Quantum information processing (QIP) is among the most rapidly developing areas of science and technology. It is perhaps the final frontier in the quest to harness the fundamental properties of matter for computation, com-munication, data processing, and molecular simulation.
Any physical system governed by the laws of quantum mechanics can in principle be a candidate for QIP; to date, however, the most advanced QIP demonstrations have been implemented via superconducting qubits [1], trapped ions and atoms [2,3], and photons (via linear-optical quantum computing) [4]. Recently, optically addressable crystal defects have emerged as a novel platform for QIP [5– 8], interfacing some of nature’s best quantum memories (a protected solid-state spin [9–11]) with a robust flying qubit (photon) that can transport the quantum informa- tion [12]. Notably, solid-state defects lend themselves to on-chip integration, promising future scalability. Optically addressable spin defects are thus noteworthy candidates for several QIP proposals, including network-based quantum computing [13–15], cluster state generation [16–18], and quantum communications [19,20].
Optically addressable solid-state spin defects are promising candidates for storing and manipulating quantum information using their long coherence ground-state manifold; individual defects can be entan- gled using photon-photon interactions, offering a path toward large-scale quantum photonic networks. Quantum computing protocols place strict limits on the acceptable photon losses in the system. These low- loss requirements cannot be achieved without photonic engineering, but are attainable if combined with state-of-the-art nanophotonic technologies. However, most materials that host spin defects are challenging to process: as a result, the performance of quantum photonic devices is orders of magnitude behind that of their classical counterparts. Silicon carbide (SiC) is well suited to bridge the classical-quantum photonics gap, since it hosts promising optically addressable spin defects and can be processed into SiC-on-insulator for scalable, integrated photonics. In this paper, we discuss recent progress toward the development of scalable quantum photonic technologies based on solid-state spins in silicon carbide, and discuss current challenges and future directions.
In summary, spin-based photonic technologies for quan- tum computing will likely operate in the network architec- ture (Fig. 1) and will require the integration of spin-qubit registers with high-quality photonic structures and efficient photon detectors to reduce the total photon loss below the demanding thresholds for quantum computing [15]. While there may be numerous approaches for achieving this goal, we believe that a fully chip-integrated quantum photonic platform holds the most promise, as this approach is most scalable and avoids additional coupling loss from waveguide interconnects. SiC has emerged as a promising platform for realizing this technology, with demonstrations of wafer-scale integration of high-quality emitters into semiconductor junctions [63], isotopic engineering for nuclear spin registers [88], indistinguishable single-photon emission [52], and a quantum-grade SiC-on-insulator plat- form for fabrication of photonic devices [32]. However, several key results must be demonstrated to confirm its promise, starting with the integration of large arrays of tunable narrow-linewidth emitters into nanostructures.
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