Quantum computers will perform computations at the atomic scale [5,6]. Fig. 1 shows a survey made by Keyes in 1988 : The number of dopant impurities required for logic in the bases of bipolar transistors is plotted against the year. This plot may be thought of as showing the number of electrons required to store a single bit of information. An extrapolation of the plot suggests that we might be within the reach of atomic-scale computations within the next two decades.
Fig. 1 Plot from Ref.  showing the number of dopant impurities involved in logic in bipolar transistors with year. (Copyright 1988 by International Business Machines Corporation, reprinted with permission.)