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


    Current projects (together with Reiter group)

    • Phonon-effects at the excitation of a single quantum dot with chirped laser pulses (Sebastian Lüker)
    • Pump-probe spectroscopy on single quantum dots (Matthias Holtkemper)
    • Four-wave mixing spectroscopy on single nanostructures (Daniel Wigger)
    • Phonon-assisted capturing processes into localized states (Roberto Rosati)

    Finished theses

    Dissertations

    • D. Wigger, Interplay between acoustig phonons and excitons in optically driven semiconductor quantum dots (2017)
    • J. Daniels, Excitonic States and Optical Transitions in Undoped and Mn-Doped Double Quantum Dots (2014)
    • J. Huneke, Modeling Ultrafast Few Carrier Dynamics in Quantum Dots: Coulomb Correlations and Carrier Relaxation Processes (2011)

    Master and Diploma theses

    • M. Holtkemper, Exzitonische und biexzitonische Zustände in Mn-dotierten Quantenpunkten (2013)
    • D. Thuberg, Optical Switching in a III-V Semiconductor Quantum Dot doped with a Single Mn (2012)
    • E. Kahlhöfer, Einfluss der Valenzbandmischung auf die Spindynamik in Mangan-dotierten Quantenpunkten (2012)
    • S. Lüker, Einfluss akustischer Phononen auf die optische Kontrolle von Halbleiter-Quantenpunkten (2012)

    Bachelor theses

    • M. Wolff, Einfluss der Rotating-Wave-Approximation auf die laserpulsinduzierte Besetzungsdynamik in einem Zwei-Niveau-System (2015)
    • F. Stegemerten, Simulation der 2D-Vier-Wellen-Misch-Spektroskopie für Zwei- und Drei-Niveau-Systeme (2015)
    • J. Michel, Anregung von Mehr-Niveau-Quantenpunktsystemen mit frequenzmodulierten Lichtpulsen (2015)
    • D. Kavajin, Dynamik von Wenig-Niveau-Systemen angeregt durch frequenzmodulierte Laserpulsen (2014)

    Selected publications

    • Coherent and robust high-fidelity generation of a biexciton in a quantum dot by rapid adiabatic passage
      T. Kaldewey, S. Lüker, A.V. Kuhlmann, S.R. Valentin, A. Ludwig, A.D. Wieck, D.E. Reiter, T. Kuhn, and R.J. Warburton
      Phys. Rev. B 95, 161302(R) (2017)
    • Lindblad approach to spatiotemporal quantum dynamics of phonon-induced carrier capture processes
      R. Rosati, D.E. Reiter, and T. Kuhn
      Phys. Rev. B 95, 165302 (2017)
    • Impact of Phonons on Dephasing of Individual Excitons in Deterministic Quantum Dot Microlenses
      T. Jakubczyk, V. Delmonte, S. Fischbach, D. Wigger, D.E. Reiter, Q. Mermillod, P. Schnauber, A. Kaganskiy, J.-H. Schulze, A. Strittmatter, S. Rodt, W. Langbein, T. Kuhn, S. Reitzenstein, and J. Kasprzak
      ACS Photonics, 3, 2461  (2016)
    • Fast and selective phonon-assisted state preparation of a quantum dot by adiabatic undressing
      A.M. Barth, S. Lüker, A. Vagov, D.E. Reiter, T. Kuhn, and V.M. Axt
      Phys. Rev. B 94, 045306 (2016)
    • Nanoscale Positioning of Single-Photon Emitters in Atomically Thin WSe2
      J. Kern, I. Niehues, P. Tonndorf, R. Schmidt, D. Wigger, R. Schneider, T. Stiehm, S. Michaelis de Vasconcellos, D.E. Reiter, T. Kuhn, and R. Bratschitsch
      Adv. Mater. 28, 7101-7105 (2016)
    • Dynamics of excitons in individual InAs quantum dots revealed in four-wave mixing spectroscopy
      Q. Mermillod, D. Wigger, V. Delmonte, D.E. Reiter, C. Schneider, M. Kamp, S. Höfling, W. Langbein, T. Kuhn, G. Nogues, and J. Kasprzak
      Optica, Vol. 3, No. 4, pp. 377-384 (2016)
    • Coulomb Mediated Hybridization of Excitons in Coupled Quantum Dots
      P.-L. Ardelt, K. Gawarecki, K. Müller, A.M. Waeber, A. Bechtold, K. Oberhofer, J.M. Daniels, F. Klotz, M. Bichler, T. Kuhn, H.J. Krenner, P. Machnikowski, and J.J. Finley
      Phys. Rev. Lett. 116, 077401 (2016)
    • Direct optical state preparation of the dark exciton in a quantum dot
      S. Lüker, T. Kuhn, and D.E. Reiter
      Phys. Rev. B 92, 201305(R) (2015)
    • The role of phonons for exciton and biexciton generation in an optically driven quantum dot
      D.E. Reiter, T. Kuhn, M. Glässl, and V.M. Axt
      J. Phys.: Condens. Matter 26 (2014) 423203
    • Switching between ground states of an InAs quantum dot doped with a single Mn atom
      D. Thuberg, D.E. Reiter, V.M. Axt, and T. Kuhn
      Phys. Rev. B 88, 085312 (2013)
    • Biexciton state preparation in a quantum dot via adiabatic rapid passage: Comparison between two control protocols and impact of phonon-induced dephasing
      M. Glässl, A.M. Barth, K. Gawarecki, P. Machnikowski, M.D. Croitoru, S. Lüker, D.E. Reiter, T. Kuhn and V.M. Axt
      Phys. Rev. B 87, 085303 (2013)
    • Influence of acoustic phonons on the optical control of quantum dots driven by adiabatic rapid passage
      S. Lüker, K. Gawarecki, D.E. Reiter, A. Grodecka-Grad, V.M. Axt, P. Machnikowski, and T. Kuhn
      Phys. Rev. B 85, 121302(R) (2012)

  • 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.