June 2014
Abstracts of the QSIT Lunch Seminar, Thursday June 5, 2014
Boundary between the Thermal and Statistical Polarization Regimes in a Nanometer-scale Spin Ensemble
Benedikt Herzog, Spin, Quantum Electronics, Nanomechanics - Poggio Lab, University of Basel
As the number of spins in an ensemble is reduced, the statistical fluctuations in its polarization eventually exceed the mean thermal polarization. This transition has now been surpassed in a number of recent nuclear magnetic resonance experiments, which achieve nanometer-scale detection volumes. Most recently, we measured nanometer-scale ensembles of nuclear spins in a KPF6 sample using magnetic resonance force microscopy.In particular, we investigated the transition between a regime dominated by thermal and statistical nuclear polarization. The ratio between the two types of polarization provides a precise measure of the number of spins in the detected ensemble.
Entropies in thermodynamics and information theory: a new approach
Lea Krämer, Quantum Information Theory, ITP, ETH Zurich
The concept of entropy was introduced independently in thermodynamics and in statistical mechanics - as such, it is surprising that those definitions should coincide. Apart from consistence and similarity, the step of identifying the two properties lacks conceptual justification. In this talk, I will give a brief introduction that outlines this problem. I will then present new work in this direction, based on an axiomatic approach to entropy within phenomenological thermodynamics by Lieb & Yngvason. I will show how the axiomatic approach can be carried over to a microscopic framework within the context of resource theories. We may then link equilibrium and out-of-equilibrium entropy in thermodynamics to corresponding quantities in information theory, in particular in a single-shot setting. I will also mention further applications of this framework to different physical scenarios, like a thermodynamic system coupled to various kinds of reservoirs. We will see how quantities like the free energy emerge from the framework.