January 2014

Abstracts of the QSIT Lunch Seminar, Jan 23, 2014

Nonlocality, W-states and quantum asymmetry

Gilles Puetz, GAP-Quantique, Université de Genève
Tomer Barnea, GAP-Quantique, Université de Genève

We will briefly remind the audience of the concepts of nonlocality and Bell inequalities. Having introduced these tools the remaining part of the talk will focus on a few specific questions related to these topics. In a first part we will study the properties of multipartite states, especially their behaviour under losses. More specific the nonlocality of W states where a certain number of parties were lost will be addressed. The second will evolve will include the definition of quantum asymmetry and evolve around this notion. In particular the differences between symmetric and asymmetric Bell inequality violations and possible implications thereof will be discussed.

Locally induced Aharonov-Bohm effect in scanning gate experiments

Aleksey Kozikov, Nanophysics Group, ETH Zurich

Semiconductor nanostructures are usually defined electrostatically. In order to do this, biased lateral gates or self-assembled systems can be used. The potential landscape of such nanostructures is only weakly tunable. Scanning gate microscopy provides more advanced control over the potential compared to conventional transport experiments. In this technique the conductive tip of a scanning force microscope induces a local potential. Variable strength and gradient of the tip-induced potential allows tailoring the potential landscape of nanostructures. In this work we demonstrate how to alter the potential landscape in a ballistic stadium using a scanning gate. We perform conductance measurements of the structure as a function of tip position and observe regular fringes covering the entire stadium. The fringes correspond to transmitted modes in constrictions formed between the tip-induced potential and the boundaries of the stadium. Counting the fringes gives us control over the transmission of these constrictions. We use this control to form a quantum ring and set a specific number of modes in each arm. Low-field magnetoconductance measurements of this ring show the Aharonov-Bohm oscillations.