Taichi Fujiwara and colleagues have achieved complete operation of an absorption-emission quantum repeater node utilising a single diamond nitrogen-vacancy (NV) centre, extending previous work lacking a repeat-until-success emission protocol. Integrating heralded photon absorption with this protocol, repeating the process until success, increases photon collection efficiency approximately tenfold compared to earlier attempts. The team attained a process fidelity of seventy-eight per cent, validating this approach as viable for constructing scalable long-distance quantum networks.

Taichi Fujiwara and colleagues created a functional component for quantum technology that enables secure long-distance communication by overcoming signal loss. This device transfers information carried by individual photons into a diamond crystal, then retrieves and re-emits it as new photons without errors occurring approximately twenty-two per cent of the time. Employing a ‘repeat-until-success’ method, repeatedly attempting data transfer until accurate transmission is achieved, increases efficiency relative to previous designs.

Taichi Fujiwara and colleagues unveiled a key component for future quantum networks; functioning similarly to a traditional telephone repeater but boosting fragile quantum signals instead of conventional ones, this allows them to travel further without degradation or information loss. The team successfully demonstrated complete operation of a ‘quantum repeater node’ utilising a single diamond containing a nitrogen-vacancy (NV) centre, a tiny defect within the diamond acting as an artificial atom capable of storing and manipulating quantum data.

This advancement overcomes limitations imposed by signal loss over long distances, enabling secure communication through entanglement transfer via photons. Achieving seventy-eight per cent process fidelity, determined using techniques akin to thorough diagnostic tests on the system, validates its potential for building scalable networks, though optimisation and integration with existing infrastructure remain considerations before widespread deployment is feasible.

High-fidelity entanglement via repeat-until-success protocol using a diamond nitrogen-vacancy centre

Process fidelities reached seventy-eight per cent, representing a substantial improvement over previous quantum repeater nodes lacking a repeat-until-success emission protocol; this threshold validates practical long-distance entanglement generation previously hampered by signal loss. Increasing photon collection efficiency approximately tenfold allows reliable data transmission where it was once improbable due to inherent inefficiencies in light-matter interactions, surpassing single excitation attempts.

The team at Advanced Power Electronics Research Centre and collaborating institutions completed operation of an ‘absorption-emission’ based node utilising a diamond nitrogen-vacancy (NV) centre, a tiny defect within the crystal acting as an artificial atom for storing quantum information.

A process fidelity averaging seventy-eight per cent was achieved when transferring quantum information from absorbed photons to emitted ones via a diamond’s nitrogen-vacancy (NV) centre; this indicates precise control over atomic properties within the crystal lattice. Maintaining coherence during repeated excitation cycles necessitated careful synchronisation with the hyperfine period of the NV centre, optimising repetition periods for maximum preservation of the stored quantum state.

Seventy-eight per cent accuracy in preserving arbitrary nuclear-spin states was demonstrated by limiting excitation attempts while balancing fidelity against photon collection efficiency. These results currently depend on carefully calibrated laboratory conditions and do not yet account for signal degradation or decoherence effects anticipated in real-world network environments.

High fidelity nitrogen-vacancy centre operation validates repeater node functionality

A single absorption-emission based quantum repeater node utilising a diamond nitrogen-vacancy (NV) centre has been fully operated, achieving 78 percent process fidelity through quantum process tomography which fully characterizes the quantum channel from absorbed to emitted photons. This measurement confirms successful data transmission within that isolated component and establishes this approach as viable for building scalable long-distance networks; however it does not demonstrate entanglement distribution between multiple nodes nor over any significant distance.

The team highlights their method relaxes stringent requirements around optical synchronisation needed by other approaches such as interference or scattering based schemes. Integrating heralded photon absorption, detecting an incoming photon and confirming its reception, with memory preservation throughout the repeat emission cycle defines the demonstrated repeater node.

Diamond nitrogen-vacancy centres enable high-fidelity quantum repeater functionality

Scientists completed operation of a quantum repeater node using a single diamond nitrogen-vacancy (NV) centre, achieving 78% process fidelity through quantum process tomography; this NV centre is a defect within the diamond’s crystal structure exhibiting unique light-sensitive properties. Successfully integrating heralded photon transfer and teleportation of memory states onto emitted photons represents an advance in building scalable long-distance quantum networks, addressing exponential photon loss which severely limits entanglement generation over distance, a fundamental challenge for practical quantum communication.

The authors acknowledge previous work utilising single atoms trapped in optical cavities to achieve reversible mapping of photonic qubits into atomic memories, alongside heralded storage and state transfer between remote atoms via single photon exchange.

Heralded absorption of photonic qubits has also been previously demonstrated using charged quantum dots, semiconductor nanocrystals exhibiting unique electrical properties; these earlier approaches provided foundations upon which the current method builds its repeater node functionality but lacked efficiency gains offered by this new approach. The RUS approach enhances entanglement generation rates, a key metric for practical applications, by repeatedly attempting emission until success is achieved and addresses a major bottleneck in scaling these systems.

Currently, the team’s work demonstrates operation within one individual node and does not yet show distribution of entanglement between multiple nodes or over any significant distance. Achieving seventy eight per cent process fidelity validates the architecture’s potential within scalable long-distance networks by overcoming signal degradation inherent in optical fibres; this represents a critical step towards practical implementation. While current research focuses on single node operation, establishing these principles opens questions regarding multi-node entanglement distribution and mitigating decoherence effects essential for building truly global quantum communication systems.

The researchers successfully demonstrated complete quantum repeater operation using a single diamond nitrogen-vacancy (NV) center, achieving 78% process fidelity during state transfer from an absorbed photon to an emitted one. This result confirms that utilising light-matter interactions with NV centers offers a viable method for extending the range of quantum networks by addressing exponential photon loss. The demonstration incorporates a repeat-until-success emission protocol which improves efficiency compared to previous attempts at single excitation. Authors suggest future work will focus on distributing entanglement between multiple nodes and tackling challenges related to signal degradation over distance.

👉 More information
🗞 Absorption-emission quantum repeater using diamond quantum memories
✍️ Taichi Fujiwara, Yuhei Sekiguchi, Raustin Reyes, Toshiharu Makino, Hiromitsu Kato and Hideo Kosaka
🧠 ArXiv: https://arxiv.org/abs/2608.17470

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