Delft three-node NV-centre network
The first multi-node entanglement-based quantum network: three nitrogen-vacancy (NV) memory nodes — Alice, Bob, and Charlie — linked by photons, with the middle node Bob acting as a swap relay so that Alice and Charlie can share entanglement without ever exchanging a photon directly. Demonstrated entanglement distribution and entanglement swapping in 2021; qubit teleportation between non-neighbouring nodes in 2022.
What it is
Each of the three nodes is an NV centre in diamond — a nitrogen atom adjacent to a lattice vacancy — used as the communication qubit, with a nearby nuclear spin as a robust memory qubit and local quantum-gate primitive. Alice ↔ Bob and Bob ↔ Charlie share phase-stabilised optical links; entanglement is heralded between neighbour pairs, then Bob performs a Bell-state measurement on his two communication qubits to swap the entanglement so Alice and Charlie end up sharing a Bell pair. Pompili et al. 2021
The 2022 follow-up upgraded the protocol to deterministic qubit teleportation between non-neighbours: Alice teleports an arbitrary unknown qubit state to Charlie using only locally-shared Bell pairs and classical communication through Bob, with no direct optical link between Alice and Charlie. Hermans et al. 2022 That is the elementary quantum-internet primitive — sending an unknown qubit through a Bell pair plus two classical bits — running end-to-end on a real three-node fabric.
Published papers
The Delft network is one platform reported across a sequence of papers, each removing a barrier the next result depends on.
| Year | Paper | Result | What it implies |
|---|---|---|---|
| 2015 | Hensen et al., Nature 526.682 Hensen et al. 2015 | Loophole-free Bell-inequality violation between two NV electron spins 1.3 km apart. | The nodes can be remotely entangled at all, with heralded success — the precondition for everything that follows. |
| 2018 | Humphreys et al., Nature 558.268 Humphreys et al. 2018 | Deterministic, on-demand delivery of remote entanglement between two nodes. | Entanglement arrives when the protocol asks for it, not only when a heralding click happens to land — fast enough to chain into a multi-node sequence. |
| 2021 | Pompili et al., Science 372.259 Pompili et al. 2021 | Three-node network (Alice–Bob–Charlie); entanglement distribution plus a Bell-state measurement at Bob to swap. | The building blocks compose — a middle node links two others that never exchange a photon. First multinode entanglement-based network. |
| 2022 | Pompili et al., npj QI 8.121 Pompili et al. 2022 | Entanglement delivered through an explicit physical- and link-layer network stack. | The network runs on a layered protocol stack rather than bespoke lab control — the experimental counterpart to RFC 9340's link-layer service. |
| 2022 | Hermans et al., Nature 605.663 Hermans et al. 2022 | Deterministic qubit teleportation between the non-neighbouring nodes Alice and Charlie, via Bob. | The elementary quantum-internet primitive — moving an unknown qubit with a Bell pair and two classical bits — runs end-to-end on a real multi-node fabric. |
Verified claims
- First entanglement-based network with three nodes. Published in Science 372.259 (2021). The "first multinode quantum network of remote solid-state qubits" framing is the authors' own. Pompili et al. 2021
- Entanglement distribution + entanglement swapping at Bob. Both protocols ran on the platform in the 2021 paper. Pompili et al. 2021
- 2022 follow-up: qubit teleportation between Alice and Charlie. Reported by Hermans et al., Nature 605.663 (2022). First end-to-end teleportation between non-neighbouring nodes. Hermans et al. 2022
- NV-centre platform with auxiliary nuclear-spin memory qubits. The robust memory was essential for the swap protocol to succeed against the heralding-rate / memory-decoherence trade-off. Pompili et al. 2021
Things to note
- Setting. The three nodes sit in the same building, with the optical links running on a lab bench. The contribution is architectural rather than geographic.
- Rates. Heralded entanglement between two NV centres runs at the 1–10 Hz scale; end-to-end teleportation rates in 2022 are lower still. The platform demonstrates the protocols rather than throughput.
- Scope. The Delft fabric is a kernel demonstration that the building blocks compose; it is not yet offered as a service to other QuTech labs or outside users.
- Relation between the two papers. The 2022 teleportation result uses the 2021 swap as a subroutine. Both papers describe the same physical platform as sequential milestones on the same setup.