Talk:Quantum dot cellular automaton

Removed misleading paragraph
This is wrong:
 * The term “Quantum Computer” does not refer to a computer employing a specific technology but to any kind of system that can perform computation making direct use of any distinctively quantum mechanical phenomena, regardless of its materials and implementation method. A handful of quantum technologies exist today. Rapid Single Flux Quantum (RSFQ) logic, Resonant Tunneling Device (RTD) logic, Single Electron Transistor (SET) logic, and Spin Transistor Logic (STL) are among the most popular emerging quantum computing technologies . The type of quantum technology discussed here is Quantum Cellular Automata (QCA).

This paragraph is based on a natural but incorrect interpretation of the term “Quantum Computer”. This term refers to machines that would use quantum entanglement to perform operations in ways inaccessible to classical computers -- a category which includes not just transistor-based machines, but all the computing schemes listed here. Quantum dot cellular automata are also classical in this sense.

Removed off-topic paragraphs
The following paragraphs and figure describe an irrelevant automaton and speculations by Steve Wolfram. If they contribute anything, they should do so in the appropriate articles, not here:

''The concept of Cellular Automata (CA), along with its practical applications, has certainly increased in popularity over the last three decades. It is a relatively new concept that was first proposed to study crystal growth in the 1940’s. A cellular automaton is an abstract system consisting of a uniform (finite or infinite) grid of cells. Each one of these cells can only be in one of a finite number of states at a discrete time. The state of each cell in this grid is determined by the state of its adjacent cells, also called the cell’s “neighborhood”. The most popular example of a cellular automaton was presented by John Horton Conway in 1972. He named it “The Game of Life”. He proposed a grid in which individual cells can either be dead or alive, depending on the state of their direct neighbors. The game consists of three very simple rules. If a living cell has less than two living neighbors, it will die in the next generation as if by loneliness. If a living cell has more than three living neighbors, it will die as if by overpopulation. Finally, if a dead cell has exactly three neighbors, it will live in the next generation as if by reproduction. Figure 1 shows several segments of a CA grid in order to observe the behavior that the center cell exhibits under different conditions. The first column represents the current state of the automaton and the second column represents its future state. The rows represent several grid segments.'' Figure 1 - Example of a cellular automaton.

''The importance of CA lies on the ability to study and predict behaviors of any kind of phenomena by modeling element interactions through simple rules. One of the most recent and significant publications on Cellular Automata is the book “A New Kind of Science”. Stephen Wolfram, the author of the book, studies the possibility of replacing physics as we know it with what he calls “a truly fundamental model”.''

''“Just over twenty years ago I made what at first seemed like a small discovery: a computer experiment of mine showed something I did not expect. But the more I investigated, the more I realized that what I had seen was the beginning of a crack in the very foundations of existing science, and a first clue towards a whole new kind of science.” 4 – Stephen Wolfram''

''He argues CA is not just the means to a model, but probably the basis for behavior in all of our universe’s phenomena. Although analyzing the validity and originality of these ideas is outside the scope of this Wikipedia entry, it is sufficient to consider that for some, CA is not merely another way of modeling phenomena, but a potential replacement solution to avoid the limitations of current physics models and mathematics. For now, it will be important to remember that all CA are discrete in time, location and state.'' —The preceding unsigned comment was added by Harold f (talk • contribs) 03:56, 2 May 2007 (UTC).

adding to physics wikiproject
This article doesn't have a wikiproject, so I propose adding it to the physics wikiproject. It seems to fit better with the scope of physics than the computing wikiproject. For my initial assessment, I think this article would have "low" importance and a "B" class. This topic seems to be a bit advanced: I imagine that it would be taught in the upper undergraduate or graduate level, hence the "low" importance (only of interest to specialists). This article seems to be well written with many diagrams and references, and the scope covers a lot about this topic, so I think this article would merit a "B" class. I don't think it would be a GA yet, since the article is a bit difficult to understand for a non-expert.

As a side note, I'm going to add a "cleanup-jargon" tag - there are instances where I can't tell if phrases are technical terms or not. For example, are "distinguishability", "conditinal change of state", and "barriers" technical terms? How does the quantum dot pattern become a "plus-sign"? What is fully implied by "wire-crossing," besides the wire in fig.4 crossing with another wire: why is it a fundamental implementation problem? Lisatwo 16:31, 22 July 2007 (UTC)

Restructure
This article is almost completely dominated by discussion of Quantum Dot Cells, which seems to be a single specific proposal for implementing cellular automata using quantum phenomena. This is unfortunate for people who might visit this page to find out about computational models of QCA, such as the Watrous model, the Schumacher-Werner model , or the model recently proposed by Perez-Delgado and Cheung.

I think that, ideally, Quantum Dot Cells would warrant it's own page, which would be linked to from the Quantum Cellular Automata page as one proposed scheme for implemntation. Alternatively, the main article could enumerate the different theoretical models and proposed schemes for implementation (each of which would have its' own page), with a very brief account of each.

Does anyone have any counterpoints? What would be the best way to resolve this? Infinigesimal 19:19, 8 September 2007 (UTC)


 * A follow-up: I have written a short new article on quantum cellular automata, and have renamed the current article to "quantum dot cellular automata", which is the less-ambiguous (and quite common) term for the subject of this article. Infinigesimal 09:02, 16 September 2007 (UTC)

Tone editing
I'm editing a lot of this article for tone--it must be remembered that Wikipedia is neither a textbook nor an academic journal. Thus, we present facts, but don't make claims like "It must be remembered that..." or "As stated before..." or "Now we turn to..." A simple factual summary of information provided in reliable sources is the appropriate style. Qwyrxian (talk) 01:03, 25 February 2011 (UTC)

Problems with figures
Figures 4, 6, and 8 have problems, which I have tried to compensate for by adding notations to their captions. Figure 4 appears to show the distance between cells to be much smaller than the distance between dots, whereas the reverse is true. Figure 6 shares the problem of Figure 4 and also flips the logical values associated with the two polarizations states from the values shown in Figure 3 (which is asserted in the text to be "standard"). Figure 8 shares the problem of Figure 4 and also shows the distance between dots in the vertical wire to be smaller than that in the horizontal wire, despite the text asserting that they are the same. It seems that it is common in such diagrams to represent the vertical wire cells as dots at the corners of diamond shapes (squares turned 45 degrees) instead of dots at the sides of squares which are orthogonal to the horizontal wire cells. For compactness, Figure 4 might go unchanged (keeping the cautionary scale notation); Figure 6 should be corrected, which is an easy change; Figure 8 probably needs to be reworked to be more accurate, clear, and possibly in keeping with standard diagrams. Can someone make new figures? Ontyx (talk) 12:51, 12 July 2012 (UTC)