Reversible gate

The question which Landauer failed to ask in 1961 [land61] and which was answered first by Bennett in 1973 [benu73] and later, independently, by Predkin [fredkiu82], is whether irreversible logic gates are essential to computation. Might it be possible to construct a universal set out of reversible gates ... 

A simple exercise should convince the reader that the set of 24 possible 2-input/ 2-output reversible gates fails to be universal. To find a universal set we must there-... 

In contrast, in the non-swollen form (pH < 6.5), there is no apparent exchange of large molecules between the cavity and the bulk medium. This transition can be viewed as analogous to reversible gating in molecular host-guest chemistry, " with the potential for se-... 

Fig. 4.5 Evaluating the timing impact of the physical synthesis transformation in Fig. 4.3 (output side only), a Bounded transactional timing analysis will not propagate the change outside of a specified window, b In the event of a reversion, gates with dirty timing wdH have their timing data...

The above photochemical reaction is irreversible. Hemicarcerands 32 and 33 only allow triggered release of encapsulated guests, but, once photolyzed, cannot be recycled. In a reversible gated hemicarcerand, switching between closed and open states is possible in both directions. Thus, target molecules can be released or trapped in response to... 

Bocharova V, Tam TK, Halamek J, Pita M, Katz E. Reversible gating controlled by enzymes at nanostmctured interface. Chem Commun 2010 46 2088-2090. 

An ideal quantum device works in a reversible way due to the unitary evolution according to the Schrodinger equation. This does not constitute a problem. It has been shown that the necessary reversibility is not an obstacle to constructing any desired computer in an efficient way Universal computation can be done by reversible gates [13-15]. No essential additional expenditure in space and time is necessary [16-18]. 

As a simple example of a quantum computer, the quantum realization of a universal, reversible gate is described in Sect. 5.2. 

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