large range. While changes in the emission lifetime remain small in the regime of a broadband emitter, we observe an increase of the emission spectral density by up to a factor of 300. This gives a direct measure of the Purcell factor that could be achieved with this resonator and an emitter whose linewidth is narrower than the cavity linewidth. Our results show a method for the realization of wavelength-tunable narrow-band single-photon sources and demonstrate a system that has the potential to reach the strong-coupling regime.
The Nitrogen-Vacancy (NV) centre in diamond possesses an optical read out of its spin state and shows great promise for applications in solid state quantum technologies. Its broad phonon assisted emission spectrum, with only 4p of emission from the zero-phonon line, is a major drawback to this. The optical microcavity will be essential in efficiently interfacing these centres with photonic networks. Here we present investigations into the coupling of NV centres in nanodiamond to tunable open-microcavities, both at room temperature and at cryogenic temperatures. These structures will be shown to achieve good photon confinement, with mode volumes down to 5λ3. Room temperature studies on ensembles of NVs will illustrate the tunable spectral and spatial overlap between the emitter and the cavity mode. It will be shown that small enhancements are possible in this regime. After the preparation and characterisation of single emitters, low temperature coupling to the narrowed zero-phonon line will be the central theme of this thesis. Single photon emission into the cavity mode is verified. We observe the enhancement of the light-matter interaction in this regime, by a 39p increase in the emission rate when cavity-coupled, with the dependence on mode volume also demonstrated. These results are important for the realisation of a spin-photon interface in scalable quantum networks.
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.