Achieving the entanglement measurement of the W state. Credit: KyotoU / Takeuchi lab Quantum entanglement is one of the strangest features of the quantum world. It describes a situation in which particles such as photons are so deeply linked that their properties cannot be fully understood one by one. Instead, the system has to be treated as a whole. That idea sharply conflicts with the classical view that every particle should carry its own independent reality, a conflict that famously