Application Of Dynamical Decoupling In Suppressing The Next-nearest-neighbor Interactions

Quantum information science is an interdiscipline of quantum mechanics and information science,it contains quantum simulation,quantum computing,quantum sensing,quantum communication and quantum cryptography and so on.Due to its quantum properties,quantum information science performs better than classical information science in many aspects,such as a faster computational speed.What is more,quantum computing can solve some problems that the classical computing can not.This thesis introduces the basic knowledge of quantum information science,such as qubits,quantum logic gates,and quantum entanglement.By now,in pushing quantum information science to reality,there are still some difficulties,for example,the generation of the initial state,the measurement of the final state and overcoming the decoherence.Because of these difficulties,people are committed to overcoming these obstacles to realize the practical application of quantum information science in our daily life.The research on how to effectively overcome quantum decoherence is interesting.There are three common methods on how to overcome quantum decoherence,namely quantum error correction code,decoherence-free subspace and quantum dynamical decoupling.This thesis focuses on the third one.There are two important methods for dynamical decoupling,one is periodic dynamical decoupling(PDD)and the other is Uhrig dynamical decoupling(UDD).When preparing the cluster states in the XY model of the Heisenberg interactions,both PDD and UDD can effectively eliminate the unwanted next-nearest-neighbor interactions,while the effet of UDD is better than that of PDD.The details are as follows:The cluster states can be generated for quantum computing in the spin chain with XY interactions by two step operations.Up to now,most of the schemes of generating cluster states only are considered the nearest-neighbor interactions between the spins with ignoring the nextnearest-neighbor interactions.The fidelity of the generated cluster states becomes smaller and smaller with the increase of the spin number when the next-nearest-neighbor interactions are taken into account.The research shows that the periodic dynamical decoupling could effectively suppress the noise of next-nearest-neighbor interactions.Generally,UDD performs better than PDD on noise suppressing.The scheme of eliminating the next-nearest-neighbor interactions with UDD is provided,the results show that the fidelity of cluster states with UDD is bigger than that of PDD when the number of applied pulse is the same,that is to say,UDD is better than PDD for suppressing next-nearest-neighbor interactions in XY model.