View source for Well merging

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[[File:Principles of Adiabatic Processes powerpoint ppt presentation Slide29 Possible Adiabatic Transitions.png|400px|thumb|right|Red arrows are lossy/dissipative/irreversible well merging processes. Follow the spiral of green arrows to go from a 0 to a 1 (or vice versa) in a lossless/nondissipative/reversible/adiabatic manner.]]

[[File:Reversible_mechanosynthesis_annotated.svg|400px|thumb|right|By smartly crafting the temporal trajectory of the potential wells for tool-tip and work-piece-surface mechanosynthesis can be made vastly more efficient than "normal chemistry".]]

This page is about …
* … energetic losses being incurred when potential energy wells of a bi-stable system are merged. <br>
* … changing the state of a system without needing to expend energy (in the limit of slow speeds). <br>

== Contexts ==

=== Logic / computation ===

Changing bits from 0 to 1 or vice versa losslessly in [[reversible logic]] <br> 
possibly [[nanomechanical computation]] like e.g. [[rod logic]]. <br>

=== Building & Energy ===

Depositong an atom from a tooltip to a workpiece losslessly.<br>
Breaking and forming chemical bonds losslessly in a [[chemomechanical converter]] system. <br>

== The basic process to avoid well merging ==

'''Green arrows in graphic.'''

'''(1) While the barrier is still up''' <br>
– Bring the occupied state in an energetic favorable <br>
– Bring the unoccupied state in an energetic infavorable state <br>

'''(2) Remove the barrier''' <br>
– either bringing the wells closer together if a space of vacuum is the barrier (mechanosynthesis)<br>
– or removing/retract a physical part responsible for the barrier (reversible logic)<br>
This process may recuperate energy back into storage. <br>
With absence of a barrier now an intermediate state is occupied. <br>

'''(3) While the barrier is still down''' <br>
– Bring the eventually to be occupied state in an energetic favorable <br>
– Bring the eventually to be unoccupied state in an energetic infavorable state <br>

'''(4) Raise the barrier''' <br>
By doing step (2) in reverse. <br>
Now the occupied state switched the well. <br>

The barrier needs to be >>kT to prevent thermally caused flips. <br>
Note that at no point there was this >>kT energy dissipated. <br>
This would have happened if the barrier would have been removed <br>
during a phase where the occupied state is in an well that is energetically unfavorable (or even equally favorable). <br>

== Well merging ==

'''The red arrows in the graphic shows these adiabatic process violations.''' <br>
All these lead to irreversible energy dissipation. <br>
This energy dissipative process is called '''"well merging"'''. <br>

In computation some times it is much more practically to strategically delete a few bits <br>
by well merging rather than trying to keep absolutely everything reversible. <br>
Fascinatingly if fully reversible logic would be exactly as powerful as irreversible logic then <br>
cryptography based on asymmetric problem difficulty would be kind of broken. <br>
See: [[Reversible logic]]

== Limits to losslessness ==

Of course this is all merely near losslessly. <br>
As there are are other dissipation mechanisms like dynamic friction <br>
and dissipation pertaining to reciprocative motions. <br>
Plus there is an absolute minimum amount to dissipate to define a local arrow of time for the nanomachinery. <br>
Preventing it from running backwards occasionally.

== Remaining dissipation in the adiabatic case ==

Regarding the absolute minimum energy needed for a system to operate forward at finite nonzero speeds: <br> 
This is a matter of dissipating enough energy per time to gain a sufficiently defined [[arrow of time]]. <br>
In the context of [[chemomechanical converter]]s, [[mechanochemistry]] and [[mechanosynthesis]] <br>
a way to get down to the absolute minimum mandatory amount of energy dissipation may be <br>
there process defined on the page '''[[dissipation sharing]]'''.

== Related ==

* [[Reversible logic]]
* [[Piezomechanosynthesis]] & [[Chemomechanical converter]]
----
* [[Arrow of time]]
* [[Dissipation sharing]]