# Entanglement in a 20-Qubit Superconducting Quantum Computer

## TL;DR

This paper demonstrates the generation and detection of multi-qubit entanglement in a 20-qubit superconducting quantum computer, showcasing the system's capability for complex quantum states.

## Contribution

It reports the creation of a large-scale graph state on a 20-qubit device and the experimental verification of entanglement across various qubit groups.

## Key findings

- Connected qubits are inseparable, confirming entanglement.
- Genuine multipartite entanglement observed in chains of up to three qubits.
- Successful full state tomography on all four-qubit groups.

## Abstract

Towards realising larger scale quantum algorithms, the ability to prepare sizeable multi-qubit entangled states with full qubit control is used as a benchmark for quantum technologies. We investigate the extent to which entanglement is found within a prepared graph state on the 20-qubit superconducting quantum computer, IBM Q Poughkeepsie. We prepared a graph state along a path consisting of all twenty qubits within Poughkeepsie and performed full quantum state tomography on all groups of four connected qubits along this path. We determined that each pair of connected qubits was inseparable and hence the prepared state was entangled. Additionally, a genuine multipartite entanglement witness was measured on all qubit subpaths of the graph state and we found genuine multipartite entanglement on chains of up to three qubits.