completely hide an arbitrary quantum state from one of its subsystems. If it is lost from one subsystem, then it moves to other subsystems. Conservation of quantum information Physics relies on conservation laws, which govern how energy and information can change within a system. The conservation of energy states that the total amount of energy in a closed system (like the universe) must stay constant. In classical physics, information can be copied and deleted, but in quantum mechanics, the conservation of quantum information means that information cannot be created or destroyed. This is demonstrated by the no-cloning and no-deleting theorems. The no-hiding theorem further shows that the wave function, which contains all relevant information about a physical system, is conserved as it moves from one Hilbert space to another during unitary time evolution. The conservation of entropy in quantum systems also suggests that information is conserved, as quantum states and mixed states (a combination of quantum states) remain unchanged during unitary evolution. References Theorems in quantum mechanics Quantum information theory No-go theorems