Читать книгу Principles of Superconducting Quantum Computers - Daniel D. Stancil - Страница 17

Classical NOT gates are reversible; i.e., two NOT gates in series returns the bit to its original state. However, the situation is different for classical logic gates with multiple inputs. As an example, consider the NAND Gate shown in Figure 1.2. It is not possible to uniquely determine the input bits from the output bit. Because of this, conventional multi-input logic is irreversible.²

Figure 1.2 NAND circuit diagram.

In contrast, quantum gates are reversible. As a result, even though the output overwrites the input, the input is not lost since the effect of a series of gate operations can be reversed by applying the appropriate inverse operations.