Sequential resonant tunneling in quantum cascade lasers

A model of sequential resonant tunneling transport between two-dimensional subbands that takes into account explicitly elastic scattering is investigated. It is compared to transport measurements performed on quantum cascade lasers where resonant tunneling processes are known to be dominating. Excellent agreement is found between experiment and theory over a large range of current, temperature and device structures

Experimental realization of a momentum-space quantum walk

We report on a discrete-time quantum walk that uses the momentum of ultra-cold rubidium-87 atoms as the walk space and two internal atomic states as the coin degree of freedom. Each step of the walk consists of a coin toss (a microwave pulse) followed by a unitary shift operator (a resonant ratchet pulse). We carry out a comprehensive experimental study on the effects of various parameters, including the strength of the shift operation, coin parameters, noise, and initialization of the system on the behavior of the walk. The walk dynamics can be well controlled in our experiment; potential applications include atom interferometry and engineering asymmetric walks.Comment: 11 pages, 11 figure

Guaranteed efficient energy estimation of quantum many-body Hamiltonians using ShadowGrouping

Estimation of the energy of quantum many-body systems is a paradigmatic task in various research fields. In particular, efficient energy estimation may be crucial in achieving a quantum advantage for a practically relevant problem. For instance, the measurement effort poses a critical bottleneck for variational quantum algorithms. We aim to find the optimal strategy with single-qubit measurements that yields the highest provable accuracy given a total measurement budget. As a central tool, we establish new tail bounds for empirical estimators of the energy. They are helpful for identifying measurement settings that improve the energy estimate the most. This task constitutes an NP-hard problem. However, we are able to circumvent this bottleneck and use the tail bounds to develop a practical, efficient estimation strategy, which we call ShadowGrouping. As the name suggests, it combines shadow estimation methods with grouping strategies for Pauli strings. In numerical experiments, we demonstrate that ShadowGrouping outperforms state-of-the-art methods in estimating the electronic ground-state energies of various small molecules, both in provable and practical accuracy benchmarks. Hence, this work provides a promising way, e.g., to tackle the measurement bottleneck associated with quantum many-body Hamiltonians.Comment: 14+6 pages, 5+0 figures. v2: revisions in structure of main text and addition of the schematic figure 1. Presented at TQC 202

Quantum Walks of kicked Bose-Einstein condensates

We analytically investigate the recently proposed and implemented discrete-time quantum walk based on kicked ultra-cold atoms. We show how the internal level structure of the kicked atoms leads to the emergence of a relative light-shift phase immediately relevant for the experimental realization. Analytical solutions are provided for the momentum distribution for both the case of quantum resonance and the near-resonant quasimomenta.Comment: 28 page draft, comments welcom

Umwelt und Entwicklung Beiträge der Privatwirtschaft insbesondere im Bereich der Umwelt- und Raumplanung

Einleitung In diesem Artikel geht es darum, darzustellen, welche Probleme sich im Umweltbereich in den Ländern der Dritten Welt stellen und welche Beiträge Schweizer Ingenieure und Berater zur Lösung dieser Probleme leisten können. Die Ausführungen dienen dem Anliegen dieser Schrift, die bestehenden Aussenbeziehungen unseres Landes sichtbar zu machen und Hinweise auf mögliche weitere Aufgabenfelder zu geben. Problemstellungen in der Dritten Welt Um das Wesentliche nicht aus den Augen zu verli..

Umwelt und Entwicklung Beiträge der Privatwirtschaft insbesondere im Bereich der Umwelt- und Raumplanung

Einleitung In diesem Artikel geht es darum, darzustellen, welche Probleme sich im Umweltbereich in den Ländern der Dritten Welt stellen und welche Beiträge Schweizer Ingenieure und Berater zur Lösung dieser Probleme leisten können. Die Ausführungen dienen dem Anliegen dieser Schrift, die bestehenden Aussenbeziehungen unseres Landes sichtbar zu machen und Hinweise auf mögliche weitere Aufgabenfelder zu geben. Problemstellungen in der Dritten Welt Um das Wesentliche nicht aus den Augen zu verli..