Some Theoretical Studies of Disordered Quantum Systems.

T Schulte, S. Drenkelforth, J. Kruse +6 more

Disorder plays a crucial role in many systems particularly in solid state physics. However, the disorder in a particular system cannot usually be chosen or controlled. We show that the unique control available for ultracold atomic gases may be used for the production and observation of disordered quantum degenerate gases. A detailed analysis of localization effects for two possible realizations of a disordered potential is presented. In a theoretical analysis, clear localization effects are observed when a superlattice is used to provide a quasiperiodic disorder. The effects of localization are analysed by investigating the superfluid fraction and the localization length within the system. The theoretical analysis in this paper paves a clear path for the future observation of Anderson-like localization in disordered quantum gases.

Massimiliano Giona

David A. Evensky

Max Marcus

Quantum process tomography might be the most important paradigm shift which has yet to be translated fully into theoretical chemistry. Its fundamental strength, long established in quantum information science, offers a wealth of information about quantum dynamic processes which lie at the heart of many (if not all) chemical processes. However, due to its complexity its application to real chemical systems is currently beyond experimental reach. Furthermore, it is susceptible to errors due to experimental and theoretical inaccuracies and disorder has long been thought to be an obstacle in its applicability. Here, I present the first results of a study into the use of quantum light for quantum process tomography. By using a toy model and comparing numerical simulations to theoretical predictions the possible enhancement of using non-conventional light is studied. It is found, however, that disorder is necessary make the use of quantum light suitable for process tomography and that, in contrast to conventional wisdom, disorder can make the results more accurate than in an ordered system.

Jian Wang

Disorders and dissipations play the key role in the understanding of quantum coherent system. In this thesis, I'm using numeric method plus theoretical analysis to answer the questions: What are the low energy modes in disordered quantum spin system? How will environment dissipation damp the spin system's quasi-particle excitation quantitatively? There are three parts in my thesis. Part 1 is the study of disordered quantum Ising chain. Part 2 is a numerical method for analytic continuation. Part 3 is the study of dissipative quantum Ising chain.

Reiner Kree