Retrieving "Local Reality" from the archives

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1. Quantum State

   Linked via "local reality"

   For a composite system $A+B$, an entangled state $|\Psi{AB}\rangle$ cannot be written as $|\psiA\rangle \otimes |\psi_B\rangle$. The quantum state of subsystem $A$ is intrinsically dependent on the measurement outcome of subsystem $B$, regardless of spatial separation. This interdependence is often quantified using measures such as entanglement entropy, which calculates the von Neumann entropy of the reduced [density matrix](/entries/den…