Dynamic Decoupling Quantum Control Methods

Abstract

Since the birth of quantum mechanics in the twentieth century, it has achieved great success in many ways as a fundamental theory of natural sciences. With the development of science, the combination of quantum mechanics, classical information theory, and computing technology led to the emergence of quantum information theory and quantum theory of computation. A series of topics based on quantum information technology have been proposed, and the realization of quantum computers (Feynman, 1982) is one of the important research areas. Coherence and entanglement are essential for quantum computation and quantum information processing, but decoherence destroys the coherence of the quantum superposition states in the process of evolution and results in the reduction or even the erosion of the entanglement between subsystems. In order to maintain quantum coherence, quantum error-correcting codes a dynamic coupling scheme (Viola and Lloyd, 1998) (originally known as quantum bang-bang (BB) control) were proposed. Quantum error-correcting codes and quantum error-avoiding codes need to introduce a lot of redundant information, and also add a certain symmetry assumptions between the system and the environment. Compared with these two methods, BB control does not require the introduction of redundant qubits. The BB control scheme makes use of coherent averaging effects (Haeberlen and Waugh, 1968) and uses twin-born tailored powerful pulses to average out the effect of the unwanted Hamiltonian. After the quantum dynamical decoupling scheme was proposed by Viola and Lloyd in 1998, it was used to suppress the decoherence for one qubit. In recent years, the BB control schemes for phase decoherence in thê-, V-, and Ξ-configurations in three-level atoms have been studied (Liu et al., 2005a,b), and the BB control scheme for amplitude decoherence was designed by Cao, Liu, and Bai (2008). The BB control scheme to suppress phase decoherence in a four-level atom system in the Ξ-configuration is discussed in