Unrealistic later we will look at it briey 11 they

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Unformatted text preview: T described computation with idealized, perfectly elastic balls reflecting o↵ barriers. Minimum dissipation, propelled by (conserved) momentum. Unrealistic. Later we will look at it briefly. ¶11. They suggested a more realistic implementation involving “charge packets bouncing around along inductive paths between capacitors.” ¶12. Richard Feynman (CalTech) had been interacting with IM group, and developed “a full quantum model of a serial reversible computer” (Feynman, 1986). ¶13. Adiabatic circuit: Since 1980s there has been work in adiabatic circuits, esp. in 1990s. An adiabatic process takes place without input or dissipation of energy. Adiabatic circuits minimize energy use by obeying certain circuit design rules. “[A]rbitrary, pipelined, sequential logic could be implemented in a fully-reversible fashion, limited only by the energy coe cients and leakage currents of the underlying transistors.” 52 CHAPTER II. PHYSICS OF COMPUTATION ¶14. As of 2004, est. cE = 3 meV/kHz, about 250⇥ less than DNA. ¶15. “It is di cult to tell for certain, but a wide variety of post-transistor device technologies have been proposed . . . that have energy coe cients ranging from 105 to 1012 times lower than present-day CMOS! This translates to logic circuits that could run at GHz to THz frequencies, with dissipation per op that is still less (in some cases orders of magnitude less) than the VNL bound of kB T ln 2 . . . that applies to all irreversible logic technologies. Some of these new device ideas have even been prototyped in laboratory experiments [2001].” ¶16. “Fully-reversible processor architectures [1998] and instruction sets [1999] have been designed and implemented in silicon.” ¶17. But this is more the topic of a CpE course. . . C.2 Physical assumptions of computing These lectures are based primarily on Edward Fredkin and Tommaso To↵oli’s “Conservative logic” (Fredkin & To↵oli, 1982). C.2.a Dissipative logic ¶1. The following physical principles are implicit in the existing theory of computation. ¶2. P1. The speed of propaga...
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