Quantum entropy production in phase space

A fluctuation theorem for the nonequilibrium entropy production in quantum phase space is derived, which enables the consistent thermodynamic description of arbitrary quantum systems, open and closed. The new treatment naturally generalizes classical results to the quantum domain. As an illustration the harmonic oscillator dragged through a thermal bath is solved numerically. Finally, the significance of the new approach is discussed in detail, and the phase space treatment is opposed to the two time energy measurement approach.Comment: 6 pages, 2 figures; published versio

Efficiency of harmonic quantum Otto engines at maximal power

Recent experimental breakthroughs produced the first nano heat engines that have the potential to harness quantum resources. An instrumental question is how their performance measures up against the efficiency of classical engines. For single ion engines undergoing quantum Otto cycles it has been found that the efficiency at maximal power is given by the Curzon-Ahlborn efficiency. This is rather remarkable as the Curzon-Alhbron efficiency was originally derived for endoreversible Carnot cycles. Here, we analyze two examples of endoreversible Otto engines within the same conceptual framework as Curzon and Ahlborn's original treatment. We find that for endoreversible Otto cycles in classical harmonic oscillators the efficiency at maximal power is, indeed, given by the Curzon-Ahlborn efficiency. However, we also find that the efficiency of Otto engines made of quantum harmonic oscillators is significantly larger.Comment: 6 pages, 2 figure

Quantum speed limit for non-Markovian dynamics

We derive a Margolus-Levitin type bound on the minimal evolution time of an arbitrarily driven open quantum system. We express this quantum speed limit time in terms of the operator norm of the nonunitary generator of the dynamics. We apply these results to the damped Jaynes-Cummings model and demonstrate that the corresponding bound is tight. We further show that non-Markovian effects can speed up quantum evolution and therefore lead to a smaller quantum speed limit time.Comment: 5 pages, 2 figures; Corrected inconsistency in the derivation; improved bound

Participatory empirical research on water and sanitation demand in central northern Namibia: a method for technology development with a user perspective

Improvements in water infrastructure in developing countries are of major importance for achieving access to clean water. CuveWaters, a research based IWRM project, currently underway in Namibia, is testing different technical options to de-centralise water supply and upgrade sanitation. The Cuvelai Basin is affected by highly variable precipitation, mostly saline groundwater and a lack of perennial rivers. Water management is characterised by strong dependency on a water pipeline. Finding ways to improve the situation calls for a good grasp of the local situation regarding water utilisation patterns. Technologically sophisticated concepts can easily clash with users’ socio-cultural needs and everyday behaviour as well as their understanding of planning and maintenance. A demand-responsive approach has therefore been developed. It combines a qualitative socio-empirical perspective with participatory planning. This paper discusses method development, empirical application and results. The approaches aim is to support mutual learning as a basis for a sustainable change process