Yes indeed this sentence seems very wrong to me as well: The author seems to mistake entanglement for superposition. The former describes a quantum state that i

Yes indeed this sentence seems very wrong to me as well: The author seems to mistake entanglement for superposition. The former describes a quantum state that involves TWO quantum systems whose wave functions are "intertwined" such that you cannot write it as a simple product of the wavefunction of either system (a so-called "product state"), and which thus produces some seemingly paradoxical effects (e.g. the famous Einstein-Podolsky-Rosen paradox). Superposition, on the other hand, means that a SINGLE quantum system can have a wave function in which the system is in more than one possible state at once. Or, in mathematical terms, here's an entangled state |\psi> = 0.5^(1/2)(|0>|1> + |1>|0>) If we would make a measurement of the first quantum state, we would project it to either the |0> or the |1> state. This would result in the state of the other system to be projected into either the |1> or the |0> state, respectively. So there is some strange, "spooky" action between the two seemingly independent states. Here is a superposition state for comparison: |\psi> = 0.5^(1/2)(|0>+|1>) Note that it involves only a single quantum system, which has a 50 % amplitude in either of the states 0 or 1. Wikipedia has some good definitions of entanglement and superposition: https://en.wikipedia.org/wiki/Quantum_entanglement https://en.wikipedia.org/wiki/Quantum_entanglement https://en.wikipedia.org/wiki/Quantum_superposition https://en.wikipedia.org/wiki/Quantum_superposition