@inproceedings{50287, author = {{Kruse, Stephan and Schwabe, Tobias and Kneuper, Pascal and Kurz, Heiko G. and Meinecke, March-Michael and Scheytt, Christoph}}, booktitle = {{German Microwave Conference (GeMiC) }}, title = {{{Analysis and Simulation of a Photonic Multiband FMCW Radar Sensor System using Nyquist Pulses}}}, doi = {{10.23919/GeMiC59120.2024.10485320}}, year = {{2024}}, } @inproceedings{54785, author = {{Kruse, Stephan and Schwabe, Tobias and Kneuper, Pascal and Scheytt, J. Christoph}}, booktitle = {{INTERNATIONAL CONFERENCE RADAR 2024}}, location = {{RENNES}}, title = {{{A Photonic Multiband Radar Transmitter Architecture with Tailored Nonlinear Transmission Line}}}, year = {{2024}}, } @inproceedings{53797, author = {{Kruse, Stephan and Kneuper, Pascal and Schwabe, Tobias and Kurz, Heiko G. and Meinecke, Marc-Michael and Gonzalez-Huici, María A. and Scheytt, J. Christoph}}, booktitle = {{International Conference on Microwaves for Intelligent Mobility (ICMIM)}}, title = {{{Phase Noise Analysis of Photonic Radar Systems with Optical LO Distribution}}}, year = {{2024}}, } @inproceedings{53800, author = {{Kruse, Stephan and Brockmeier, Jan and Kneuper, Pascal and Schwabe, Tobias and Kurz, Heiko G. and Meinecke, Marc Michael and Scheytt, J. Christoph}}, booktitle = {{ International Radar Symposium (IRS)}}, title = {{{Doppler Analysis of a Lidar-Photonic Radar Combined Sensor System}}}, year = {{2024}}, } @article{59269, abstract = {{Ferroelectric materials play a crucial role in a broad range of technologies due to their unique properties that are deeply connected to the pattern and behavior of their ferroelectric (FE) domains. Chief among them, barium titanate (BaTiO3; BTO) sees widespread applications such as in electronics but equally is a ferroelectric model system for fundamental research, e.g., to study the interplay of such FE domains, the domain walls (DWs), and their macroscopic properties, owed to BTO’s multiple and experimentally accessible phase transitions. Here, we employ Second Harmonic Generation Microscopy (SHGM) to in situ investigate the cubic-to-tetragonal (at ∼126°C) and the tetragonal-to-orthorhombic (at ∼5°C) phase transition in single-crystalline BTO via three-dimensional (3D) DW mapping. We demonstrate that SHGM imaging provides the direct visualization of FE domain switching as well as the domain dynamics in 3D, shedding light on the interplay of the domain structure and phase transition. These results allow us to extract the different transition temperatures locally, to unveil the hysteresis behavior, and to determine the type of phase transition at play (first/second order) from the recorded SHGM data. The capabilities of SHGM in uncovering these crucial phenomena can easily be applied to other ferroelectrics to provide new possibilities for in situ engineering of advanced ferroic devices.}}, author = {{Kirbus, Benjamin and Seddon, Samuel D. and Kiseleva, Iuliia and Beyreuther, Elke and Rüsing, Michael and Eng, Lukas M.}}, issn = {{0021-8979}}, journal = {{Journal of Applied Physics}}, number = {{15}}, publisher = {{AIP Publishing}}, title = {{{Probing ferroelectric phase transitions in barium titanate single crystals via in-situ second harmonic generation microscopy}}}, doi = {{10.1063/5.0237769}}, volume = {{136}}, year = {{2024}}, } @article{59271, abstract = {{Lithium niobate (LNO) and lithium tantalate (LTO) see widespread use in fundamental research and commercial technologies reaching from electronics over classical optics to integrated quantum communication. The mixed crystal system lithium niobate tantalate (LNT) allows for the dedicate engineering of material properties by combining the advantages of the two parental materials LNO and LTO. Vibrational spectroscopies such as Raman spectroscopy or (Fourier transform) infrared (IR) spectroscopy are vital techniques to provide detailed insight into the material properties, which is central to the analysis and optimization of devices. This work presents a joint experimental–theoretical approach allowing to unambiguously assign the spectral features in the LNT material family through both Raman and IR spectroscopy, as well as providing an in‐depth explanation for the observed scattering efficiencies based on first‐principles calculations. The phononic contribution to the static dielectric tensor is calculated from the experimental and theoretical data using the generalized Lyddane–Sachs–Teller relation and compared with the results of the first‐principles calculations.}}, author = {{Bernhardt, Felix and Gharat, Soham and Kapp, Alexander and Pfeiffer, Florian and Buschbeck, Robin and Hempel, Franz and Pashkin, Oleksiy and Kehr, Susanne C. and Rüsing, Michael and Sanna, Simone and Eng, Lukas M.}}, issn = {{1862-6300}}, journal = {{physica status solidi (a)}}, number = {{1}}, pages = {{2300968}}, publisher = {{Wiley}}, title = {{{Lattice Dynamics of LiNb(1–x)Ta(x)O3 Solid Solutions: Theory and Experiment}}}, doi = {{10.1002/pssa.202300968}}, volume = {{222}}, year = {{2024}}, } @article{59270, abstract = {{Lithium niobate tantalate (LiNb1−xTaxO3, LNT) solid solutions offer exciting new possibilities for applications ranging from optics, piezotronics, and electronics beyond the capabilities of the widely used singular compounds of lithium niobate (LiNbO3, LN) or lithium tantalate (LiTaO3, LT). Crystal growth of homogeneous LNT single crystals by the Czochralski method is still challenging. One key aspect of homogeneous growth is the accurate knowledge of thermal conductivity through the crystal boule during the growth, which is central to control the crystal growth. Therefore, the temperature dependent thermal conductivity of pure LN, LT, and LNT solid solutions, as well as of selected doped LN and LT crystals (Mg, Zn) was investigated across the temperature range from 300 to 1300 K. The results that span across the whole composition range can directly be applied for optimizing growth conditions of both LNT solid solutions as well as doped and undoped LN and LT crystals.}}, author = {{Bashir, Umar and Rüsing, Michael and Klimm, Detlef and Blukis, Roberts and Koppitz, Boris and Eng, Lukas M. and Bickermann, Matthias and Ganschow, Steffen}}, issn = {{0925-8388}}, journal = {{Journal of Alloys and Compounds}}, publisher = {{Elsevier BV}}, title = {{{Thermal conductivity in solid solutions of lithium niobate tantalate single crystals from 300 K up to 1300 K}}}, doi = {{10.1016/j.jallcom.2024.176549}}, volume = {{1008}}, year = {{2024}}, } @article{59272, abstract = {{Ferroelectrics such as LiNbO3 (LN) are wide-band-gap insulators that may show a high local electric conductivity at the domain walls (DWs). The latter are interfaces separating regions of noncollinear polarization, which can be manipulated to build integrated nanoelectronic elements. In the present work, we model different DW types in LN from first principles. Our models reveal the DW morphology and shed light on their electronic properties: A strong band bending is predicted for charged DWs, leading to local metallicity. Defect trapping at the DW may further enhance the electric conductivity.}}, author = {{Verhoff, Leonard M. and Pionteck, Mike N. and Rüsing, Michael and Fritze, Holger and Eng, Lukas M. and Sanna, Simone}}, issn = {{2643-1564}}, journal = {{Physical Review Research}}, number = {{4}}, publisher = {{American Physical Society (APS)}}, title = {{{Two-dimensional electronic conductivity in insulating ferroelectrics: Peculiar properties of domain walls}}}, doi = {{10.1103/physrevresearch.6.l042015}}, volume = {{6}}, year = {{2024}}, } @article{59273, abstract = {{Ferroelectric domain walls (DWs) are promising structures for assembling future nano-electronic circuit elements on a larger scale since reporting domain wall currents of up to 1 mA per single DW. One key requirement hereto is their reproducible manufacturing by gaining preparative control over domain size and domain wall conductivity (DWC). To date, most works on DWC have focused on exploring the fundamental electrical properties of individual DWs within single-shot experiments, with an emphasis on quantifying the origins of DWC. Very few reports exist when it comes to comparing the DWC properties between two separate DWs, and literally nothing exists where issues of reproducibility in DWC devices have been addressed. To fill this gap while facing the challenge of finding guidelines for achieving predictable DWC performance, we report on a procedure that allows us to reproducibly prepare single hexagonal domains of a predefined diameter into uniaxial ferroelectric lithium niobate single crystals of 200 and 300 μm thickness, respectively. We show that the domain diameter can be controlled with an uncertainty of a few percent. As-grown DWs are then subjected to a standard procedure of current-limited high-voltage DWC enhancement, and they repetitively reach a DWC increase of six orders of magnitude. While all resulting DWs show significantly enhanced DWC values, their individual current–voltage (I–V) characteristics exhibit different shapes, which can be explained by variations in their 3D real structure reflecting local heterogeneities by defects, DW pinning, and surface-near DW inclination.}}, author = {{Ratzenberger, Julius and Kiseleva, Iuliia and Koppitz, Boris and Beyreuther, Elke and Zahn, Manuel and Gössel, Joshua and Hegarty, Peter A. and Amber, Zeeshan H. and Rüsing, Michael and Eng, Lukas M.}}, issn = {{0021-8979}}, journal = {{Journal of Applied Physics}}, number = {{10}}, pages = {{104302}}, publisher = {{AIP Publishing}}, title = {{{Toward the reproducible fabrication of conductive ferroelectric domain walls into lithium niobate bulk single crystals}}}, doi = {{10.1063/5.0219300}}, volume = {{136}}, year = {{2024}}, } @article{59274, abstract = {{Recently, ion exchange (IE) has been used to periodically modify the coercive field (Ec) of the crystal prior to periodic poling, to fabricate fine-pitch domain structures in Rb-doped KTiOPO4 (RKTP). Here, we use micro-Raman spectroscopy to understand the impact of IE on the vibrational modes related to the Rb/K lattice sites, TiO octahedra, and PO4 tetrahedra, which all form the basis of the RKTP crystal structure. We analyze the Raman spectra of three different RKTP samples: (1) a RKTP sample that shows a poled domain grating only, (2) a RKTP sample that has an Ec grating only, and (3) a RKTP sample that has both an Ec and a domain grating of the nominally same spacing. This allows us to determine the impact of IE on the vibrational modes of RKTP. We characterize the changes in the lower Raman peaks related to the alkali-metal ions, as well as observe lattice modifications induced by the incorporation of Rb+ that extend further into the crystal bulk than the expected IE depth. Moreover, the influence of IE on the domain walls is also manifested in their Raman peak shift. We discuss our results in terms of the deformation of the PO4and TiO groups. Our results highlight the intricate impact of IE on the crystal structure and how it facilitates periodic poling, paving the way for further development of the Ec-engineering technique.}}, author = {{Lee, Cherrie S. J. and Canalias, Carlota and Buschbeck, Robin and Koppitz, Boris and Hempel, Franz and Amber, Zeeshan and Eng, Lukas M. and Rüsing, Michael}}, issn = {{2469-9950}}, journal = {{Physical Review B}}, number = {{21}}, publisher = {{American Physical Society (APS)}}, title = {{{Impact of ion exchange on vibrational modes in Rb-doped KTiOPO4: A Raman spectroscopy study on the interplay between ion exchange and polarization switching}}}, doi = {{10.1103/physrevb.110.214115}}, volume = {{110}}, year = {{2024}}, } @article{59275, abstract = {{Studying and understanding many‐body interactions, particularly electron‐boson interactions, is essential for a deeper elucidation of fundamental physical phenomena and the development of novel material functionalities. Here, this aspect is explored in the weak itinerant ferromagnet LaCo2P2 by means of momentum‐resolved photoelectron spectroscopy (ARPES) and first‐principles calculations. The detailed ARPES patterns enable to unveil bulk and surface bands, spin splittings due to Rashba and exchange interactions, as well as the evolution of bands with temperature, which altogether creates a solid foundation for theoretical studies. The latter has allowed to establish the impact of electron‐boson interactions on the electronic structure, that are reflected in its strong renormalization driven by electron‐magnon interaction and the emergence of distinctive kinks of surface and bulk electron bands due to significant electron‐phonon coupling. Our results highlight the distinct impact of electron‐boson interactions on the electronic structure, particularly on the itinerant d states. Similar electronic states are observed in the isostructural iron pnictides, where electron‐boson interactions play a crucial role in the emergence of superconductivity. It is believed that further studies of material systems involving both magnetically active d‐ and f‐sublattices will reveal more advanced phenomena in the bulk and at distinct surfaces, driven by a combination of factors including Rashba and Kondo effects, exchange magnetism, and electron‐boson interactions.}}, author = {{Usachov, D. Yu. and Ali, K. and Poelchen, G. and Mende, M. and Schulz, S. and Peters, M. and Bokai, K. and Sklyadneva, I. Yu. and Stolyarov, V. and Chulkov, E. V. and Kliemt, K. and Paischer, S. and Buczek, P. A. and Heid, R. and Hempel, F. and Rüsing, Michael and Ernst, A. and Krellner, C. and Eremeev, S. V. and Vyalikh, D. V.}}, issn = {{2751-1200}}, journal = {{Advanced Physics Research}}, publisher = {{Wiley}}, title = {{{Unveiling Electron‐Phonon and Electron‐Magnon Interactions in the Weak Itinerant Ferromagnet LaCo2P2}}}, doi = {{10.1002/apxr.202400137}}, year = {{2024}}, } @article{54967, abstract = {{Ferroelectric domain wall conductivity (DWC) is an intriguing and promising functional property that can be elegantly controlled and steered through a variety of external stimuli such as electric and mechanical fields. Optical-field control, as a noninvasive and flexible tool, has rarely been applied so far, but it significantly expands the possibility for both tuning and probing DWC. On the one hand, as known from second-harmonic or Raman micro-spectroscopy, the optical approach provides information on DW distribution and inclination, while simultaneously probing the DW vibrational modes; on the other hand, photons might be applied to directly generate charge carriers, thereby acting as a functional and spectrally tunable probe to deduce the local absorption properties and bandgaps of conductive DWs. Here, we report on investigating the photo-induced DWC (PI-DWC) of three lithium niobate crystals, containing a very different number of DWs, namely: (A) none, (B) one, and (C) many conductive DWs. All three samples are inspected for their current–voltage behavior in darkness and for different illumination wavelengths swept from 500 nm down to 310 nm. All samples show their maximum PI-DWC at 310 nm; moreover, sample (C) reaches PI-DWCs of several microampere. Interestingly, a noticeable PI-DWC is also observed for sub-bandgap illumination, hinting toward the existence and decisive role of electronic in-gap states that contribute to the electronic charge transport along DWs. Finally, complementary conductive atomic force microscopy investigations under illumination proved that the PI-DWC indeed is confined to the DW area and does not originate from photo-induced bulk conductivity.}}, author = {{Ding, L. L. and Beyreuther, E. and Koppitz, B. and Kempf, K. and Ren, J. H. and Chen, W. J. and Rüsing, Michael and Zheng, Y. and Eng, L. M.}}, issn = {{0003-6951}}, journal = {{Applied Physics Letters}}, number = {{25}}, publisher = {{AIP Publishing}}, title = {{{Comparative study of photo-induced electronic transport along ferroelectric domain walls in lithium niobate single crystals}}}, doi = {{10.1063/5.0205877}}, volume = {{124}}, year = {{2024}}, } @article{54966, abstract = {{Piezoresponse force microscopy (PFM) is one of the most widespread methods for investigating and visualizing ferroelectric domain structures down to the nanometer length scale. PFM makes use of the direct coupling of the piezoelectric response to the crystal lattice, and hence, it is most often applied to spatially map the three-dimensional (3D) near-surface domain distribution of any polar or ferroic sample. Nonetheless, since most samples investigated by PFM are at least semiconducting or fully insulating, the electric ac field emerging from the conductive scanning force microscopy (SFM) tip penetrates the sample and, hence, may also couple to polar features that are deeply buried into the bulk of the sample under investigation. Thus, in the work presented here, we experimentally and theoretically explore the contrast and depth resolution capabilities of PFM, by analyzing the dependence of several key parameters. These key parameters include the depth of the buried feature, i.e., here a domain wall (DW), as well as PFM-relevant technical parameters such as the tip radius, the PFM drive voltage and frequency, and the signal-to-noise ratio. The theoretical predictions are experimentally verified using x-cut periodically poled lithium niobate single crystals that are specially prepared into wedge-shaped samples, in order to allow the buried feature, here the DW, to be “positioned” at any depth into the bulk. This inspection essentially contributes to the fundamental understanding in PFM contrast analysis and to the reconstruction of 3D domain structures down to a 1 μm-penetration depth into the sample.}}, author = {{Roeper, Matthias and Seddon, Samuel D. and Amber, Zeeshan H. and Rüsing, Michael and Eng, Lukas M.}}, issn = {{0021-8979}}, journal = {{Journal of Applied Physics}}, keywords = {{Ferroelectrics, lithium niobate, piezoresponse force microscopy}}, number = {{22}}, publisher = {{AIP Publishing}}, title = {{{Depth resolution in piezoresponse force microscopy}}}, doi = {{10.1063/5.0206784}}, volume = {{135}}, year = {{2024}}, } @misc{59259, author = {{Schwabe, Tobias and Rüsing, Michael and Staal, Niels and Schwengelbeck, Max and Bollmers, Laura and Padberg, Laura and Eigner, Christof and Silberhorn, Christine and Scheytt, J. Christoph}}, publisher = {{Zenodo}}, title = {{{Quantum photonic systems in CMOS compatible silicon nitride technology }}}, doi = {{10.5281/zenodo.15124929}}, year = {{2024}}, } @inproceedings{50273, abstract = {{The Polynomial-Time Hierarchy ($\mathsf{PH}$) is a staple of classical complexity theory, with applications spanning randomized computation to circuit lower bounds to ''quantum advantage'' analyses for near-term quantum computers. Quantumly, however, despite the fact that at least \emph{four} definitions of quantum $\mathsf{PH}$ exist, it has been challenging to prove analogues for these of even basic facts from $\mathsf{PH}$. This work studies three quantum-verifier based generalizations of $\mathsf{PH}$, two of which are from [Gharibian, Santha, Sikora, Sundaram, Yirka, 2022] and use classical strings ($\mathsf{QCPH}$) and quantum mixed states ($\mathsf{QPH}$) as proofs, and one of which is new to this work, utilizing quantum pure states ($\mathsf{pureQPH}$) as proofs. We first resolve several open problems from [GSSSY22], including a collapse theorem and a Karp-Lipton theorem for $\mathsf{QCPH}$. Then, for our new class $\mathsf{pureQPH}$, we show one-sided error reduction for $\mathsf{pureQPH}$, as well as the first bounds relating these quantum variants of $\mathsf{PH}$, namely $\mathsf{QCPH}\subseteq \mathsf{pureQPH} \subseteq \mathsf{EXP}^{\mathsf{PP}}$.}}, author = {{Agarwal, Avantika and Gharibian, Sevag and Koppula, Venkata and Rudolph, Dorian}}, booktitle = {{Proceedings of 49th International Symposium on Mathematical Foundations of Computer Science (MFCS)}}, number = {{7}}, pages = {{7--17}}, title = {{{Quantum Polynomial Hierarchies: Karp-Lipton, error reduction, and lower bounds}}}, doi = {{10.4230/LIPIcs.MFCS.2024.7}}, volume = {{306}}, year = {{2024}}, } @inproceedings{50406, abstract = {{What is the power of polynomial-time quantum computation with access to an NP oracle? In this work, we focus on two fundamental tasks from the study of Boolean satisfiability (SAT) problems: search-to-decision reductions, and approximate counting. We first show that, in strong contrast to the classical setting where a poly-time Turing machine requires $\Theta(n)$ queries to an NP oracle to compute a witness to a given SAT formula, quantumly $\Theta(\log n)$ queries suffice. We then show this is tight in the black-box model - any quantum algorithm with "NP-like" query access to a formula requires $\Omega(\log n)$ queries to extract a solution with constant probability. Moving to approximate counting of SAT solutions, by exploiting a quantum link between search-to-decision reductions and approximate counting, we show that existing classical approximate counting algorithms are likely optimal. First, we give a lower bound in the "NP-like" black-box query setting: Approximate counting requires $\Omega(\log n)$ queries, even on a quantum computer. We then give a "white-box" lower bound (i.e. where the input formula is not hidden in the oracle) - if there exists a randomized poly-time classical or quantum algorithm for approximate counting making $o(log n)$ NP queries, then $\text{BPP}^{\text{NP}[o(n)]}$ contains a $\text{P}^{\text{NP}}$-complete problem if the algorithm is classical and $\text{FBQP}^{\text{NP}[o(n)]}$ contains an $\text{FP}^{\text{NP}}$-complete problem if the algorithm is quantum.}}, author = {{Gharibian, Sevag and Kamminga, Jonas}}, booktitle = {{Proceedings of 51st EATCS International Colloquium on Automata, Languages and Programming (ICALP)}}, number = {{70}}, pages = {{1--19}}, title = {{{BQP, meet NP: Search-to-decision reductions and approximate counting}}}, volume = {{297}}, year = {{2024}}, } @unpublished{56944, abstract = {{Quantum Max Cut (QMC), also known as the quantum anti-ferromagnetic Heisenberg model, is a QMA-complete problem relevant to quantum many-body physics and computer science. Semidefinite programming relaxations have been fruitful in designing theoretical approximation algorithms for QMC, but are computationally expensive for systems beyond tens of qubits. We give a second order cone relaxation for QMC, which optimizes over the set of mutually consistent three-qubit reduced density matrices. In combination with Pauli level-$1$ of the quantum Lasserre hierarchy, the relaxation achieves an approximation ratio of $0.526$ to the ground state energy. Our relaxation is solvable on systems with hundreds of qubits and paves the way to computationally efficient lower and upper bounds on the ground state energy of large-scale quantum spin systems.}}, author = {{Huber, Felix and Thompson, Kevin and Parekh, Ojas and Gharibian, Sevag}}, booktitle = {{arXiv:2411.04120}}, title = {{{Second order cone relaxations for quantum Max Cut}}}, year = {{2024}}, } @article{48544, abstract = {{When it comes to NP, its natural definition, its wide applicability across scientific disciplines, and its timeless relevance, the writing is on the wall: There can be only one. Quantum NP, on the other hand, is clearly the apple that fell far from the tree of NP. Two decades since the first definitions of quantum NP started rolling in, quantum complexity theorists face a stark reality: There's QMA, QCMA, QMA1, QMA(2), StoqMA, and NQP. In this article aimed at a general theoretical computer science audience, I survey these various definitions of quantum NP, their strengths and weaknesses, and why most of them, for better or worse, actually appear to fit naturally into the complexity zoo.}}, author = {{Gharibian, Sevag}}, journal = {{ACM SIGACT News}}, number = {{4}}, pages = {{54--91}}, title = {{{Guest Column: The 7 faces of quantum NP}}}, volume = {{54}}, year = {{2024}}, } @inproceedings{32407, abstract = {{Estimating the ground state energy of a local Hamiltonian is a central problem in quantum chemistry. In order to further investigate its complexity and the potential of quantum algorithms for quantum chemistry, Gharibian and Le Gall (STOC 2022) recently introduced the guided local Hamiltonian problem (GLH), which is a variant of the local Hamiltonian problem where an approximation of a ground state is given as an additional input. Gharibian and Le Gall showed quantum advantage (more precisely, BQP-completeness) for GLH with $6$-local Hamiltonians when the guiding vector has overlap (inverse-polynomially) close to 1/2 with a ground state. In this paper, we optimally improve both the locality and the overlap parameters: we show that this quantum advantage (BQP-completeness) persists even with 2-local Hamiltonians, and even when the guiding vector has overlap (inverse-polynomially) close to 1 with a ground state. Moreover, we show that the quantum advantage also holds for 2-local physically motivated Hamiltonians on a 2D square lattice. This makes a further step towards establishing practical quantum advantage in quantum chemistry.}}, author = {{Gharibian, Sevag and Hayakawa, Ryu and Gall, François Le and Morimae, Tomoyuki}}, booktitle = {{Proceedings of the 50th EATCS International Colloquium on Automata, Languages and Programming (ICALP)}}, number = {{32}}, pages = {{1--19}}, title = {{{Improved Hardness Results for the Guided Local Hamiltonian Problem}}}, doi = {{10.4230/LIPIcs.ICALP.2023.32}}, volume = {{261}}, year = {{2023}}, } @unpublished{48502, abstract = {{The prediction of photon echoes is an important technique for gaining an understanding of optical quantum systems. However, this requires a large number of simulations with varying parameters and/or input pulses, which renders numerical studies expensive. This article investigates how we can use data-driven surrogate models based on the Koopman operator to accelerate this process. In order to be successful, we require a model that is accurate over a large number of time steps. To this end, we employ a bilinear Koopman model using extended dynamic mode decomposition and simulate the optical Bloch equations for an ensemble of inhomogeneously broadened two-level systems. Such systems are well suited to describe the excitation of excitonic resonances in semiconductor nanostructures, for example, ensembles of semiconductor quantum dots. We perform a detailed study on the required number of system simulations such that the resulting data-driven Koopman model is sufficiently accurate for a wide range of parameter settings. We analyze the L2 error and the relative error of the photon echo peak and investigate how the control positions relate to the stabilization. After proper training, the dynamics of the quantum ensemble can be predicted accurately and numerically very efficiently by our methods.}}, author = {{Peitz, Sebastian and Hunstig, Anna and Rose, Hendrik and Meier, Torsten}}, title = {{{Accelerating the analysis of optical quantum systems using the Koopman operator}}}, year = {{2023}}, }