# Verifying Multipartite Entangled GHZ States via Multiple Quantum Coherences

## TL;DR

This paper introduces a scalable, noise-robust method for verifying multipartite entanglement in quantum systems, demonstrated on a 20-qubit superconducting device with high fidelity for an 18-qubit GHZ state.

## Contribution

The paper develops a new entanglement metric based on multiple quantum coherences and demonstrates its effectiveness on a large superconducting quantum device.

## Key findings

- Achieved 0.5165 fidelity for an 18-qubit GHZ state
- The metric is robust to noise and easy to implement
- Verified multipartite entanglement across 18 qubits

## Abstract

The ability to generate and verify multipartite entanglement is an important benchmark for near-term quantum devices devices. We develop a scalable entanglement metric based on multiple quantum coherences, and demonstrate experimentally on a 20-qubit superconducting device - the IBM Q System One. We report a state fidelity of 0.5165$\pm$0.0036 for an 18-qubit GHZ state, indicating multipartite entanglement across all 18 qubits. Our entanglement metric is robust to noise and only requires measuring the population in the ground state; it can be readily applied to other quantum devices to verify multipartite entanglement.