ABSTRACT In the rapidly evolving field of quantum technology, the precise and detailed description of quantum components is not just a necessity but the foundation for advancing research, development, and applications. Optically accessible quantum memories are key building blocks for devices such as quantum repeaters and two‐factor authentication. The memory we describe here is based on a Group‐IV‐vacancy color center () coupled to a highly efficient cavity. It leverages state‐dependent reflection from the cavity and implements high‐fidelity fractional single qubit gates via a train of optical pulses. We also describe its operation under microwave control, further extending our analysis. Our primary contribution in this work is the integration of this device model into a standardized software framework for quantum memory architectures.
ABSTRACT In the rapidly evolving field of quantum technology, the precise and detailed description of quantum components is not just a necessity but the foundation for advancing research, development, and applications. Optically accessible quantum memories are key building blocks for devices such as quantum repeaters and two‐factor authentication. The memory we describe here is based on a Group‐IV‐vacancy color center () coupled to a highly efficient cavity. It leverages state‐dependent reflection from the cavity and implements high‐fidelity fractional single qubit gates via a train of optical pulses. We also describe its operation under microwave control, further extending our analysis. Our primary contribution in this work is the integration of this device model into a standardized software framework for quantum memory architectures.
Abstract Diamond has emerged as a highly promising platform for quantum network applications. Color centers in diamond fulfill the fundamental requirements for quantum nodes: they constitute optically accessible quantum systems with long‐lived spin qubits. Furthermore, they provide access to a quantum register of electronic and nuclear spin qubits and they mediate entanglement between spins and photons. All these operations require coherent control of the color center's spin state. This review provides a comprehensive overview of the state‐of‐the‐art, challenges, and prospects of such schemes, including high‐fidelity initialization, coherent manipulation, and readout of spin states. Established microwave and optical control techniques are reviewed, and moreover, emerging methods such as cavity‐mediated spin–photon interactions and mechanical control based on spin–phonon interactions are summarized. For different types of color centers, namely, nitrogen–vacancy and group‐IV color centers, distinct challenges persist that are subject of ongoing research. Beyond fundamental coherent spin qubit control techniques, advanced demonstrations in quantum network applications are outlined, for example, the integration of individual color centers for accessing (nuclear) multiqubit registers. Finally, the role of diamond spin qubits in the realization of future quantum information applications is described.
We propose and analyze a hybrid quantum repeater architecture that combines two leading hardware platforms: quantum dots (QDs) as bright, deterministic sources of entangled photon pairs and group-IV-vacancy centers in diamond as efficient, heralded quantum memories. This combination leverages high-rate entanglement generation together with long-lived storage, enabling scalable entanglement distribution over long distances. A key challenge is the large bandwidth mismatch between QD photons and the narrow optical transitions of the memories. We combine a comprehensive model of the spin-photon interface, including full spin-photon coupling dynamics, and explore mitigation strategies such as frequency filtering and optimized magnetic-field orientation. Our results show that with optimized designs, photon-to-memory transfer can be achieved with high efficiency and fidelity, supporting the feasibility of such hybrid systems. Finally, we analyze a full repeater chain using experimentally achievable parameters and find that a network with thousands of memories across several repeater nodes could achieve a secret-key rate of 500 bit/s over 1,000 km, demonstrating the strong potential of this approach for next-generation quantum networks.
Abstract One ultimate goal of quantum information processing is to construct a quantum network for direct sharing of quantum information between distant parties based on stationary qubits for information storage and flying qubits for information transmission. This requires long‐lived quantum memories, efficient light–matter interface, and deterministic quantum gate operations. Among matter qubits, the electron spin of nitrogen vacancy center in diamond is an appealing option for its long coherence time at room temperature, deterministic microwave control, and optical preparation and readout of the qubit. However, its poor optical properties, including weak zero‐phonon‐line emission and large spectral diffusion, limit its potential for large‐scale deployment in quantum nodes. This has motivated the investigation for alternative quantum emitters that combine long‐time memory and coherent optical properties together. The emerging group‐IV split‐vacancy color centers in diamond, such as silicon‐vacancy, germanium‐vacancy, tin‐vacancy, and lead‐vacancy centers, are promising candidates of this ongoing exploration. These quantum emitters simultaneously possess microsecond spin coherence time and optically bright transitions with narrow linewidths. This review reports recent efforts on extending the spin coherence time of these color centers via temperature, strain, and charge control, which paves the road towards constructing solid‐based matter–photon interface for quantum network applications.
ABSTRACT Quantum computing leverages the principles of quantum mechanics to perform computations that are infeasible for classical computers. Color centers, which are point defects in a crystal lattice where vacancies in the lattice and/or an impurity atom replace a host atom, exhibit unique optical, electronic, and nuclear spin properties that make them suitable for quantum information and communication processing as well as for quantum computations with quantum memory. Among the color centers, nitrogen‐vacancy centers in diamond, the most developed, silicon vacancy (V Si ) centers in silicon carbide (SiC), and boron vacancy (V B ) centers in hexagonal boron nitride (hBN) have emerged as leading candidates. Diamond and SiC material hosts are particularly promising due to the long spin and photon coherence times, optical addressability, compatibility with various quantum operations, while SiC promises higher compatibility with scalable industrial fabrication processing, and 2D materials are better suited for hybrid photonics and electronics integration. This paper provides a detailed overview of the advantages, challenges, and recent advancements in using these color centers for quantum computing. In addition, it discusses other potential color centers of interest, such as silicon (SiV) and germanium (GeV) vacancies in diamond, tin vacancies (SnV) in diamond, chromium and nickel centers in diamond, and rare‐earth ions in host materials like yttrium orthosilicate and calcium fluoride. By understanding and utilizing the properties of these diverse color centers, researchers aim to develop more efficient, scalable, and versatile quantum computers, which could lead to hybrid quantum‐classical systems that combine the strengths of different platforms and potentially transform fields like cryptography, material science, drug discovery, and complex system simulations (climate modeling, fusion energy).
Color centers associated with group-IV dopants in diamond with long-lived nuclear spins have emerged as major candidates for distributed quantum computing nodes and quantum repeaters. Several proof-of-principle experiments have already been demonstrated. A key operation for long-distance entanglement-distribution protocols are fast and robust gates between the electron spin and a nuclear spin. Here, we investigate numerically for an existing experimental platform of a Germanium-vacancy (GeV) center with a strongly-coupled 13C spin, how such gates can be implemented via quantum optimal control. In the presence of realistic noise we investigate different parameter regimes and gate operations and obtain robust two-qubit gates with fidelities exceeding 99.9%. The framework provides a scalable strategy for group-IV quantum nodes and can be adapted to related architectures.
A Quantum Repeater Platform based on Single SiV− Centers in Diamond with Cavity-Assisted, All-Optical Spin Access and Fast Coherent Driving
Quantum key distribution enables secure communication based on the principles of quantum mechanics. The distance in fiber-based quantum communication is limited to about a hundred kilometers due to signal attenuation. Thus, quantum repeaters are required to establish large-scale quantum networks. Ideal quantum repeater nodes possess a quantum memory which is efficiently connected to photons, the carrier of quantum information. Color centers in diamond and, in particular, the negatively-charged silicon-vacancy centers are promising candidates to establish such nodes. The major obstacle is an inefficient connection between the color centers spin to the Gaussian optics of fiber networks. Here, we present an efficient spin-photon interface. Individual silicon-vacancy centers coupled to the mode of a hemispherical Fabry-Pérot microcavity show Purcell-factors larger than 1 when operated in a bath of liquid Helium. We demonstrate coherent optical driving with a Rabi frequency of 290MHz and all-optical access to the electron spin in strong magnetic fields of up to 3.2T. Spin initialization within 67ns with a fidelity of 80% and a lifetime of 350ns are reached inside the cavity. The spin-photon interface is passively stable, enabled by placing a color center containing nanodiamond in the hemispherical Fabry-Pérot mirror structure and by choosing short cavity lengths. Therefore, our demonstration opens the way to realize quantum repeater applications.