Karen Wintersperger

PhD Student

Ludwig-Maximilians-Universität München

Schellingstr. 4

80799 München


What fascinates me about my work is the great degree of control we have over the experimental parameters enabling the direct measurement of abstract theoretical concepts.


I am doing my PhD at LMU in the group of Immanuel Bloch. We are investigating ultracold atoms in an optical honeycomb lattice to simulate new phases of matter which are otherwise difficult to observe in conventional solid state systems.


Realization of an anomalous Floquet topological system with ultracold atoms

K. Wintersperger, C. Braun, F. Nur Ünal, A. Eckardt, M. Di Liberto, N. Goldman, I. Bloch, M. Aidelsburger

Nature Physics (2020).

Show Abstract

Coherent control via periodic modulation, also known as Floquet engineering, has emerged as a powerful experimental method for the realization of novel quantum systems with exotic properties. In particular, it has been employed to study topological phenomena in a variety of different platforms. In driven systems, the topological properties of the quasienergy bands can often be determined by standard topological invariants, such as Chern numbers, which are commonly used in static systems. However, due to the periodic nature of the quasienergy spectrum, this topological description is incomplete and new invariants are required to fully capture the topological properties of these driven settings. Most prominently, there are two-dimensional anomalous Floquet systems that exhibit robust chiral edge modes, despite all Chern numbers being equal to zero. Here we realize such a system with bosonic atoms in a periodically driven honeycomb lattice and infer the complete set of topological invariants from energy gap measurements and local Hall deflections.

DOI: 10.1038/s41567-020-0949-y

Parametric Instabilities of Interacting Bosons in Periodically Driven 1D Optical Lattices

K. Wintersperger, M. Bukov, J. Näger, S. Lellouch, E. Demler, U. Schneider, I. Bloch, N. Goldman, M. Aidelsburger

Physical Review X 10, 011030 (2020).

Show Abstract

Periodically driven quantum systems are currently explored in view of realizing novel many-body phases of matter. This approach is particularly promising in gases of ultracold atoms, where sophisticated shaking protocols can be realized and interparticle interactions are well controlled. The combination of interactions and time-periodic driving, however, often leads to uncontrollable heating and instabilities, potentially preventing practical applications of Floquet engineering in large many-body quantum systems. In this work, we experimentally identify the existence of parametric instabilities in weakly interacting Bose-Einstein condensates in strongly driven optical lattices through momentum-resolved measurements, in line with theoretical predictions. Parametric instabilities can trigger the destruction of weakly interacting Bose-Einstein condensates through the rapid growth of collective excitations, in particular in systems with weak harmonic confinement transverse to the lattice axis. Understanding the onset of parametric instabilities in driven quantum matter is crucial for determining optimal conditions for the engineering of modulation-induced many-body systems.


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