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arXiv:2608.17470

Absorption-emission quantum repeater using diamond quantum memories

Taichi Fujiwara, Yuhei Sekiguchi, Raustin Reyes, Toshiharu Makino, Hiromitsu Kato, Hideo Kosaka

quant-phSubmitted Aug 18, 2026• Announced Aug 19, 2026• 0 citations
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Abstract

Quantum repeaters are essential for overcoming the exponential photon loss that limits entanglement generation over long distances in quantum networks. An absorption-emission-based quantum repeater exploits the fundamental light-matter interactions of a diamond nitrogen-vacancy (NV) center---photon absorption and photon emission---to transfer a quantum state from an absorbed photon to an emitted photon, offering a scalable architecture that operates without photon interference between remote nodes. Here we demonstrate an absorption-emission-based quantum repeater node using a single NV center, realizing the complete single-node operation in which heralded photon-to-memory quantum state transfer, repeat-until-success (RUS) emission of a spin-entangled photon, and quantum teleportation of the memory state onto the emitted photon constitute the essential repeater operation. By characterizing the complete repeater operation as a quantum channel from the absorbed photon to the emitted photon via quantum process tomography, we obtain a process fidelity of 78%. This demonstration establishes the absorption-emission approach as a fundamental building block for scalable quantum repeater architectures and paves the way toward practical long-distance quantum networks.

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Quantum repeaters are essential for overcoming the exponential photon loss that limits entanglement generation over long distances in quantum networks. An absorption-emission-based quantum repeater exploits the fundamental light-matter interactions of a diamond nitrogen-vacancy (NV) center---photon absorption and photon emission---to transfer a quantum state from an absorbed photon to an emitted photon, offering a scalable architecture that operates without photon interference between remote nodes. Here we demonstrate an absorption-emission-based quantum repeater node using a single NV center, realizing the complete single-node operation in which heralded photon-to-memory quantum state transfer, repeat-until-success (RUS) emission of a spin-entangled photon, and quantum teleportation of the memory state onto the emitted photon constitute the essential repeater operation. By characterizing the complete repeater operation as a quantum channel from the absorbed photon to the emitted photon via quantum process tomography, we obtain a process fidelity of 78%. This demonstration establishes the absorption-emission approach as a fundamental building block for scalable quantum repeater architectures and paves the way toward practical long-distance quantum networks.
Absorption and emission, fundamental interactions between light and matter, enable the regeneration of a quantum state of light via matter through concatenated quantum state transfer based on the principle of quantum teleportation. This transfer is enabled by electron spin-orbit entanglement and electron-nuclear spin entanglement inherent within the material. Here, we demonstrate that a photon quantum state imprinted in polarization is transferred to another photon emitted from a nitrogen vacancy (NV) center. This transfer is heralded by the result of the Bell state measurement between the electron and nitrogen nuclear spins. We show that the minimum number of incident photons needed to achieve transfer is, on average, only 0.1 photons, enabling quantum teleportation over 10 km. This demonstration paves the way for a quantum repeater that is robust against phase and intensity errors, unlike the conventional photon interference scheme, thereby facilitating practical quantum networks.
As a kind of hybrid spin system, nitrogen-vacancy (NV) centers in diamond have shown great advantages in implementing quantum registers for quantum information processing (QIP). When scaling up quantum registers to quantum networks for long-distance quantum communication and distributed quantum computation, determining how to entangle two registers in distant nodes is a basic challenge in the absence of direct interactions. In this paper, we present a scheme for entangling two distant NV centers based on the special optical absorption and emission of NV centers. In this demonstration, we transfer the entanglement information of a pair of photons to nuclear spins in NV centers and create remote NV–NV entanglement mediated by entangled photons. We then explain how to extract the entangled information from NV centers to prepare on-demand entangled photons for optical quantum information processing. The strategy of entanglement transfer between spins and photons demonstrated herein may pave the way for an NV-center-based quantum network.
We present a quantum repeater architecture using nitrogen-vacancy (NV) diamond based quantum information devices. The NV-diamond based device consists of a single negatively charged NV (NV-) center and an optical cavity. The electron of the NV center is an interface to light to be used to distribute long-distance entanglement as well as entanglement bonds for cluster state operation at each nodes. The nuclear spin-1=2 of nitrogen 15 can be used as memory. Based on this device, A scheme with as small as 10 devices to a scalable architecture is constructed, showing the necessary node technology as well as the performance such quantum communication systems.
Abstract Quantum repeaters with multiple quantum memories provide high throughput, low latency, and high fidelity quantum state (qubit) transfer over long distances. However, conventional quantum repeater protocols require full connections among the multiple quantum memories in a repeater node, which is technically challenging. Here, we propose a quantum repeater protocol based on backward propagating photon emission and absorption, where the quantum memories are multiplexed in the time-domain to speed up a single transmission channel without requiring full connectivity, thereby drastically facilitating physical implementation. Although the protocol is described with nitrogen-vacancy (NV) centers in diamond, it is applicable to various physical systems and opens up the possibility of high-speed high-fidelity quantum networks for distributed quantum computation and the quantum Internet.
We present new quantum repeater architectures based on optical modules with NV diamond centers to highlight how physical properties of these optical modules change the operations, performance and limitations of the quantum repeater systems.We focus on two different approaches to construct optical modules, and see how the properties of modules propagate to the total system. The first approach to construct the optical module is to utilize the conditional refection dependent on the electron state of the single NV center in the cavity, and the other approach is to use absorption induced teleportation from an incoming photon to the nuclear spin of the NV center. To characterize a quantum repeater system, the processes and protocols associated with photons are important.As photons are not reliable as an information carrier, i.e. quantum manipulations associated with photons are not deterministic, and the protocols and manipulations rely on post-selection to keep the fidelity of the quantum information.Post-selection is essential in quantum communications based on photons to maintain the fidelity of the communication, however it restricts the architecture of the system to be tolerant to probabilistic gates. This factor is cost intensive and is the key for the architectures to be scalable.We show that the details of how the scalability of the architectures can be affected by physical parameters of the modules.
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.