Deterministic multi-qubit entanglement in a quantum network

High-fidelity deterministic quantum state transfer and multi-qubit entanglement are demonstrated in a quantum network comprising two superconducting quantum nodes one metre apart, with each node including three interconnected qubits. The generation of high-fidelity distributed multi-qubit entanglement is a challenging task for large-scale quantum communication and computational networks(1-4). The deterministic entanglement of two remote qubits has recently been demonstrated with both photons(5-10) and phonons(11). However, the deterministic generation and transmission of multi-qubit entanglement has not been demonstrated, primarily owing to limited state-transfer fidelities. Here we report a quantum network comprising two superconducting quantum nodes connected by a one-metre-long superconducting coaxial cable, where each node includes three interconnected qubits. By directly connecting the cable to one qubit in each node, we transfer quantum states between the nodes with a process fidelity of 0.911 +/- 0.008. We also prepare a three-qubit Greenberger-Horne-Zeilinger (GHZ) state(12-14) in one node and deterministically transfer this state to the other node, with a transferred-state fidelity of 0.656 +/- 0.014. We further use this system to deterministically generate a globally distributed two-node, six-qubit GHZ state with a state fidelity of 0.722 +/- 0.021. The GHZ state fidelities are clearly above the threshold of 1/2 for genuine multipartite entanglement(15), showing that this architecture can be used to coherently link together multiple superconducting quantum processors, providing a modular approach for building large-scale quantum computers(16,17).

Automated summary

High-fidelity deterministic quantum state transfer and multi-qubit entanglement were demonstrated in a quantum network consisting of two superconducting quantum nodes connected by a one-meter-long superconducting coaxial cable. This work successfully achieved the deterministic generation and transmission of multi-qubit entanglement with high state fidelities, showing the potential for building large-scale quantum computers through modular linking of superconducting quantum processors.