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Register a new userStark Tuning and Electrical Charge State Control of Single Divacancies in Silicon Carbide
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Neutrally charged divacancies in silicon carbide (SiC) are paramagnetic color centers whose long coherence times and near-telecom operating wavelengths make them promising for scalable quantum communication technologies compatible with existing fiber optic networks. However, local strain inhomogeneity can randomly perturb their optical transition frequencies, which degrades the indistinguishability of photons emitted from separate defects, and hinders their coupling to optical cavities. Here we show that electric fields can be used to tune the optical transition frequencies of single neutral divacancy defects in 4H-SiC over a range of several GHz via the DC Stark effect. The same technique can also control the charge state of the defect on microsecond timescales, which we use to stabilize unstable or non-neutral divacancies into their neutral charge state. Using fluorescence-based charge state detection, we show both 975 nm and 1130 nm excitation can prepare its neutral charge state with near unity efficiency.
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Silicon carbide has recently been developed as a platform for optically addressable spin defects. In particular, the neutral divacancy in the 4H polytype displays an optically addressable spin-1 ground state and near-infrared optical emission. Here, we present the Purcell enhancement of a single neutral divacancy coupled to a photonic crystal cavity. We utilize a combination of nanolithographic techniques and a dopant-selective photoelectrochemical etch to produce suspended cavities with quality factors exceeding 5,000. Subsequent coupling to a single divacancy leads to a Purcell factor of ~50, which manifests as increased photoluminescence into the zero-phonon line and a shortened excited-state lifetime. Additionally, we measure coherent control of the divacancy ground state spin inside the cavity nanostructure and demonstrate extended coherence through dynamical decoupling. This spin-cavity system represents an advance towards scalable long-distance entanglement protocols using silicon carbide that require the interference of indistinguishable photons from spatially separated single qubits.
Transition metal ions provide a rich set of optically active defect spins in wide bandgap semiconductors. Chromium (Cr4+) in silicon-carbide (SiC) produces a spin-1 ground state with a narrow, spectrally isolated, spin-selective, near-telecom optical interface. However, previous studies were hindered by material quality resulting in limited coherent control. In this work, we implant Cr into commercial 4H-SiC and show optimal defect activation after annealing above 1600 C. We measure an ensemble optical hole linewidth of 31 MHz, an order of magnitude improvement compared to as-grown samples. An in-depth exploration of optical and spin dynamics reveals efficient spin polarization, coherent control, and readout with high fidelity (79%). We report T1 times greater than 1 second at cryogenic temperatures (15 K) with a T2* = 317 nanoseconds and a T2 = 81 microseconds, where spin dephasing times are currently limited by spin-spin interactions within the defect ensemble. Our results demonstrate the potential of Cr4+ in SiC as an extrinsic, optically active spin qubit.
Spin defects in silicon carbide have exceptional electron spin coherence with a near-infrared spin-photon interface in a material amenable to modern semiconductor fabrication. Leveraging these advantages, we successfully integrate highly coherent single neutral divacancy spins in commercially available p-i-n structures and fabricate diodes to modulate the local electrical environment of the defects. These devices enable deterministic charge state control and broad Stark shift tuning exceeding 850 GHz. Surprisingly, we show that charge depletion results in a narrowing of the optical linewidths by over 50 fold, approaching the lifetime limit. These results demonstrate a method for mitigating the ubiquitous problem of spectral diffusion in solid-state emitters by engineering the electrical environment while utilizing classical semiconductor devices to control scalable spin-based quantum systems.
Optically interfaced spins in the solid promise scalable quantum networks. Robust and reliable optical properties have so far been restricted to systems with inversion symmetry. Here, we release this stringent constraint by demonstrating outstanding optical and spin properties of single silicon vacancy centres in silicon carbide. Despite the lack of inversion symmetry, the systems particular wave function symmetry decouples its optical properties from magnetic and electric fields, as well as from local strain. This provides a high-fidelity spin-to-photon interface with exceptionally stable and narrow optical transitions, low inhomogeneous broadening, and a large fraction of resonantly emitted photons. Further, the weak spin-phonon coupling results in electron spin coherence times comparable with nitrogen-vacancy centres in diamond. This allows us to demonstrate coherent hyperfine coupling to single nuclear spins, which can be exploited as qubit memories. Our findings promise quantum network applications using integrated semiconductor-based spin-to-photon interfaces.
We study the optical properties of tetravalent vanadium impurities in 4H silicon carbide (4H SiC). Emission from two crystalline sites is observed at wavelengths of 1.28 mum and 1.33 mum, with optical lifetimes of 163 ns and 43 ns. Group theory and ab initio density functional supercell calculations enable unequivocal site assignment and shed light on the spectral features of the defects. We conclude with a brief outlook on applications in quantum photonics.
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