Description and control of decoherence in quantum bit systems

Gutmann, Henryk (2005): Description and control of decoherence in quantum bit systems. Dissertation, LMU München: Faculty of Physics

Abstract

The description and control of decoherence of quantum bit systems have become a field of increasing interest during the last decade. We discuss different techniques to estimate and model decoherence sources of solid state quantum bit realizations. At first, we derive a microscopic, perturbation theoretical approach for Lindblad master equations of a spin-Boson model at low temperatures. A different sort of decoherence is investigate by means of the bistable fluctuator model. For this particular but nevertheless for solid state qubits relevant noise source, we present a suitably designed dynamical decoupling method (so-called quantum bang-bang). This works as a high-pass filter, suppressing low frequency parts of the noise most effectively and thus being a promising method to compensate the ubiquituous 1/f noise. Furthermore, we investigate the behaviour of a two coupled spin system exposed to collective and localized bath. For this dressed-spin system we receive by means of scaling-analysis in first order a quantum phase diagram. On that we can identify the various quantum dynamical and entanglement phases.

• Item Type: Theses (Dissertation, LMU Munich)
• Keywords: low-temperature Lindblad equation, bistable fluctuator, 1/f noise, bangbang decoupling, quantum phase diagram
• Subjects: 500 Natural sciences and mathematics; 500 Natural sciences and mathematics > 530 Physics
• Faculties: Faculty of Physics
• Language: English
• Date of oral examination: 3. August 2005
• 1. Referee: Wilhelm-Mauch, Frank
• Signature of the printed copy: 0001/UMC 14743