Large-scale entanglement in superconducting quantum devices

The ability to prepare sizeable multi-qubit entangled states with full qubit control is a benchmark for the development of near-term quantum computers. We demonstrate two forms of entanglement within IBM Quantum devices: entanglement in the sense of inseparability with fixed qubit bipartitions, and the stricter genuine multipartite entanglement (GME) which is the inability to express the state as a mixture of only product pure states. A graph state was prepared along a line on all 20 qubits of the ibmq_poughkeepsie device. Each neighbouring pair of qubits was found to be inseparable, indicating entanglement across the device. On the 65-qubit ibmq_manhattan device, a native graph state was prepared and entanglement was detected for all neighbouring pairs of qubits. A parity verification method was implemented for Greenberger-Horne-Zeilinger states on the 27-qubit ibmq_montreal device and an average fidelity increase of up to 0.056+-0.023 was observed. Additionally, a fidelity of 0.61+-0.05 was measured on a 27-qubit state demonstrating GME across the entire device.