Manipulating complex hybrid entanglement and testing multipartite Bell inequalities in a superconducting circuit

TL;DR

This paper demonstrates the creation and testing of a five-partite hybrid entangled state involving superconducting qubits and photonic qubits, revealing genuine multipartite quantum correlations through Bell inequality violation.

Contribution

It reports the first experimental realization of multipartite hybrid entanglement and Bell inequality violation in a superconducting circuit system.

Findings

Achieved a Bell signal of 8.381, surpassing the four-partite bound of 8.

Created a five-partite entangled state with superconducting and photonic qubits.

Confirmed genuine five-partite entanglement through Bell inequality test.

Abstract

Quantum correlations in observables of multiple systems not only are of fundamental interest, but also play a key role in quantum information processing. As a signature of these correlations, the violation of Bell inequalities has not been demonstrated with multipartite hybrid entanglement involving both continuous and discrete variables. Here we create a five-partite entangled state with three superconducting transmon qubits and two photonic qubits, each encoded in the mesoscopic field of a microwave cavity. We reveal the quantum correlations among these distinct elements by joint Wigner tomography of the two cavity fields conditional on the detection of the qubits and by test of a five-partite Bell inequality. The measured Bell signal is $8.381\pm0.038$, surpassing the bound of 8 for a four-partite entanglement imposed by quantum correlations by 10 standard deviations, demonstrating the genuine five-partite entanglement in a hybrid quantum system.