Fabrication and nanophotonic waveguide integration of silicon carbide colour centres with preserved spin-optical coherence.

Optically addressable spin defects in silicon carbide (SiC) are an emerging platform for quantum information processing compatible with nanofabrication processes and device control used by the semiconductor industry. System scalability towards large-scale quantum networks demands integration into nanophotonic structures with efficient spin-photon interfaces. However, degradation of the spin-optical coherence after integration in nanophotonic structures has hindered the potential of most colour centre platforms. Here, we demonstrate the implantation of silicon vacancy centres (VSi) in SiC without deterioration of their intrinsic spin-optical properties. In particular, we show nearly lifetime-limited photon emission and high spin-coherence times for single defects implanted in bulk as well as in nanophotonic waveguides created by reactive ion etching. Furthermore, we take advantage of the high spin-optical coherences of VSi centres in waveguides to demonstrate controlled operations on nearby nuclear spin qubits, which is a crucial step towards fault-tolerant quantum information distribution based on cavity quantum electrodynamics.

Laser Writing of Scalable Single Color Centers in Silicon Carbide.

Single photon emitters in silicon carbide (SiC) are attracting attention as quantum photonic systems ( Awschalom et al. Nat. Photonics 2018 , 12 , 516 - 527 ; Atatüre et al. Nat. Rev. Mater. 2018 , 3 , 38 - 51 ). However, to achieve scalable devices, it is essential to generate single photon emitters at desired locations on demand. Here we report the controlled creation of single silicon vacancy (VSi) centers in 4H-SiC using laser writing without any postannealing process. Due to the aberration correction in the writing apparatus and the nonannealing process, we generate single VSi centers with yields up to 30%, located within about 80 nm of the desired position in the transverse plane. We also investigated the photophysics of the laser writing VSi centers and concluded that there are about 16 photons involved in the laser writing VSi center process. Our results represent a powerful tool in the fabrication of single VSi centers in SiC for quantum technologies and provide further insights into laser writing defects in dielectric materials.

Growth and characterization of thorium-doped calcium fluoride single crystals.

We have grown [Formula: see text]Th:CaF[Formula: see text] and [Formula: see text]Th:CaF[Formula: see text] single crystals for investigations on the VUV laser-accessible first nuclear excited state of [Formula: see text]Th, with the aim of building a solid-state nuclear clock. To reach high doping concentrations despite the extreme scarcity (and radioactivity) of [Formula: see text]Th, we have scaled down the crystal volume by a factor 100 compared to established commercial or scientific growth processes. We use the vertical gradient freeze method on 3.2 mm diameter seed single crystals with a 2 mm drilled pocket, filled with a co-precipitated CaF[Formula: see text]:ThF[Formula: see text]:PbF[Formula: see text] powder in order to grow single crystals. Concentrations of [Formula: see text] cm[Formula: see text] have been realized with [Formula: see text]Th with good (> 10%) VUV transmission. However, the intrinsic radioactivity of [Formula: see text]Th drives radio-induced dissociation during growth and radiation damage after solidification. Both lead to a degradation of VUV transmission, currently limiting the [Formula: see text]Th concentration to [Formula: see text] cm[Formula: see text].