🚀 go-pugleaf

Drexler's proposed rod logic dissipates about 10**-21 joules per "lock"
operation (roughly equivalent to a gate operation).  This is very small by
present day standards.  Interestingly, K. K. Likharev proposed a fully
reversible device, the PQ (Parametric Quantron), based on Josephson
Junction device technology, which dissipates 10**-24 joules per operation
when operated at 4 degrees Kelvin at a speed of 10**-9 seconds (1
nanosecond) per operation.  This compares with rod-logic dissipating about
10**-21 joules at 300 degrees Kelvin at a speed of 50 x 10**-12 seconds (50
picoseconds) per operation.

This comparison is not, strictly speaking, apples and apples.  By lowering
the speed of Drexler's rod-logic (or raising the speed of Likharev's PQ)
and by lowering the temperature around the rods, the difference in energy
dissipation largely disappears.  Still, I do not believe Likharev's
proposal is widely known in the nanotechnology community, nor is there any
particular reason to believe either proposal is "optimal," in the sense of
dissipating minimal energy per logic operation at a given speed and
temperature of operation.

Can anyone propose (or has anyone heard of) a device that can be built from
atoms which has lower energy dissipation per logic operation?  Note that
all such devices will have to be fully reversible (see:  The Fundamental
Physical Limits of Computation, by Charles H. Bennett and Rolf Landauer,
Scientific American, Vol. 253, July 1985, pages 48-56).

Reference:  "Classical and Quantum Limitations on Energy Consumption in
Computation" by K. K. Likharev, International Journal of Theoretical
Physics, Vol. 21, Nos. 3/4, 1982, pages 311-326.