Research topics - Prof. Dr. Tilmann Kuhn

The research of the AG Kuhn is focused on the theoretical description and simulation of non-equilibrium dynamics of interacting many-body systems, as it appears in many solid state systems, nanostructures or other systems like ultra cold quantum gases. Current projects are in the fields of:

  • Carrier dynamics in localized semiconductor structures

    Quantum dots (QDs) are semiconductor nanostructures in which the movement of electrons is confined to the nanometer scale. This leads to a discrete energy spectrum just like in atoms. In contrast to atoms this spectrum is controllable over a wide range, e.g., by choosing material compounds, size and geometry. This property makes QDs attractive candidates for numerous applications in areas ranging from optoelectronics and photonics to quantum information processing.

    By a controlled laser excitation it is possible to selectively influence the carrier states in a semiconductor structure, e.g., in a QD. A real QD is never an isolated system, but it is typically embedded in a solid. Therefore the environment influences the carrier state quite strong. The interactions with the lattice vibrations, which are called phonons in their quantized description, has the most significant effect.

    Schematic picture of an exciton creation with a frequency-modulated laser pulse

    We study how the perturbation of the phonons on the QD can be minimized to optimize the optically induced carrier dynamics in a desired way. For this purpose it is possible to use laser pulses with special properties, e.g., ultrashort or frequency-modulated pulses.

    A detailed knowledge of the carrier dynamics inside the QD plays a crucial role for the desired control of the states. To study the dynamics, nonlinear techniques like pump-probe and four-wave mixing spectroscopy, are suitable tools. We investigate the influence of different interaction mechanisms on the dynamics of the nonlinear spectra, e.g., Coulomb and exchange interaction and the interaction with lattice vibrations.

    Schematic setup of pump-probe and four-wave mixing spectroscopy

    Another central aspect is the capturing of carriers into a QD. Carriers can be created optically or electrically in the surrounding of a QD. The QD then acts as a potential well and works as a trap for the carriers. In the theoretical description of this process the scattering with phonons again plays an important role because they absorb the energy that is set free during the capturing process.

    Capturing process of an electron wave packet into a QD


    finished theses

    Dissertation

    • M. Holtkemper (2020)
      Excited excitonic complexes in quantum dots: Optical properties and light-induced dynamics

    Master thesis

    • T. Hahn (2019)
      Simulation von Vier-Wellen-Misch-Spektroskopie an einem Quantenpunkt im optomechanischen Resonator und an einem zweidimensionalen Halbleiter

    Bachelor thesis

    • J. Jasper (2020)
      Dynamik der Rabioszillationen eines optisch getriebenen Zwei-Niveau-Systems mit Lokaler-Feld-Wechselwirkung
    • F. Stüber (2019)
      Untersuchung der Erzeugung höherer Harmonischer in optisch getriebenen Zweiniveau-Systemen

    selected publications

    • Local field effects in ultrafast light-matter interaction measured by pump-probe spectroscopy of monolayer MoSe2
      A. Rodek, T. Hahn, J. Kasprzak, T. Kasimierczuk, K. Nogajewski, K.E. Połczyńska, K. Watanabe, T. Taniguchi, T. Kuhn, P. Machnikowski, M. Potemski, D. Wigger, and P. Kossacki
      Nanophotonics 10, 2717-2728 (2021)
    • Influence of local fields on the dynamics of four-wave mixing signals from 2D semiconductor systems
      T. Hahn, J. Kasprzak, P. Machnikowski, T. Kuhn, and D. Wigger
      New J. Phys. 23 (2021) 023036
    • Femtosecond Transfer and Manipulation of Persistent Hot-Trion Coherence in a Single CdSe/ZnSe Quantum Dot
      P. Henzler, C. Traum, M. Holtkemper, D. Nabben, M. Erbe, D.E. Reiter, T. Kuhn, S. Mahapatra, K. Brunner, D. V. Seletskiy, and A. Leitenstorfer
      Phys. Rev. Lett. 126, 067402 (2021)
    • Dark exciton preparation in a quantum dot by a longitudinal light field tuned to higher exciton states
      M. Holtkemper, G.F. Quinteiro, D.E. Reiter, and T. Kuhn
      Phys. Rev. Research 3, 013024 (2021)
    • Selection rules for the excitation of quantum dots by spatially structured light beams: Application to the reconstruction of higher excited exciton wave functions
      M. Holtkemper, G.F. Quinteiro, D.E. Reiter, and T. Kuhn
      Phys. Rev. B 102, 165315 (2020)
    • Semiclassical modeling of coupled quantum-dot-cavity systems: From polaritonlike dynamics to Rabi oscillations
      K. Jürgens, F. Lengers, T. Kuhn, and D.E. Reiter
      Phys. Rev. B 101, 235311 (2020)
    • Four-wave mixing dynamics of a strongly coupled quantum-dot-microcavity system driven by up to 20 photons
      D. Groll, D. Wigger, K. Jürgens, T. Hahn, C. Schneider, M. Kamp, S. Höfling, J. Kasprzak, and T. Kuhn
      Phys. Rev. B 101, 245301 (2020)
    • Theory of the absorption line shape in monolayers of transition metal dichalcogenides
      F. Lengers, T. Kuhn, D.E. Reiter
      Phys. Rev. B 101, 155304 (2020)
    • Effective detection of spatio-temporal carrier dynamics by carrier capture
      R. Rosati, F. Lengers, D.E. Reiter, and T. Kuhn
      J. Phys.: Condens. Matter 31 (2019) 28LT01
    • Spatiotemporal dynamics of Coulomb-correlated carriers in semiconductors
      F. Lengers, R. Rosati, T. Kuhn, and D.E. Reiter
      Phys. Rev. B 99, 155306 (2019)
    • Spatial control of carrier capture in two-dimensional materials: Beyond energy selection rules
      R. Rosati, F. Lengers, D.E. Reiter, and T. Kuhn
      Phys. Rev. B 98, 195411 (2018)
    • Rabi oscillations of a quantum dot exciton coupled to acoustic phonons: coherence and population readout
      D. Wigger, C. Schneider, S. Gerhardt, M. Kamp, S. Höfling, T. Kuhn, and J. Kasprzak
      Optica 5 (11), 1442-1450 (2018)
    • Coulomb effects on the photoexcited quantum dynamics of electrons in a plasmonic nanosphere
      A. Crai, A. Pusch, D.E. Reiter, L. Román Castellanos, T. Kuhn, and O. Hess
      Phys. Rev. B 98, 165411 (2018)
    • Comparison of different concurrences characterizing phonon pairs generated in the biexciton cascade in quantum dots coupled to microcavities
      M. Cygorek, F. Ungar, T. Seidelmann, A.M. Barth, A. Vagov, V.M. Axt, and T. Kuhn
      Phys. Rev. B 98, 045303 (2018)
    • Influence of the quantum dot geometry on p-shell transitions in differently charged quantum dots
      M. Holtkemper, D.E. Reiter, and T. Kuhn
      Phys. Rev. B 97, 075308 (2018)
    • Charge and spin control of ultrafast electron and hole dynamics in single CdSe/ZnSe quantum dots
      C. Hinz, P. Gumbsheimer, C. Traum, M. Holtkemper, B. Bauer, J. Haase, S. Mahapatra, A. Frey, K. Brunner, D.E. Reiter, T. Kuhn, D.V. Seletskij, and A. Leitenstorfer
      Phys. Rev. B 97, 045302 (2018)
    • Exploring coherence of individual excitons in InAs quantum dots embedded in natural photonic defects: Influence of the excitation intensity
      D. Wigger, Q. Mermillod, T. Jakubczyk, F. Fras, S. Le-Denmat, D.E. Reiter. S. Höfling, M. Kamp. G. Nogues, C. Schneider, T. Kuhn, and J. Kasprzak
      Phys. Rev. B 96, 165311 (2017)

  • Phonon dynamics and exciton-phonon coupling in nanostructures

    When the charge density in a solid changes this has an influence on the movement of the lattice atoms. Thus it is possible to generate or destroy phonons (quantized vibrations of the lattice atoms) by optical excitations of the electrons in a semiconductor. When a quantum dot (QD) is driven by ultrashort laser pulses the ultrafast change of the carrier density can lead to the creation of wave packets, which spread from the QD as a shock wave. Such wave packets could be used to communicate between different QDs. Additionally the lattice in the surrounding of the QD is distorted by the change in the charge density; this local distortion accompanying the excitation is called a polaron. By a selective manipulation of the excitation it is possible to control the generation and destruction of the phonons.