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A quantum cellular automata or QCA is an abstract model of quantum computation, devised in analogy to conventional models of cellular automata introduced by von Neumann. The same name may also refer to quantum dot cellular automata, which are a proposed physical implementation of "classical" cellular automata by exploiting quantum mechanical phenomena. QCA have attracted a lot of attention as a result of its extremely small feature size (at the molecular or even atomic scale) and its ultra-low power consumption, making it one candidate for replacing CMOS technology. == Usage of the term == In the context of models of computation or of physical systems, ''quantum cellular automaton'' refers to the merger of elements of both (1) the study of cellular automata in conventional computer science and (2) the study of quantum information processing. In particular, the following are features of models of quantum cellular automata: * The computation is considered to come about by parallel operation of multiple computing devices, or cells. The cells are usually taken to be identical, finite-dimensional quantum systems (e.g. each cell is a qubit). * Each cell has a neighborhood of other cells. Altogether these form a network of cells, which is usually taken to be regular (e.g. the cells are arranged as a lattice with or without periodic boundary conditions). * The evolution of all of the cells has a number of physics-like symmetries. Locality is one: the next state of a cell depends only on its current state and that of its neighbours. Homogeneity is another: the evolution acts the same everywhere, and is independent of time. * The state space of the cells, and the operations performed on them, should be motivated by principles of quantum mechanics. Another feature that is often considered important for a model of quantum cellular automata is that it should be universal for quantum computation (i.e. that it can efficiently simulate quantum Turing machines,〔.〕〔C. Pérez-Delgado and D. Cheung, "Local Unitary Quantum Cellular Automata", Phys. Rev. A 76, 032320, 2007. See also (arXiv:0709.0006 (quant-ph) )〕 some arbitrary quantum circuit〔 D.J. Shepherd, T. Franz, R.F. Werner: Universally programmable Quantum Cellular Automaton. Phys. Rev. Lett. 97, 020502 (2006) 〕 or simply all other quantum cellular automata〔P. Arrighi, R. Fargetton, Z. Wang, Intrinsically universal one-dimensional quantum cellular automata in two flavours, Fundamenta Informaticae Vol.91, No.2, pp.197-230, (2009). See also ((quant-ph) )〕〔P. Arrighi, J. Grattage, A quantum Game of Life, Proceedings of JAC 2010, Turku, December 2010. TUCS Lecture Notes 13, 31-42, (2010). See also ((quant-ph) ) and ((Companion Website) )〕). Models which have been proposed recently impose further conditions, e.g. that quantum cellular automata should be reversible and/or locally unitary, and have an easily determined global transition function from the rule for updating individual cells.〔 Recent results show that these properties can be derived axiomatically, from the symmetries of the global evolution.〔B. Schumacher and R. Werner, "Reversible quantum cellular automata", (quant-ph/0405174 )〕〔Pablo Arrighi, Vincent Nesme, Reinhard Werner, One-dimensional quantum cellular automata over finite, unbounded configurations. See also ((quant-ph) )〕〔Pablo Arrighi, Vincent Nesme, Reinhard Werner, N-dimensional quantum cellular automata. See also ((quant-ph) )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Quantum cellular automaton」の詳細全文を読む スポンサード リンク
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