The distribution of entangled states across the nodes of a future quantum internet will unlock fundamentally new technologies. Here, we report on the realization of a three-node entanglement-based quantum network. We combine remote quantum nodes based on diamond communication qubits into a scalable phase-stabilized architecture, supplemented with a robust memory qubit and local quantum logic. In addition, we achieve real-time communication and feed-forward gate operations across the network. We demonstrate two quantum network protocols without postselection: the distribution of genuine multipartite entangled states across the three nodes and entanglement swapping through an intermediary node. Our work establishes a key platform for exploring, testing, and developing multinode quantum network protocols and a quantum network control stack.

Future quantum internet applications will derive their power from the ability to share quantum information across the network1,2. Quantum teleportation allows for the reliable transfer of quantum information between distant nodes, even in the presence of highly lossy network connections3. Although many experimental demonstrations have been performed on different quantum network platforms4–10, moving beyond directly connected nodes has, so far, been hindered by the demanding requirements on the pre-shared remote entanglement, joint qubit readout and coherence times. Here we realize quantum teleportation between remote, non-neighbouring nodes in a quantum network. The network uses three optically connected nodes based on solid-state spin qubits. The teleporter is prepared by establishing remote entanglement on the two links, followed by entanglement swapping on the middle node and storage in a memory qubit. We demonstrate that, once successful preparation of the teleporter is heralded, arbitrary qubit states can be teleported with fidelity above the classical bound, even with unit efficiency. These results are enabled by key innovations in the qubit readout procedure, active memory qubit protection during entanglement generation and tailored heralding that reduces remote entanglement infidelities. Our work demonstrates a prime building block for future quantum networks and opens the door to exploring teleportation-based multi-node protocols and applications2,11–13.

We report on the realization and verification of quantum entanglement between an NV electron spin qubit and a telecom-band photonic qubit. First we generate entanglement between the spin qubit and a 637 nm photonic time-bin qubit, followed by photonic quantum frequency conversion that transfers the entanglement to a 1588 nm photon. We characterize the resulting state by correlation measurements in different bases and find a lower bound to the Bell state fidelity of ≥ 0.77 ± 0.03. This result presents an important step towards extending quantum networks via optical fiber infrastructure.Quantum networks connecting and entangling longlived qubits via photonic channels [1] may enable new experiments in quantum science as well as a range of applications such as secure information exchange between multiple nodes, distributed quantum computing, clock synchronization, and quantum sensor networks [2][3][4][5][6][7][8][9][10]. A key building block for long-distance entanglement distribution via optical fibers is the generation of entanglement between a long-lived qubit and a photonic telecomwavelength qubit (see Fig. 1a). Such building blocks are now actively explored for various qubit platforms [11][12][13][14][15][16].The NV center in diamond is a promising candidate to act as a node in such quantum networks thanks to a combination of long spin coherence and spin-selective optical transitions that allow for high fidelity initialization and single-shot read out [17]. Moreover, memory qubits are provided in the form of surrounding carbon-13 nuclear spins. These have been employed for demonstrations of quantum error correction [18][19][20] and entanglement distillation [21]. Heralded entanglement between separate NV center spin qubits has been achieved by generating spin-photon entangled states followed by a joint measurement on the photons [22].Extending such entanglement distribution over long distances is severely hindered by photon loss in the fibers. The wavelength at which the NV center emits resonant photons, the so-called zero-phonon-line (ZPL) at 637 nm, exhibits high attenuation in optical glass fibers. Quantum-coherent frequency conversion to the telecom band can mitigate these losses by roughly 7 orders of magnitude for a distance of 10 km [23,24] and would enable the quantum network to optimally benefit from the existing telecom fiber infrastructure. Recently, we have realized the conversion of 637 nm NV photons to * These two authors contributed equally to this work. † R.Hanson@tudelft.nl 1588 nm (in the telecom L-band) using a difference frequency generation (DFG) process and shown that the intrinsic single-photon character is maintained during this process [25]. However, for entanglement distribution an additional critical requirement is that the quantum information encoded by the photon is preserved during the frequency conversion.Here we demonstrate entanglement between an NV center spin qubit and a time-bin encoded frequencyconverted photonic qubit at telecom wavelength. The concept of our experiment is d...