Turing Machines, logic gates and computers

Computers are physical objects, and computations are physical processes. What computers can or 

Besides using computers to help in their research, what are the possible interests of physicists in computers and computational processes Even this question could lead to different routes. Researchers could, for instance, attack on the material science side, studying the physical properties of bulk semiconductor materials, the basic stuff from which chips are made of, or studying the magnetic materials, the basic stuff hard-discs are built from. One could take the route of the so-called nanoscience and nanotechnology and exploit the ultimate limits of miniaturization of computer components, down to the molecular size. Yet, we can take an entirely different route, and ask for very fundamental questions about computers and about computation. One could ask, for instance, what is the minimum amount of energy and time necessary to flip a bit of information, or whether it is possible to perform computation without any energy expenditure at all. Or still, what is the limit 

what is a computer There seems to be no single answer to this question. The answer you give depends on the way you look at a computer, or actually, the way you see the world. Quantum computation (QC) and quantum information processing (QIP) appeared from considerations about the very basic physical processes of computation. 

However interesting may be, QC and QIP would be restricted to a bunch of mathematical results if there was no way to implement them in the physical world, as much as a Turing Machine (see below) would be a mere theoretical curiosity without the existence of computers This book deals with a particular way to implement QC and QIP it is called Nuclear Magnetic Resonance, or simply NMR. There are excellent books in the subjects of quantum computation and quantum information [6,7], in NMR [8] and in (classical) computation [9]. This book exploits elements of these three different fields, and put them together in order we can understand NMR-QIP. In this chapter we will introduce the basic elements of computation, and will discuss the physics of computational processes. Chapters 2 and 3 introduce the necessary background of NMR and quantum computation theories, in order we can exploit the realizations of NMR-QIP in the subsequent chapters. 

Any Turing Machine is composed by the following basic ingredients  

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