Abstarct: The progressive development of science and human needs makes an obligation to expedite technology. Computers and calculating machines are everlasting human needs involved in his mind, so that engineers and scientists often try to offer more advanced ones. The applications of quantum mechanics in industry make scientists to make advantage of particular quantum properties in development of computers. In this manner computers can be optimized in a way which is incomparable with our classical computers. The above mentioned needs cause the increasing research in application of quantum mechanics for computers. Here we try to clear some aspects of quantum computers from physics point of view. The information theory plays the fundamental rule in both classical and quantum computers. In chapter one of this thesis, the connection of information theory with physical concepts especially work and energy is discussed. Chapter two is devoted to classical information theory, especially Shannon information and its important features in classical computers. In chapter three quantum information theory and von Neumann entropy as the most effective relation are discussed. It also includes some applications of von Neumann entropy. In chapter four some suggestions are offered to develop the quantification of information in quantum computers. Furthermore some supposed relations have been compared with von Neumann entropy. At the last sections of chapter four, the development and obvious better performance three –states systems in compared with two –states ones and also the profits of three states usages are discussed.