Institut für Theoretische Physik (ITP)
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Item-typ:Veröffentlichung, Generation of multipartite entanglement in coupled-cavity arrays as a resource for quantum technologies(2023-10-11); ; ; Entanglement is an essential part of quantum mechanics and a resource for most quantum technologies. While entangled two-particle Bell states are well established, the generation and classification of entanglement in multipartite systems is much more difficult to achieve. At the same time, multipartite entanglement is the key to unlock the full advantage provided by the exponentially large Hilbert space of quantum systems. This thesis explores possibilities of entanglement generation with a specific focus on applications in quantum technologies. In systems of coupled microcavity arrays, coherent optical pulses are considered to directly drive the quantum system into multipartite entangled target states. The building block of such coupled-cavity arrays consists of a single mode cavity with a two-level emitter, whose interaction is described by the Jaynes–Cummings model. In order to gain insight into the system, a novel representation of its eigenspectrum is presented, which shows the eigenenergies and the composition of the corresponding eigenstates. Based on this, a numerical scheme, which is the central achievement of this thesis, is developed that allows to determine precise excitation parameters to generate entanglement. Finally, this scheme is used to show the generation of multipartite entanglement in the form of W and phased Dicke states with high fidelity.Dissertation342 220 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Einstein in der Schule – Teil 1 – Unterrichtskonzepte zur allgemeinen RelativitätstheorieDie allgemeine Relativitätstheorie, ART, ist grundlegend für das Denken in Raum und Zeit und daher für viele Schüler*innen interessant. Hier zeige ich, wie Lernende ein Astrofoto aufnehmen, daran die relativistische Lichtablenkung messen und, ausgehend von ihren Basiskonzepten, wesentliche Konzepte der ART entwickeln. Dazu berichte ich über Erfahrungen in den Klassenstufen 5-12. Auch präsentiere ich Material, das für den Unterricht in Astronomie, Physik und Mathematik geeignet ist.Wissenschaftlicher ArtikelBand:55Heft:3-4153 104 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Einstein in der Schule – Teil 2 – Unterrichtskonzepte zur allgemeinen RelativitätstheorieDie allgemeine Relativitätstheorie, ART, ist grundlegend für das Denken in Raum und Zeit und daher für viele Schüler*innen interessant. Hier zeige ich, wie Lernende ein Astrofoto aufnehmen, daran die relativistische Lichtablenkung messen und, ausgehend von ihren Basiskonzepten, wesentliche Konzepte der ART entwickeln. Dazu berichte ich über Erfahrungen in den Klassenstufen 5-12. Auch präsentiere ich Material, das für den Unterricht in Astronomie, Physik und Mathematik geeignet ist.Wissenschaftlicher ArtikelBand:55Heft:6107 72 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Theoretical modelling of semiconductor nanolasers: On the influence of many-body effects on the optical properties of semiconductor nanostructures(2025-12-10); ; ; The rapid rise in global data centre energy consumption poses a critical challenge in the age of digitalisation and artificial intelligence. A promising strategy for improving energy efficiency involves the use of on-chip integrated photonic components to enable high-speed and low-loss optical links and photonic computing platforms. Realising this vision requires integrable laser sources on the nanoscale. This dissertation develops a comprehensive theoretical framework for semiconductor nanolasers, with a particular emphasis on the influence of quantum many-body effects on the optical properties of low-dimensional gain media. This work is structured to consist of three interdependent chapters. The first chapter investigates a metallic-cavity nanolaser incorporating multiple quantum wells. A fully quantised electromagnetic field formalism is employed and Quantum Laser Equations are derived on the quadruplet-level. These equations enable access to key observables including the input-output characteristics, coherence time, and second-order correlation function at zero delay. Theoretical predictions are shown to be in substantial agreement with experimental data from a silver-coated MQW nanolaser device. A spectral lineshape anomaly is identified: A transition from a Lorentzian to a Gaussian emission profile at the lasing threshold, attributed to intrinsic non-linear effects and partial mode-locking in the open cavity system. The second chapter establishes a microscopic model of monolayer molybdenum disulfide, a transition metal dichalcogenide, as a gain material. Based on a tight-binding approach, material-specific dipole and Coulomb matrix elements are derived and energy renormalisations via the screened-exchange Coulomb-hole approximation are introduced to account for the influence of screening due to the presence of excited carriers. Absorption spectra are generated using the Semiconductor Bloch Equations, demonstrating the importance of screening effects in shaping the optical response. The impact of the Brillouin zone sampling density on computational efficiency and spectral accuracy is systematically analysed and a minimum carrier density for the expectation of gain is quantified. The third and final chapter combines insights gained in the previous two and proposes a theoretical nanolaser device consisting of a molybdenum disulfide monolayer integrated with a photonic crystal cavity. A material-oriented doublet-level formulation of the Quantum Laser Equations is developed to manage the multiscale dynamics, spanning femtosecond Coulomb processes to nanosecond lasing behaviour. The theory predicts electron-hole-plasma-based lasing at room temperature, characterised by an S-shaped input-output curve, hole burning at the K- and K′-valley, and spectral clamping. These features are indicative of lasing driven by plasma gain at high carrier densities and emerge naturally from the material-oriented quantum-optical treatment of the device. Together, the three chapters establish a consistent, predictive, and microscopically realistic theoretical framework for semiconductor nanolasers. The developed models combine quantum-optical treatments with device-level properties focused on the utilised gain media, enabling a detailed understanding of the interplay between many-body physics and stimulated emission in nanoscale systems. These results contribute to the design of next-generation nanophotonic light sources and offer a pathway towards energy-efficient, on-chip integrated lasers suitable for future optical links and photonic computing platforms.Dissertation48 64 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Many-body effects and quantum-optical mode coupling in semiconductor lasers(2025-09-29); ; 34 52 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Emission properties of high-β nanolasers with continuous gain media(2020-06-25); ; ; The search for ever smaller and more efficient sources of coherent light motivated the development of lasers with dimensions on the nanoscale. These consist of dielectric or metallic cavity structures that confine light close or even below the diffraction limit and can be integrated into on-chip photonics which makes them interesting candidates for applications in quantum information and communication and integrated photonic circuits. While semiconductor quantum dots were much investigated as gain media for such lasers, recently also extended, two- dimensional gain media are considered. Semiconductor quantum wells are already employed in micro laser (e.g. VCSELs) on an industrial scale, and, improved fabrication techniques, have now been pushed to the nanoscale as well. Furthermore, new classes of atomically thin 2d layers of transition metal dichalcogenide (TMD) have emerged as an exciting candidate for optical applications due to their strong optical activity. In this thesis we contribute to the field by developing and employing quantum-optical semiconductor laser models that give direct access to conventional laser characteristics as well as photon-correlation functions. Using equation of motion techniques and the cluster-expansion approximation we find that nanolasers with extended gain media operating close to the thresholdless regime have a distinctly different threshold behavior in comparison to quantum-dot-based nanolasers. These findings shed new light on the behavior of nanolaser in their transition from thermal to coherent emission. Furthermore we provide gain calculations for single layers of different TMD materials, that take into account many-body interaction leading to band structure renormalizations and dephasing processes. Together with a rate-equation theory that is adapted to account for the particular device geometry, we highlight prospects and limitations of TMD materials for applications in nanolasers. Finally we develop a quantum-optical semiconductor laser theory that we apply to the description of realistic quantum-well-based nanolasers. Together with experimental partners we unambiguously show the onset of lasing emission from different device types and create a comprehensive picture of the internal processes that define the dynamics of these devices.Dissertation381 418