Quantum entanglement: Violation of Bell's inequality on frequency-bin entangled photon pairs

Making use of a specifically-developed slow light technique to reduce the velocity of light dramatically, researchers implemented a Bell Test and were able to generate frequency-bin entangled narrowband biphotons from spontaneous four-wave mixing (SFWM) in cold atoms with a double-path configuration, where the phase difference between the two spatial paths can be controlled independently and nonlocally.