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Added a reference for that quantum computers are reversible as long as they do not measure/collapse the quantum states they operate on. Same ref could also be used for the general statement about quantum mechanics in physical reversibility section, since .. well. derp |
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'''Reversible computing''' is any [[model of computation]] where the [[computational process]], to some extent, is [[time-reversible]]. In a model of computation that uses [[deterministic]] [[State transition system|transitions]] from one state of the abstract machine to another, a necessary condition for reversibility is that the [[Binary relation|relation]] of the [[Map (mathematics)|mapping]] from states to their successors must be [[injective function|one-to-one]]. Reversible computing is a form of [[unconventional computing]].
Due to the [[Unitarity (physics)|unitarity]] of [[quantum mechanics]], [[quantum circuit]]s are reversible, as long as they do not "[[
==Reversibility<!--'Logical reversibility', 'Charge recovery logic', and 'Adiabatic computing' redirect here-->==
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==Physical reversibility==
Landauer's principle (and indeed, the [[second law of thermodynamics]] itself) 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 name="Williams"/>
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 we can accumulate a negligible total amount of uncertainty regarding the complete physical state of the mechanism, per each logic operation that is performed. In other words, we would need to precisely track the state of the active energy that is involved in carrying out computational operations within the machine, and design the machine in such a way 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.
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