action of opening the box and checking the physical position of the coin yields the qubit projection |H> or |T), which corresponds to either of the classical bits 0 = heads or 1 = tails, respectively, with equal probabilities. This measurement is seen to collapse the coin state 1q) into one of its elementary states |HY or |T), which yields the observable value referred to as heads or tails. The counterintuitive, or nonclassical, conclusion is that as long as no measurement (or state collapse) is effected, the coin dwells in the superposition of states defined by Eq. (16.6). Note that this superposition is often referred to as 1+), or "cat state," as I shall explain. It is possible to think of many other examples of superpositions of states. For instance, consider a toddler in her room on an early Sunday morning. Is she still sleeping (state |S>) or is she awake and playing (state |A))? By 8 a.m. the parents know that there is a fair chance that she must be asleep, say 90%. By 9 a.m., they know that the odds are 50%. But if the parents don't get up and check, the quantum view is that by 8 a.m., the child must be in the state S)/V0.9 + |A>/0.1 and by 9 a.m. in the state (S. + |A))/2, which we have called the state |+). Only by opening the child's bedroom door can the actual measurement be made, which results in the state collapse into |S) or |A), giving the classical information 0 = sleeping or 1 = awake. As uncanny as this example may sound, it illustrates the quantum concept of "superposition of states," now with the notion of a time evolution from the initial pure state |S) to the final pure state |A). One may view our example as a gentler, yet conceptually equivalent, version of the Schrödinger's cat thought experiment. The stories of the tossed coin, In a thought experiment, Schrödinger imagines a cat that is placed inside a sealed box. The box contains a can of poison gas, a radioactive substance, and a Geiger counter. The decay rate of the radioactive substance is such that after one hour, there is a 50% cha