September 2017
Abstracts of the QSIT Lunch Seminar, Thursday, September 7, 2017
Manipulating magnetic properties in a periodically driven many-body system
Kilian Sandholzer – Quantum Optics Group (Esslinger group), ETH Zurich
Periodic driving can be used to coherently control the properties of a many-body state and to realize new phases which are not accessible in static systems. In this context, cold fermions in optical lattices provide a highly tunable platform to investigate driven many-body systems and additionally offer the prospect of quantitative comparisons to theoretical predictions.
We address the difficulties of realizing a driven interacting system by first implementing an array of double-well potentials hosting two fermionic atoms. In this model system we demonstrate how to access a desired Floquet state. Furthermore, we achieve independent control over the single particle tunneling and the magnetic exchange energy by driving near-resonantly to the interaction. Using this approach on a 3D hexagonal lattice enables us to show that anti-ferromagnetic correlations in a fermionic many-body system can be enhanced or even switched to ferromagnetic ordering.
On the zeroth law of thermodynamics
Philipp Kammerlander – Quantum Information Theory (Renner group), ETH Zurich
We introduce a new operational mathematical framework for classical phenomenological thermodynamics inspired by (quantum) information theory. By formulating a minimal set of operational assumptions we are able to rederive the theory’s statements along standard lines not referring to ambiguous terms. While doing so, we prove a central theorem of phenomenological thermodynamics, Carnot's theorem on the effciency of classical reversible cyclic thermal machines. We follow the standard proof of Carnot's theorem and, interestingly enough, do not have to refer to the 0th law of thermodynamics in the course of doing so. This is surprising given the fact that to our knowledge all standard proofs do. (The 0th law states that the relation among two systems `being in thermal equilibrium relative to each other' is an equivalence relation.)
In this talk I will focus on the specific findings which question the status of the thought-to-be fundamental 0th law in the standard derivation of thermodynamics as it is often encountered in textbooks and undergraduate courses.