# Observation of multi-component atomic Schr\"odinger cat states of up to 20 qubits

## TL;DR

This paper reports the deterministic creation of large-scale multi-component atomic Schr"odinger cat states and GHZ states with up to 20 qubits on a superconducting quantum processor, demonstrating advanced control over multipartite entanglement.

## Contribution

The work introduces a method to generate and observe multi-component atomic Schr"odinger cat states of up to 20 qubits, the largest entanglement created in solid-state systems to date.

## Key findings

- Successfully generated 18-qubit GHZ state with high fidelity
- Created atomic Schr"odinger cat states of up to 20 qubits
- Demonstrated controllable multipartite entanglement in a superconducting processor

## Abstract

We report on deterministic generation of 18-qubit genuinely entangled Greenberger-Horne-Zeilinger (GHZ) state and multi-component atomic Schr\"{o}dinger cat states of up to 20 qubits on a quantum processor, which features 20 superconducting qubits interconnected by a bus resonator. By engineering a one-axis twisting Hamiltonian enabled by the resonator-mediated interactions, the system of qubits initialized coherently evolves to an over-squeezed, non-Gaussian regime, where atomic Schr\"{o}dinger cat states, i.e., superpositions of atomic coherent states including GHZ state, appear at specific time intervals in excellent agreement with theory. With high controllability, we are able to take snapshots of the dynamics by plotting quasidistribution $Q$-functions of the 20-qubit atomic cat states, and globally characterize the 18-qubit GHZ state which yields a fidelity of $0.525\pm0.005$ confirming genuine eighteen-partite entanglement. Our results demonstrate the largest entanglement controllably created so far in solid state architectures, and the process of generating and detecting multipartite entanglement may promise applications in practical quantum metrology, quantum information processing and quantum computation.