Generating and detecting Genuine Multipartite Entanglement (GME) of sizeable quantum states prepared on physical devices is an important benchmark for highlighting the progress of near-term quantum computers.
A common approach to certify GME is to prepare a Greenberger-Horne-Zeilinger (GHZ) state and measure a GHZ fidelity of at least 0.5.
A team at University of Melbourne has measured the fidelities using multiple quantum coherences of GHZ states on 11 to 27 qubits prepared on the IBM Quantum ibmq_montreal device.
Combinations of Quantum Readout Error Mitigation (QREM) and parity verification error detection are applied to the states. A fidelity of 0.61±0.05 with 95% confidence was recorded for a 27-qubit GHZ state when QREM was used, demonstrating GME across the full device.
They benchmarked the effect of parity verification on GHZ fidelity for two GHZ state preparation embeddings on the heavy-hexagon architecture.
The results showed that the effect of parity verification, while relatively modest, led to a detectable improvement of GHZ fidelity.