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Spin-active quantum emitters have emerged as a leading platform for quantum technologies. However, one of their major limitations is the large spread in optical emission frequencies, which typically extends over tens of GHz. Here, we investigate single V4+ vanadium centres in 4H-SiC, which feature telecom-wavelength emission and a coherent S = 1/2 spin state. We perform spectroscopy on single emitters and report the observation of spin-dependent optical transitions, a key requirement for spin-photon interfaces. By engineering the isotopic composition of the SiC matrix, we reduce the inhomogeneous spectral distribution of different emitters down to 100 MHz, significantly smaller than any other single quantum emitter. Additionally, we tailor the dopant concentration to stabilise the telecom-wavelength V4+ charge state, thereby extending its lifetime by at least two orders of magnitude. These results bolster the prospects for single V emitters in SiC as material nodes in scalable telecom quantum networks. Several solid-state defect platforms have been proposed for application as a spin-photon interface in quantum communication networks. Here the authors report spin-selective optical transitions and narrow inhomogeneous spectral distribution of V centers in isotopically-enriched SiC emitting in the telecom O-band., Funding Agencies|European Commission project QuanTELCO [862721]; Engineering and Physical Sciences Research Council [EP/S000550/1]; Leverhulme Trust [RPG-2019-388]; Austrian Research Promotion Agency [QSense4Power (FFG 877615)]; Swedish Research Council [VR:2020-05444]; Knut and Alice Wallenberg Foundation [KAW 2018.0071]

Scalable quantum networking requires quantum systems with quantum processing capabilities. Solid state spin systems with reliable spin-optical interfaces are a leading hardware in this regard. However, available systems suffer from large electron-phonon interaction or fast spin dephasing. Here, we demonstrate that the negatively charged silicon-vacancy centre in silicon carbide is immune to both drawbacks. Thanks to its (4)A(2) symmetry in ground and excited states, optical resonances are stable with near-Fourier-transform-limited linewidths, allowing exploitation of the spin selectivity of the optical transitions. In combination with millisecond-long spin coherence times originating from the high-purity crystal, we demonstrate high-fidelity optical initialization and coherent spin control, which we exploit to show coherent coupling to single nuclear spins with similar to 1 kHz resolution. The summary of our findings makes this defect a prime candidate for realising memory-assisted quantum network applications using semiconductor-based spin-to-photon interfaces and coherently coupled nuclear spins., Funding Agencies|Carl-Zeiss-Stiftung; European Research Council (ERC) grant SMel; European Commission Marie Curie ETN "QuSCo" [765267]; Max Planck Society; Humboldt Foundation; German Science Foundation [SPP 1601]; KIST institutional program [2E29580]; EPSRC [EP/P019803/1]; Royal Society; Swedish Research Council [VR 2016-04068, VR 2016-05362]; Carl Trygger Stiftelse for Vetenskaplig Forskning [CTS 15: 339]; Knut and Alice Wallenberg Foundation [KAW 2018.0071]; Swedish Energy Agency [43611-1]; JSPS KAKENHI [17H01056]; Hungarian NKFIH of the EU QuantERA Nanospin project [NN118161]; National Quantum Technology Program [2017-1.2.1-NKP-2017-00001]

Scalable quantum networking requires quantum systems with quantum processing capabilities. Solid state spin systems with reliable spin-optical interfaces are a leading hardware in this regard. However, available systems suffer from large electron-phonon interaction or fast spin dephasing. Here, we demonstrate that the negatively charged silicon-vacancy centre in silicon carbide is immune to both drawbacks. Thanks to its (4)A(2) symmetry in ground and excited states, optical resonances are stable with near-Fourier-transform-limited linewidths, allowing exploitation of the spin selectivity of the optical transitions. In combination with millisecond-long spin coherence times originating from the high-purity crystal, we demonstrate high-fidelity optical initialization and coherent spin control, which we exploit to show coherent coupling to single nuclear spins with similar to 1 kHz resolution. The summary of our findings makes this defect a prime candidate for realising memory-assisted quantum network applications using semiconductor-based spin-to-photon interfaces and coherently coupled nuclear spins., Funding Agencies|Carl-Zeiss-Stiftung; European Research Council (ERC) grant SMel; European Commission Marie Curie ETN "QuSCo" [765267]; Max Planck Society; Humboldt Foundation; German Science Foundation [SPP 1601]; KIST institutional program [2E29580]; EPSRC [EP/P019803/1]; Royal Society; Swedish Research Council [VR 2016-04068, VR 2016-05362]; Carl Trygger Stiftelse for Vetenskaplig Forskning [CTS 15: 339]; Knut and Alice Wallenberg Foundation [KAW 2018.0071]; Swedish Energy Agency [43611-1]; JSPS KAKENHI [17H01056]; Hungarian NKFIH of the EU QuantERA Nanospin project [NN118161]; National Quantum Technology Program [2017-1.2.1-NKP-2017-00001]

Scalable quantum networking requires quantum systems with quantum processing capabilities. Solid state spin systems with reliable spin-optical interfaces are a leading hardware in this regard. However, available systems suffer from large electron-phonon interaction or fast spin dephasing. Here, we demonstrate that the negatively charged silicon-vacancy centre in silicon carbide is immune to both drawbacks. Thanks to its (4)A(2) symmetry in ground and excited states, optical resonances are stable with near-Fourier-transform-limited linewidths, allowing exploitation of the spin selectivity of the optical transitions. In combination with millisecond-long spin coherence times originating from the high-purity crystal, we demonstrate high-fidelity optical initialization and coherent spin control, which we exploit to show coherent coupling to single nuclear spins with similar to 1 kHz resolution. The summary of our findings makes this defect a prime candidate for realising memory-assisted quantum network applications using semiconductor-based spin-to-photon interfaces and coherently coupled nuclear spins., Funding Agencies|Carl-Zeiss-Stiftung; European Research Council (ERC) grant SMel; European Commission Marie Curie ETN "QuSCo" [765267]; Max Planck Society; Humboldt Foundation; German Science Foundation [SPP 1601]; KIST institutional program [2E29580]; EPSRC [EP/P019803/1]; Royal Society; Swedish Research Council [VR 2016-04068, VR 2016-05362]; Carl Trygger Stiftelse for Vetenskaplig Forskning [CTS 15: 339]; Knut and Alice Wallenberg Foundation [KAW 2018.0071]; Swedish Energy Agency [43611-1]; JSPS KAKENHI [17H01056]; Hungarian NKFIH of the EU QuantERA Nanospin project [NN118161]; National Quantum Technology Program [2017-1.2.1-NKP-2017-00001]

Scalable quantum networking requires quantum systems with quantum processing capabilities. Solid state spin systems with reliable spin-optical interfaces are a leading hardware in this regard. However, available systems suffer from large electron-phonon interaction or fast spin dephasing. Here, we demonstrate that the negatively charged silicon-vacancy centre in silicon carbide is immune to both drawbacks. Thanks to its (4)A(2) symmetry in ground and excited states, optical resonances are stable with near-Fourier-transform-limited linewidths, allowing exploitation of the spin selectivity of the optical transitions. In combination with millisecond-long spin coherence times originating from the high-purity crystal, we demonstrate high-fidelity optical initialization and coherent spin control, which we exploit to show coherent coupling to single nuclear spins with similar to 1 kHz resolution. The summary of our findings makes this defect a prime candidate for realising memory-assisted quantum network applications using semiconductor-based spin-to-photon interfaces and coherently coupled nuclear spins., Funding Agencies|Carl-Zeiss-Stiftung; European Research Council (ERC) grant SMel; European Commission Marie Curie ETN "QuSCo" [765267]; Max Planck Society; Humboldt Foundation; German Science Foundation [SPP 1601]; KIST institutional program [2E29580]; EPSRC [EP/P019803/1]; Royal Society; Swedish Research Council [VR 2016-04068, VR 2016-05362]; Carl Trygger Stiftelse for Vetenskaplig Forskning [CTS 15: 339]; Knut and Alice Wallenberg Foundation [KAW 2018.0071]; Swedish Energy Agency [43611-1]; JSPS KAKENHI [17H01056]; Hungarian NKFIH of the EU QuantERA Nanospin project [NN118161]; National Quantum Technology Program [2017-1.2.1-NKP-2017-00001]

Scalable quantum networking requires quantum systems with quantum processing capabilities. Solid state spin systems with reliable spin-optical interfaces are a leading hardware in this regard. However, available systems suffer from large electron-phonon interaction or fast spin dephasing. Here, we demonstrate that the negatively charged silicon-vacancy centre in silicon carbide is immune to both drawbacks. Thanks to its (4)A(2) symmetry in ground and excited states, optical resonances are stable with near-Fourier-transform-limited linewidths, allowing exploitation of the spin selectivity of the optical transitions. In combination with millisecond-long spin coherence times originating from the high-purity crystal, we demonstrate high-fidelity optical initialization and coherent spin control, which we exploit to show coherent coupling to single nuclear spins with similar to 1 kHz resolution. The summary of our findings makes this defect a prime candidate for realising memory-assisted quantum network applications using semiconductor-based spin-to-photon interfaces and coherently coupled nuclear spins., Funding Agencies|Carl-Zeiss-Stiftung; European Research Council (ERC) grant SMel; European Commission Marie Curie ETN "QuSCo" [765267]; Max Planck Society; Humboldt Foundation; German Science Foundation [SPP 1601]; KIST institutional program [2E29580]; EPSRC [EP/P019803/1]; Royal Society; Swedish Research Council [VR 2016-04068, VR 2016-05362]; Carl Trygger Stiftelse for Vetenskaplig Forskning [CTS 15: 339]; Knut and Alice Wallenberg Foundation [KAW 2018.0071]; Swedish Energy Agency [43611-1]; JSPS KAKENHI [17H01056]; Hungarian NKFIH of the EU QuantERA Nanospin project [NN118161]; National Quantum Technology Program [2017-1.2.1-NKP-2017-00001]

Color centers with long-lived spins are established platforms for quantum sensing and quantum information applications. Color centers exist in different charge states, each of them with distinct optical and spin properties. Application to quantum technology requires the capability to access and stabilize charge states for each specific task. Here, we investigate charge state manipulation of individual silicon vacancies in silicon carbide, a system which has recently shown a unique combination of long spin coherence time and ultrastable spin-selective optical transitions. In particular, we demonstrate charge state switching through the bias applied to the color center in an integrated silicon carbide optoelectronic device. We show that the electronic environment defined by the doping profile and the distribution of other defects in the device plays a key role for charge state control. Our experimental results and numerical modeling evidence that control of these complex interactions can, under certain conditions, enhance the photon emission rate. These findings open the way for deterministic control over the charge state of spin-active color centers for quantum technology and provide novel techniques for monitoring doping profiles and voltage sensing in microscopic devices., Funding Agencies|Ministry of Education and Science of the Russian FederationMinistry of Education and Science, Russian Federation [8.9898.2017/6.7]; Russian Foundation for Basic ResearchRussian Foundation for Basic Research (RFBR) [19-57-12008]; Russian FederationRussian Federation [MK-2602.2017.9]; Baden-Wurttemberg Stiftung Programm: Internationale Spitzenforschung; ERC SMel; BMBF BRAINQSENSFederal Ministry of Education & Research (BMBF); Korea Institute of Science and Technology institutional program [2E29580, 2E27110]; Swedish Research CouncilSwedish Research Council [VR 2016-04068, VR 201605362]; Carl Tryggers Stiftelse for Vetenskaplig Forskning [CTS 15:339]; Swedish Energy AgencySwedish Energy Agency [43611-1]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation [KAW 2018.0071]; National Quantum Technology Program from the National Office of Research, Development and Innovation in Hungary [2017-1.2.1-NKP-2017-00001]; National Excellence Program from the National Office of Research, Development and Innovation in Hungary [KKP129866]; EU QuantERA Nanospin project from the National Office of Research, Development and Innovation in Hungary [127902]; Engineering and Physical Sciences Research CouncilEngineering & Physical Sciences Research Council (EPSRC) [EP/P019803/1, EP/S000550/1]; Networked Quantum Information Technologies Hub (Oxford); JSPS KAKENHIMinistry of Education, Culture, Sports, Science and Technology, Japan (MEXT)Japan Society for the Promotion of ScienceGrants-in-Aid for Scientific Research (KAKENHI) [17H01056, 18H03770]; Carnegie Trust for Scotland [RIG007503]

Scalable quantum networking requires quantum systems with quantum processing capabilities. Solid state spin systems with reliable spin-optical interfaces are a leading hardware in this regard. However, available systems suffer from large electron-phonon interaction or fast spin dephasing. Here, we demonstrate that the negatively charged silicon-vacancy centre in silicon carbide is immune to both drawbacks. Thanks to its (4)A(2) symmetry in ground and excited states, optical resonances are stable with near-Fourier-transform-limited linewidths, allowing exploitation of the spin selectivity of the optical transitions. In combination with millisecond-long spin coherence times originating from the high-purity crystal, we demonstrate high-fidelity optical initialization and coherent spin control, which we exploit to show coherent coupling to single nuclear spins with similar to 1 kHz resolution. The summary of our findings makes this defect a prime candidate for realising memory-assisted quantum network applications using semiconductor-based spin-to-photon interfaces and coherently coupled nuclear spins., Funding Agencies|Carl-Zeiss-Stiftung; European Research Council (ERC) grant SMel; European Commission Marie Curie ETN "QuSCo" [765267]; Max Planck Society; Humboldt Foundation; German Science Foundation [SPP 1601]; KIST institutional program [2E29580]; EPSRC [EP/P019803/1]; Royal Society; Swedish Research Council [VR 2016-04068, VR 2016-05362]; Carl Trygger Stiftelse for Vetenskaplig Forskning [CTS 15: 339]; Knut and Alice Wallenberg Foundation [KAW 2018.0071]; Swedish Energy Agency [43611-1]; JSPS KAKENHI [17H01056]; Hungarian NKFIH of the EU QuantERA Nanospin project [NN118161]; National Quantum Technology Program [2017-1.2.1-NKP-2017-00001]

Although various defect centers have displayed promise as either quantum sensors, single photon emitters, or light-matter interfaces, the search for an ideal defect with multifunctional ability remains open. In this spirit, we study the dichroic silicon vacancies in silicon carbide that feature two well-distinguishable zero-phonon lines and analyze the quantum properties in their optical emission and spin control. We demonstrate that this center combines 40% optical emission into the zero-phonon lines showing the contrasting difference in optical properties with varying temperature and polarization, and a 100% increase in the fluorescence intensity upon the spin resonance, and long spin coherence time of their spin-3/2 ground states up to 0.6 ms. These results single out this defect center as a promising system for spin-based quantum technologies.