Oxford trapped-ion distributed-compute demonstration

What it is

Each module is an ion trap holding two species of ion. A ⁸⁸Sr⁺ ion acts as the network qubit: its optical transition is matched to the photonic interface, so it can emit a photon entangled with its internal state. A ⁴³Ca⁺ ion in the same trap acts as the circuit qubit: it carries the computational state, supports long-lived coherence, and is coupled to the ⁸⁸Sr⁺ network qubit via a local two-qubit gate inside the module. ^{Main et al. 2025}

To produce a Bell pair between the two modules, each ⁸⁸Sr⁺ ion emits a photon entangled with its spin state; the two photons interfere on a beam splitter midway between the modules, and a coincident detection projects the two ⁸⁸Sr⁺ ions into a Bell pair (the Barrett-Kok-style heralding protocol). Each module then swaps that entanglement onto its ⁴³Ca⁺ circuit qubit through the local inter-species gate, leaving a Bell pair between the two computational qubits. Consuming that Bell pair together with two bits of classical communication implements a deterministic CNOT between the two circuit qubits — gate teleportation in the sense of Gottesman and Chuang. ^{Main et al. 2025}

With the inter-module CNOT in hand, the team ran a two-qubit instance of Grover's search distributed across the two modules. The oracle and the diffusion step both require entangling operations between the two circuit qubits, and those are supplied by the teleported CNOT rather than by a single shared trap. The end-to-end algorithm succeeds with the success probability expected from the constituent gate fidelities, demonstrating that the network link can carry a full algorithmic workload, not just one isolated entangling operation.

Verified claims

• Two trapped-ion modules connected by a ~2 m optical link, with heralded photonic entanglement between the two modules' ⁸⁸Sr⁺ network qubits. ^{Main et al. 2025}
• Mixed-species architecture per module — ⁸⁸Sr⁺ as the photonic-interface (network) qubit, ⁴³Ca⁺ as the long-coherence circuit qubit, with a local inter-species gate connecting them. ^{Main et al. 2025}
• Deterministic teleported CNOT between the two ⁴³Ca⁺ circuit qubits, with reported gate fidelity ~86 %. ^{Main et al. 2025}
• Two-qubit Grover's search executed across the two modules, with the inter-module entangling step supplied by the teleported CNOT. ^{Main et al. 2025}
• First distributed quantum algorithm executed across two physically separate quantum-computing modules — the entanglement link is consumed to perform algorithmic gates, not just to certify a Bell pair. ^{Main et al. 2025}

Things to note

• ~2 m link inside a single laboratory. The two modules sit in the same room, connected by a short free-space / fibre optical path. Loss, dispersion, and phase drift over a deployed metro fibre are outside the scope of this demonstration.
• ~86 % teleported-CNOT fidelity. Fault-tolerant distributed computation will need this gate well above an error-correction threshold; the present fidelity establishes the primitive rather than a production-level operation.
• Each module is a full ion-trap apparatus. Vacuum chambers, laser racks, control electronics, and imaging optics occupy room-scale benches. Packaging the modules into rack-scale network nodes is separate engineering work.
• Distinct from Knaut and Pompili. The Boston SiV loop (Knaut et al., 2024) and the Delft three-node NV network (Pompili et al., 2021) entangle matter qubits across a link but do not consume that entanglement to teleport a gate between two computational processors. The Oxford demonstration closes that loop end-to-end.
• Scope of the demonstration. One link, two modules, one laboratory. The work shows the gate-teleportation primitive that a future distributed quantum computer would rely on, rather than a multi-user network.

Related entries

• Teleportation — the gate-teleportation primitive that turns a shared Bell pair plus classical communication into a remote CNOT.
• Entanglement distribution — MeetInTheMiddle architecture with a midpoint beam-splitter Bell-state measurement; the protocol used here to entangle the two ⁸⁸Sr⁺ network qubits.
• Quantum repeaters — the mixed-species "network qubit + circuit qubit" pattern is the same architecture future 1G / 2G repeater nodes will use.
• Harvard SiV Boston-metro loop — matter-qubit entanglement over deployed fibre, without the teleported-gate step.
• Delft NV three-node network — academic three-node entanglement + swapping reference; sibling matter-qubit demonstration.
• Cisco × Qunnect Brooklyn–Manhattan — entanglement distribution over deployed metro fibre, without quantum memory or teleported gates.
• Companies — Oxford Ionics and Universal Quantum sit nearby in the trapped-ion vendor landscape.