Violating Bell’s inequality with remotely connected superconducting qubits

Quantum communication relies on the efficient generation of entanglement between remote quantum nodes, as entanglement is required to achieve and verify secure communications 1 . Remote entanglement has been realized using a number of different probabilistic schemes 2 , 3 , but deterministic remote entanglement has only been demonstrated recently, using a variety of superconducting circuit approaches 4 – 6 . However, the deterministic violation of a Bell inequality 7 , a strong measure of quantum correlation, has not been demonstrated so far in a superconducting quantum communication architecture, in part because achieving sufficiently strong correlation requires fast and accurate control of the emission and capture of the entangling photons. Here, we present a simple and robust architecture for achieving this benchmark result in a superconducting system. A deterministic violation of the Bell inequality is reported between two superconducting circuits, providing a necessary test for establishing strong enough quantum entanglement to achieve secure quantum communications.