Editing Reversible computing (section)

==Physical reversibility==
Landauer's principle (and indeed, the [[second law of thermodynamics]]) can also be understood to be a direct [[logical consequence]] of the underlying [[CPT symmetry|reversibility of physics]], as is reflected in the [[Hamiltonian mechanics|general Hamiltonian formulation of mechanics]], and in the [[time evolution|unitary time-evolution operator]] of [[quantum mechanics]] more specifically.<ref>{{Cite journal |last1=Frank |first1=Michael P. |last2=Shukla |first2=Karpur |date=June 1, 2021 |title=Quantum Foundations of Classical Reversible Computing |journal=Entropy |language=en |volume=23 |issue=6 |pages=701 |doi=10.3390/e23060701 |issn=1099-4300 |pmc=8228632 |pmid=34206044 |arxiv=2105.00065 |bibcode=2021Entrp..23..701F |doi-access=free }}</ref>

The implementation of reversible computing thus amounts to learning how to characterize and control the physical dynamics of mechanisms to carry out desired computational operations so precisely that the experiment accumulates a negligible total amount of uncertainty regarding the complete physical state of the mechanism, per each logic operation that is performed. In other words, precisely track the state of the active energy that is involved in carrying out computational operations within the machine, and design the machine so that the majority of this energy is recovered in an organized form that can be reused for subsequent operations, rather than being permitted to dissipate into the form of heat.

Although achieving this goal presents a significant challenge for the design, manufacturing, and characterization of ultra-precise new physical mechanisms for [[computing]], there is at present no fundamental reason to think that this goal cannot eventually be accomplished, allowing someday to build computers that generate much less than 1 bit's worth of physical entropy (and dissipate much less than ''kT'' ln 2 energy to heat) for each useful logical operation that they carry out internally.

Today, the field has a substantial body of academic literature. A wide variety of reversible device concepts, [[logic gate]]s, [[electronic circuit]]s, processor architectures, [[programming language]]s, and application [[algorithm]]s have been designed and analyzed by [[physicist]]s, [[electrical engineer]]s, and [[computer scientist]]s.

This field of research awaits the detailed development of a high-quality, cost-effective, nearly reversible logic device technology, one that includes highly energy-efficient [[clocking]] and [[synchronization]] mechanisms, or avoids the need for these through asynchronous design. This sort of solid engineering progress will be needed before the large body of theoretical research on reversible computing can find practical application in enabling real computer technology to circumvent the various near-term barriers to its energy efficiency, including the von Neumann–Landauer bound. This may only be circumvented by the use of logically reversible computing, due to the [[second law of thermodynamics]].<ref>{{Cite book |last=Frank |first=Michael P. |title=Reversible Computation |chapter=Physical Foundations of Landauer's Principle |date=2018 |editor-last=Kari |editor-first=Jarkko |editor2-last=Ulidowski |editor2-first=Irek |chapter-url=https://link.springer.com/chapter/10.1007/978-3-319-99498-7_1 |series=Lecture Notes in Computer Science |volume=11106 |language=en |location=Cham |publisher=Springer International Publishing |pages=3–33 |arxiv=1901.10327 |doi=10.1007/978-3-319-99498-7_1 |isbn=978-3-319-99498-7|s2cid=52135244 }}</ref>