In recent years, the study of quantum information processing has attracted more and more interest.In this field, the unique quantum mechanical features such as entanglement and superposition opens new horizons for computations.The massive parallelism of quantum computer allows one to manipulate simultaneously, exponentially many states, thus performing computational tasks faster than its classical counterpart.The most known example is provided by the problem of factoring large integers which can be solved with exponential efficiency by Shors algorithm[1].Another famous example is the Grover algorithm which significantly accelerates the problem of searching an unsorted database[2].