Decoherence and disentanglement due to classical noise.

摘要

In this thesis, we study the decoherence and disentanglement processes of generic quantum two level systems (qubits) in the presence of classical random telegraph noise.;When the environment is modeled as an ensemble of random telegraph noise sources, the decoherence problem of a qubit subject to broad spectrum noise can be addressed. We analyze experimental data on different types of pulsed signals in superconducting flux qubits. The physical parameters in the model can be extracted from data fitting and we find signatures of 1/f noise. For multi-qubit systems, we study the disentanglement process of two non-interacting qubits in the presence of uncorrelated random telegraph noise sources, and find the entanglement evolution can take various different forms. Generalizations to interacting qubits and correlated noises are also discussed.;To better understand the origin of different entanglement evolutions for general decoherence processes, we characterize the state space of qubits using a geometric picture known as the generalized Bloch vector representation of the density matrix. Based on model studies, we propose four topological categories for entanglement evolution and relate them to certain properties of the decoherence model. Here we mainly focus on two-qubit systems. Generalizations to N-qubit systems are also discussed.;Finally, we investigate the effectiveness of quantum error correction in the presence of temporal and spacial noise correlations. The three qubits repetition code is examined given two dephasing noise models: the environment is modeled as classical random telegraph noise in one case and quantum mechanical bosonic fields in the other case. The fidelity in the short time expansion is independent of the noise correlation in one model but not the other. The origin and indication of this behavior are discussed.