Decoherence in quantum systems

Henry Crumley

This paper studies the energy decoherence of an interacting quantum system. It first reviews the experiments that motivated the postulates of quantum mechanics. It then discusses a decoherence that occurs dynamically in a closed system. This effect is studied in interacting quantum systems consisting of an oscillator and spins using analytical and numerical methods. The subsequent results are contrasted with cases with no decoherence. Connections of energy decoherence with thermodynamics are explored.

Walter T. Strunz

Mario Castagnino, Roberto Laura, Olímpia Lombardi

A generalized formal framework for decoherence, that can be used both in open and closed quantum systems, is sketched. In this context, the relationship between the decoherence of a closed system and the decoherence of its subsystems is studied, and the corresponding decoherence times are defined: for macroscopic systems, the decoherence time of the closed system is much greater than the decoherence time of its subsystems. Finally, it is shown that the application of the new formal framework to a well-known model leads to physically adequate results.

Jurjen F. Koksma, Tomislav Prokopec, Michael G. Schmidt

Mohd Shoaib Qureshi, Tabish Qureshi

Quantum decoherence refers to the phenomenon when the interaction of a quantum system with its environment results in the degradation of quantum coherence. Decoherence is considered to be the most popular mechanism responsible for the emergence of classicality from quantum mechanics. The issue of formulating a measure of decoherence is addressed here. The approach taken here is that decoherence results from the entanglement of a quantum system with certain environment degrees of freedom, and quantifying this entanglement should yield the most natural measure of decoherence. A simple measure of decoherence is presented based on this notion, and it is examined for various example systems. The measure proves to be effective and is relatively straightforward to compute. In addition, a method has been proposed to measure decoherence in a Mach-Zehnder interferometer which may be useful in neutron interferometry.

Maja Katarina Berglund

When a quantum mechanical system interacts with its environment, the system and its environment can become entangled. This entanglement suppresses the interference effects between thedifferent states of the system. Thus, the system behaves more like a statistical mixture of statesrather than a superposition of states.Within quantum technologies, one aims to make use of a systems quantum mechanical properties. Thus, in the development of quantum technologies, it is important to get a better understanding of decoherence and how to prevent it. Furthermore, the decoherence effect due to quantumentanglement between a quantum system and its environment is often neglected in Materials Science. It is therefore important to determine if there are cases when the degree of decoherence is sohigh that it is not negligible.This project studies the variation of the degree of decoherence in a praseodymium-like modelsystem. The purpose of the project is to get a deeper understanding of which parameters of thesystem have a large impact on the degree of decoherence and why.The results show that there are many combinations of parameters where the degree of decoherence is significant. The results also show that certain parameters have a greater impact on thedegree of decoherence than others.It is important to note that certain approximations and restrictions have been used during theconstruction of the model system that may have made the model system less realistic.