Neutrinos are the true ghosts of the microcosm. Nearly massless and chargeless, they pass through planets as if through empty space. But inside each neutrino hides not one particle but three — three 'flavors' (electron, muon, and tau) that constantly morph into one another. This dance is called oscillation.

The authors of the study viewed this dance as quantum entanglement among the three flavors. It turns out that an oscillating neutrino is not just a mixture but a full-fledged tripartite entangled state from the W class. Such states are robust: even if one part disappears, the remaining parts retain their connection. Most striking, this entanglement does not vanish when the neutrino loses coherence (the sharpness of its wave properties) due to interactions with the environment.

The scientists also found that CP phases, special parameters that distinguish matter from antimatter, affect the degree of entanglement. This means that neutrino entanglement could reveal fundamental symmetries of the Universe. For astrophysical neutrinos, which travel for billions of years from distant galaxies, such robust entanglement could become a tool for quantum communication over cosmic distances.