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. 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

    PhD theses

    • D. Groll (2023)
      Theory of solid state single photon emitters: From incoherent to coherent spectroscopy
    • M. Holtkemper (2020)
      Excited excitonic complexes in quantum dots: Optical properties and light-induced dynamics

    Master theses

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

    Bachelor theses

    • Gregor Beyer (2023)
      Optische Eigenschaften und Zustandspräparation eines optisch getriebenen Drei-Niveau-Systems mit phonondinduzierten Übergängen

    • 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

    • Resonant and phonon-assisted ultrafast coherent control of a single hBN color center
      J.A. Preuss, D. Groll, R. Schmidt, T. Hahn, P. Machnikowski, R. Bratschitsch, T. Kuhn, S. Michaelis de Vasconcellos, and D. Wigger
      Optica 9 (5), 522-531 (2022)
    • Single-Photon Emitters in Layered Van der Waals Materials
      S. Michaelis de Vasconcellos, D. Wigger, U. Wurstbauer, A.W. Holleitner, R. Bratschitsch, T. Kuhn
      Phys. Status Solidi B 259, 2100566 (2022)
    • Destructive Photon Echo Formation in Six-Wave Mixing Signals of MoSe2 Monolayer
      T. Hahn, D. Vaclavkova, M. Bartos, K. Nogajewski, M. Potemski, K. Watanabe, T. Taniguchi, P. Machnikowski, T. Kuhn, J. Kasprzak, and D. Wigger
      Adv. Sci. 9, 2103813, 2022
    • Comparison of the semiclassical and quantum optical field dynamics in a pulse-excited optical cavity with a finite number of quantum emitters
      K. Jürgens, F. Lengers, D. Groll, D.E. Reiter, D. Wigger, and T. Kuhn
      Phys. Rev. B 104, 205308 (2021)
    • 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.

    Phonon wave packet after ultrafast excitation in a quantum dot (QD)

     

    Furthermore the coupling between the charge dynamics and the dynamics of the phonons provides the possibility to selectively create phonon states with interesting quantum mechanical properties, by optical manipulation of the electronic system. By applying tricky excitations it is possible to create so called Schrödinger-cat states, i.e., states, which consist of a superposition of quasi-classical coherent states. In such states the quantum mechanical uncertainty of a variable can by significantly reduced under suitable conditions; such states are called squeezed states, in analogy to those well known from quantum optics.

    Wigner function of two Schrödinger-cat states

     

    Acoustic waves can already be used to control the intensity of quantum dot lasers on the time scale of a few picoseconds. In the experiments the wave packets are created through short laser pulses that heat a thin aluminum film. The accompanying thermal expansion of the film launches the sound pulse. When the phonons then reach the QD layer they lead to a change of the transition energies of the QDs. Because the efficiency of the laser depends crucially on the detuning between the QD transitions and the resonator mode the acoustic waves directly influence the intensity of the laser light.

    Schematic picture of the phonon controlled QD laser

     

    finished theses

    PhD theses

    • T. Hahn (2023)
      heory of optically induced dynamics and nonlinear spectroscopy of a quantum dot in an optomechanical resonator and of an atomically thin semiconductor
    • S. Lüker (2018)
      Optical Preparation of Excitonic and Phononic Quantum States in Semiconductor Quantum Dots

    Master theses

    • D. Groll (2018)
      Investigation of the dissipative Jaynes-Cummings model coupled to phonons

    Bachelor theses

    • Anton Plonka (2023)
      Optische Antwort und Phononzustandsdynamik von optomechanischen Systemen nach ultrakurzer optischer Anregung

    • R. Kapust (2021)
      Simulation der Phonondynamik in ein- und zweidimensionalen Heterostrukturen mit dem Masse-Feder-Modell
    • J.A. Ballmeier (2020)
      Akustische Wellen in Kristallstrukturen
    • M. Kampshoff (2020)
      Simulation der Phononpropagation in eindimensionalen Gittern

    selected publications

    • How to Read Out the Phonon Number Statistics via Resonance Fluorescence Spectroscopy of a Single-Photon Emitter
      D. Groll, F. Paschen, P. Machnikowski, O. Hess, D. Wigger, and T. Kuhn
      Adv. Quantum Technol. 2300153 (2023)
    • Photon scattering from a quantum acoustically modulated two-level system
      T. Hahn, D. Groll, H.J. Krenner, T. Kuhn, P. Machnikowski, and D. Wigger
      AVS Quantum Sci. 4, 011403 (2022)
    • Resonance-fluorescence spectral dynamics of an acoustically modulated quantum dot
      D. Wigger, M. Weiß, M. Lienhart, K. Müller, J.J. Finley, T. Kuhn, H.J. Krenner, and P. Machnikowski
      Phys. Rev. Research 3, 033197 (2021)
    • Optomechanical wave mixing by a single quantum dot
      M. Weiß, D. Wigger, M. Nägele, K. Müller, J.J. Finley, T. Kuhn, P. Machnikowski, and H.J. Krenner
      Optica 8, pp. 291-300 (2021)
    • Controlling Photoluminescence Spectra of hBN Color Centers by Selective Phonon-Assisted Excitation: A Theoretical Proposal
      D. Groll, T. Hahn, P. Machnikowski, D. Wigger, and T. Kuhn
      Mater. Quantum. Technol. 1 (2021) 015004
    • Entropy Dynamics of Phonon Quantum States Generated by Optical Excitation of a Two-Level System
      T. Hahn, D. Wigger and T. Kuhn
      Entropy 2020, 22 (3), 286
    • Acoustic phonon sideband dynamics during polaron formation in a single quantum dot
      D. Wigger, V. Karakhanyan, C. Schneider, M. Kamp, S. Höfling, P. Machnikowski, T. Kuhn, and J. Kasprzak
      Optics Letters 45, 919-922 (2020)
    • Phonon-Induced Enhancement of Photon Entanglement in Quantum Dot-Cavity Systems
      T. Seidelmann, F. Ungar, A.M. Barth, A. Vagov, V.M. Axt, M. Cygorek, and T. Kuhn
      Phys. Rev. Lett. 123, 137401 (2019)
    • Distinctive characteristics of carrier-phonon interactions in optically driven semiconductor quantum dots
      D.E. Reiter, T. Kuhn and V.M. Axt
      Adv. Phys-X 4, 1655478 (2019)
    • Influence of excited state decay and dephasing on phonon quantum state preparation
      T. Hahn, D. Groll, T. Kuhn, and D. Wigger
      Phys. Rev. B 100, 024306 (2019)
    • From strong to weak temperature dependence of the two-phonon entanglement resulting from the biexciton cascade inside a cavity
      T. Seidelmann, F. Ungar, M. Cygorek, A. Vagov, A.M. Barth, T. Kuhn, and V.M. Axt
      Phys. Rev. B 99, 245301 (2019)
    • Phonon-assisted emission and absorption of individual color centers in hexagonal boron nitride
      D. Wigger, R. Schmidt, O. Del Pozo-Zamudio, J.A. Preuß, P. Tonndorf, R. Schneider, P. Steeger, J. Kern, Y. Khodaei, J. Sperling, S. Michaelis de Vasconcellos, R. Bratschitsch, and T. Kuhn
      2D Mater. 6, 035006 (2019)
    • Coherent phonon lasing in a thermal quantum nanomachine
      P. Karwat, D.E. Reiter, T. Kuhn, and O. Hess
      Phys. Rev. A 98, 053855 (2018)
    • Strain Control of Exciton-Phonon Coupling in Atomically Thin Semiconductors
      I. Niehues, R. Schmidt, M. Drüppel, P. Marauhn, D. Christiansen, M. Selig, G. Berghäuser, D. Wigger, R. Schneider, L. Braasch, R. Koch, A. Castellanos-Gomez, T. Kuhn, A. Knorr, E. Malic, M. Rohlfing, S. Michaelis de Vasconcellos, and R. Bratschitsch
      Nano Lett., 2018, 18 (3), pp. 1751-1757
    • Phonon impact on optical control schemes of quantum dots: Role of quantum dot geometry and symmetry
      S. Lüker, T. Kuhn, and D.E. Reiter
      Phys. Rev. B 96, 245306 (2017)
    • Systematic study of the influence of coherent phonon wave packets on the lasing properties of a quantum dot ensemble
      D. Wigger, T. Czerniuk, D.E. Reiter, M. Bayer, and T. Kuhn
      New J. Phys. 19 (2017) 073001
    • Phonon-assisted dark exciton preparation in a quantum dot
      S. Lüker, T. Kuhn, and D.E. Reiter
      Phys. Rev. B 95, 195305 (2017)