A classical simulation of quantum systems demands enormous computational resources. The dimension of underlying Hilbert space scales exponentially with the number of participating elements (N), requiring a 2(2N) size of calculation matrix for a unitary operation, for example, 2(100) approximate to 10(30) for only N = 50. With the increase of N, the first obstacle to encounter is in fact the deficiency of computer memories. A straightforward resolution is to use a quantum computer, a calculating device that operates with the principle of quantum mechanics. During the last twenty years, quantum computing once considered as theoretical exercise has become an important field of research in modern physics. At the forefront of quantum information technology, quantum computing has emerged as a new engineering field with broad interest not only in physics but also in computer science, electronics engineering, and mathematics.