Abstract: Until recently, the paradigm of computing was the Turing machine and its numerous equivalents. All operations are made with state machines. Each operation is irreversible and brings about an increase of entropy and, therefore, an expenditure of energy of at least kTln2 per bit. We show that optics allows the first practical quantum mechanical digital processors. These processors require digital input and produce digital output but need no intermediate state machines. We show that, in the sense of not requiring material devices which would otherwise be required, nothing is superior to something for computing. !4
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