A Theoretical Realization Of Quantum Circuit For Universal Quantum Coping Machine

In recent years, people have paid much attention on quantum information, which is an emerging discipline based on quantum mechanics and computer science. If information is classical, it can be accurately replicated; while in quantum information science, information can not be accurately replicated. This is one of the main differences between classical information and quantum information. In 1982, Wootters and Zurek proposed quantum no-cloning theorem, which is based on the linear effect of quantum mechanics negated the possibility to copy an unknown quantum state exactly. The output state of quantum copying machine based on the quantum no-cloning theorem depends on the input state. It works well for coping some states, but for the other states it works badly. In 1996, Buzek and Hillery proposed a universal quantum copying machine model, such a copying machine does not depend on the input state and the degree of fidelity of copies can be greatly enhanced. In this paper, we theoretically realize the quantum circuit for universal quantum coping machine. In this paper, we first introduce the concept of quantum replication and describe quantum no-cloning theorem, then a brief introduction of the two kinds of copy machines, Wootters and Zurek quantum copying machine and the universal quantum copying machine are given.In this paper we also simply describes the basis knowledge involving in quantum circuit, including the quantum bit and the quantum bit gate; quantum circuits controlled operations; how to decompose a unitary matrix into a product of multiple two-level unitary matrices; any a n-bit of two-level unitary operation can be realized by single quantum bit gate and controlled-NOT gate.The main part of this paper is to give a theoretical realization of quantum circuit for universal quantum coping machine. We start from the universal quantum copying machine model proposed by Buzek and Hillery. First of all, we calculate the unitary matrix of transformation of the copy machine. Then we decompose the unitary matrix into a product of multiple two-level unitary matrices, each of them can be realized by the quantum controlled circuit. Finally, we put these controlled circuits together and get quantum circuit expression of universal quantum copying machine.