Modularization of the multi-qubit controlled phase gate and its NMR implementation ∗

Quantum circuit network is a set of circuits that implements a certain computation task. Being at the center of the quantum circuit network, the multi-qubit controlled phase shift is one of the most important quantum gates. In this paper, we apply the method of modular structuring in classical computer architecture to quantum computer and give a recursive realization of the multiqubit phase gate. This realization of the controlled phase shift gate is convenient in realizing certain quantum algorithms. We have experimentally implemented this modularized multi-qubit controlled phase gate in a three qubit nuclear magnetic resonance (NMR) quantum system. The network is demonstrated experimentally using line selective pulses in NMR technique. The procedure has the advantage of being simple and easy to implement.