The Relationship Between Classical and Quantum Computing

The discussion in the previous sections leads to the interesting question about the relationship between classical computing and quantum computing. The indistinct boundary between quantum states and quantum measurements carries over to that relationship. In one of the previous chapters, we said that classical computing states—the high voltages and low voltages in the typical modern computer—are persistent states: We can look at them to determine what gates should be doing, and we can connect them with wires to many gates at the same time without disturbing the state. In fact, with most computers today, you can turn off the computer and when you turn it back on, it remembers what you had been doing just before you turned it off. The classical computing states are nothing if not persistent.