Research topics

Thanks to modern technology it is nowadays possible to fabricate structures on the size of a few nanometers. In other words, thousands of these nanostructure fit into the diameter of single hair! For the dynamics of the particles in such structures a picosecond, which is a millionth of a millionth of a second, already feels like ages. In contrast to what we experience in everyday life, on these extreme scale new effects come into play, because everything is governed by the rules of quantum mechanics. These effects can be explored using laser pulses, which can also be used to control the dynamics in these system. To understand the new phenomena, a theoretical description and numerical modelling is required, which is the basis of our work.

We consider on the one hand nanostructures made of semiconductors, mostly semiconductor quantum dots, and on the other hand metallic structures, which act as antennas for visible light. Our simulations allow for predicting the dynamics and developing control schemes, which is a basic ingredient for applications in the field of quantum information technology.

Currently we work on:

  • Semiconductor quantum dots for quantum information technology

    Semiconductor quantum dots exhibit a discrete energy spectrum which can be tailored by the quantum dot geometry. The quantum dot states can be well controlled using laser light. Quantum dots can be embedded in microcavities to study solid state quantum optics effects. Because quantum dots can emit single of entangled photons, they are highly attractive to applications in quantum information technology. In contrast to atoms, quantum dots are always subject to the coupling to phonons, which can result in unwanted effects, but also in fascinating, new phenomena.

    On the one hand we study phonon effects on the optical manipulation of quantum dots. On the other hand, we are also interested in the photon states which are generated by quantum dots. Furthermore, we analyze higher excited states in the quantum dot. For the description we use different analytical and numerical methods.

    Current projects:

    • Phonon effects in quantum dots (Miriam Neumann, in collaboration with AG Kuhn of WWU Münster and AG Axt from Bayreuth)
    • Quantum dots for the generation of (entangled) photons (Thomas Bracht, Andreas Völker, in collaboration with AG Axt aus Bayreuth, AG Rastelli from Linz AG Weihs from Innsbruck)
    • Higher excited states in quantum dots (Matthias Holtkemper, Jan Kaspari, in collaboration with AG Kuhn of WWU Münster and AG Leitenstorfer from Konstanz and AG Machnikowski from Wrocław)

  • Carrier dynamics in ultra-thin semiconductors

    Nowadays it is possible to fabricate ultrathin semiconductors consisting only of one or a few monolayers of atoms. Examples are graphene, which has a vanishing band gap, and transition metal dichalcogenides (TMDCs) having a finite band gap. Those materials are effectively two-dimensional. Using deformation one can create a potential dip in these sheets, which acts like a potential well for the charge carriers. Carriers can be captured inside the potential through interaction with, e.g., phonons.

    We study the dynamics of charge carriers traveling inside these new semiconductor materials. To account for the ultrashort time and length scales, a quantum mechanical description is required. We take special care of the locality of the scattering processes and analyse the spatio-temporal dynamics of the carriers considering different interaction mechanisms.

    Current projects (in collaboration with AG Kuhn):

    • Spatiotemporal carrier dynamics in TMDCs (Frank Lengers, Roberto Rosati)
    • Optical detection of spatiotemporal dynamics in semiconductors (Frank Lengers, Andreas Völker)

  • Interaction of nanostructures with complex light fields

    A beam of light is often described by a plane wave, which has spatially homogeneous wavefronts. In contrast, complex light fields have spatially inhomogeneous wavefronts resulting in a complex phase relation. One example is the so called twisted light, which has a helical wave front and a phase singularity implying a zero of intensity at the beam axis. A twisted light beam carries an orbital angular momentum, which could be used in communication technology to encode information. When such a light beam interacts with matter, different processes can be excited compared to the excitation with a plane wave. One of our projects aims at the mathematical formulation of the interaction of twisted light with matter. Other projects deal with the numerical simulation of the interaction of twisted light with metallic nanostructures exhibiting plasmonic resonances.

    Current projects:

    • Interaction of complex light fields with plasmonic nano-antennas (Richard Kerber, in cooperation with Jamie Fitzgerald, from Chalmers, Sang Soon Oh from Cardiff University, UK, and Ortwin Hess from Imperial College London, UK)

    • Theoretical formulation of the interaction of twisted light with matter (in cooperation with Guillermo Quinteiro from Corrientes, Argentina)

  • Controlling light using nanostructures

    Using nanostructured materials the properties of light can be controlled and manipulated. One example are photonic crystals, where a periodic structure of the material leads to a photonic band gap, in which light cannot propagate through the system. By putting a defect in a photonic crystal, a localized mode can be confined in the defect area, i.e., a cavity is formed. One important question is how the localized mode inside the cavity can be excited by a quantum emitter.

    A second example is the control of light using metallic nanostructures showing plasmonic resonances. Using, e.g., a pair of plasmonic nanostructures, light can be extremely enhanced in-between them. This results in a strong light-matter coupling between the field and a quantum system which is placed in the field maximum.

    To study these fascinating nanostructures, we mostly perform numerical simulations, often using already existing software packages. Our focus is to understand the light-matter interaction at the nanoscale.

    Current projects:

    • Coupling of single emitters into photonic crystal cavities (Jan Olthaus, in collaboration with the AG Schuck of the WWU Münster)
    • Light enhancement by plasmonic nanostructures

  •  Projekte

    • laufende Projekte (als Antragstellerin)

      • Simulation der optisch induzierten und räumlich aufgelösten Ladungsträgerdynamik in zweidimensionalen Halbleiter
        DFG, Förderung seit 2018