@article{57743, author = {{Krishnaswamy, Suchitra and Schlue, Fabian and Ares, L. and Dyachuk, V. and Stefszky, Michael and Brecht, Benjamin and Silberhorn, Christine and Sperling, Jan}}, issn = {{2469-9926}}, journal = {{Physical Review A}}, number = {{2}}, publisher = {{American Physical Society (APS)}}, title = {{{Experimental retrieval of photon statistics from click detection}}}, doi = {{10.1103/physreva.110.023717}}, volume = {{110}}, year = {{2024}}, } @article{58092, author = {{Carr, Alex D. and Ruppert, Claudia and Samusev, Anton K. and Magnabosco, Giulia and Vogel, Nicolas and Linnik, Tetiana L. and Rushforth, Andrew W. and Bayer, Manfred and Scherbakov, Alexey V. and Akimov, Andrey V. }}, journal = {{ACS Photonics}}, number = {{3}}, title = {{{Enhanced Photon–Phonon Interaction in WSe2 Acoustic Nanocavities}}}, doi = {{10.1021/acsphotonics.3c01601}}, volume = {{11}}, year = {{2024}}, } @article{61251, abstract = {{We theoretically investigate strategies for the deterministic creation of trains of time-bin entangled photons using an individual quantum emitter described by a Λ-type electronic system. We explicitly demonstrate the theoretical generation of linear cluster states with substantial numbers of entangled photonic qubits in full microscopic numerical simulations. The underlying scheme is based on the manipulation of ground state coherences through precise optical driving. One important finding is that the most easily accessible quality metrics, the achievable rotation fidelities, fall short in assessing the actual quantum correlations of the emitted photons in the face of losses. To address this, we explicitly calculate stabilizer generator expectation values as a superior gauge for the quantum properties of the generated many-photon state. With widespread applicability in other emitter and excitation–emission schemes also, our work lays the conceptual foundations for an in-depth practical analysis of time-bin entanglement based on full numerical simulations with predictive capabilities for realistic systems and setups, including losses and imperfections. The specific results shown in the present work illustrate that with controlled minimization of losses and realistic system parameters for quantum-dot type systems, useful linear cluster states of significant lengths can be generated in the calculations, discussing the possibility of scalability for quantum information processing endeavors.}}, author = {{Bauch, David and Köcher, Nikolas and Heinisch, Nils and Schumacher, Stefan}}, issn = {{2835-0103}}, journal = {{APL Quantum}}, number = {{3}}, publisher = {{AIP Publishing}}, title = {{{Time-bin entanglement in the deterministic generation of linear photonic cluster states}}}, doi = {{10.1063/5.0214197}}, volume = {{1}}, year = {{2024}}, } @article{61253, abstract = {{In the SUPER scheme (Swing-UP of the quantum EmitteR population), excitation of a quantum emitter is achieved with two off-resonant, red-detuned laser pulses. This allows the generation of high-quality single photons without the need of complex laser stray light suppression or careful spectral filtering. In the present work, we extend this promising method to quantum emitters, specifically semiconductor quantum dots, inside a resonant optical cavity. A significant advantage of the SUPER scheme is identified in that it eliminates re-excitation of the quantum emitter by suppressing photon emission during the excitation cycle. This, in turn, leads to almost ideal single-photon purity, overcoming a major factor typically limiting the quality of photons generated with quantum emitters in high-quality cavities. We further find that for cavity-mediated biexciton emission of degenerate photon pairs, the SUPER scheme leads to near-perfect biexciton initialization with very high values of polarization entanglement of emitted photon pairs. Published by the American Physical Society 2024 }}, author = {{Heinisch, Nils and Köcher, Nikolas and Bauch, David and Schumacher, Stefan}}, issn = {{2643-1564}}, journal = {{Physical Review Research}}, number = {{1}}, publisher = {{American Physical Society (APS)}}, title = {{{Swing-up dynamics in quantum emitter cavity systems: Near ideal single photons and entangled photon pairs}}}, doi = {{10.1103/physrevresearch.6.l012017}}, volume = {{6}}, year = {{2024}}, } @article{61255, abstract = {{Abstract Topological states have been widely investigated in different types of systems and lattices. In the present work, we report on topological edge states in double-wave (DW) chains, which can be described by a generalized Aubry-André-Harper (AAH) model. For the specific system of a driven-dissipative exciton polariton system we show that in such potential chains, different types of edge states can form. For resonant optical excitation, we further find that the optical nonlinearity leads to a multistability of different edge states. This includes topologically protected edge states evolved directly from individual linear eigenstates as well as additional edge states that originate from nonlinearity-induced localization of bulk states. Extending the system into two dimensions (2D) by stacking horizontal DW chains in the vertical direction, we also create 2D multi-wave lattices. In such 2D lattices multiple Su–Schrieffer–Heeger (SSH) chains appear along the vertical direction. The combination of DW chains in the horizonal and SSH chains in the vertical direction then results in the formation of higher-order topological insulator corner states. Multistable corner states emerge in the nonlinear regime.}}, author = {{Schneider, Tobias and Gao, Wenlong and Zentgraf, Thomas and Schumacher, Stefan and Ma, Xuekai}}, issn = {{2192-8614}}, journal = {{Nanophotonics}}, number = {{4}}, pages = {{509--518}}, publisher = {{Walter de Gruyter GmbH}}, title = {{{Topological edge and corner states in coupled wave lattices in nonlinear polariton condensates}}}, doi = {{10.1515/nanoph-2023-0556}}, volume = {{13}}, year = {{2024}}, } @article{61257, abstract = {{Exceptional points (EPs), with their intriguing spectral topology, have attracted considerable attention in a broad range of physical systems, with potential sensing applications driving much of the present research in this field. Here, we investigate spectral topology and EPs in systems with significant nonlinearity, exemplified by a nonequilibrium exciton-polariton condensate. With the possibility to control loss and gain and nonlinearity by optical means, this system allows for a comprehensive analysis of the interplay of nonlinearities (Kerr type and saturable gain) and non-Hermiticity. Not only do we find that EPs can be intentionally shifted in parameter space by the saturable gain, but we also observe intriguing rotations and intersections of Riemann surfaces and find nonlinearity-enhanced sensing capabilities. With this, our results illustrate the potential of tailoring spectral topology and related phenomena in non-Hermitian systems by nonlinearity. Published by the American Physical Society 2024 }}, author = {{Wingenbach, Jan and Schumacher, Stefan and Ma, Xuekai}}, issn = {{2643-1564}}, journal = {{Physical Review Research}}, number = {{1}}, publisher = {{American Physical Society (APS)}}, title = {{{Manipulating spectral topology and exceptional points by nonlinearity in non-Hermitian polariton systems}}}, doi = {{10.1103/physrevresearch.6.013148}}, volume = {{6}}, year = {{2024}}, } @article{61357, author = {{Krenz, Marvin and Sanna, Simone and Gerstmann, Uwe and Schmidt, Wolf Gero}}, issn = {{1932-7447}}, journal = {{The Journal of Physical Chemistry C}}, number = {{41}}, pages = {{17774--17778}}, publisher = {{American Chemical Society (ACS)}}, title = {{{Understanding and Improving Triplet Exciton Transfer in Sensitized Silicon Solar Cells}}}, doi = {{10.1021/acs.jpcc.4c05446}}, volume = {{128}}, year = {{2024}}, } @inbook{62916, author = {{Zhang, Hongdan and Zuo, Ruixin and Yang, Shidong and Trautmann, Alexander and Song, Xiaohong and Meier, Torsten and Yang, Weifeng}}, booktitle = {{High-Order Harmonic Generation in Solids}}, isbn = {{9789811279553}}, publisher = {{WORLD SCIENTIFIC}}, title = {{{Analyzing High-Order Harmonic Generation in Solids Based on Semi-Classical Recollision Models}}}, doi = {{10.1142/9789811279560_0006}}, year = {{2024}}, } @inbook{62917, author = {{Reichelt, Matthias and Zuo, Ruixin and Song, Xiaohong and Yang, Weifeng and Meier, Torsten}}, booktitle = {{High-Order Harmonic Generation in Solids}}, isbn = {{9789811279553}}, publisher = {{WORLD SCIENTIFIC}}, title = {{{High-Order Harmonic Generation in Semiconductors with Excitonic Effects}}}, doi = {{10.1142/9789811279560_0009}}, year = {{2024}}, } @article{60581, abstract = {{Abstract The natural band alignments between indium phosphide and the main dioxides of titanium, i.e. rutile, anatase, and brookite as well as amorphous titania are calculated from the branch-point energies of the respective materials. Irrespective of the titania polymorph considered, type-I band alignment is predicted. This may change, however, in dependence on the microscopic interface structure: supercell calculations for amorphous titania grown on P-rich InP(001) surfaces result in a titania conduction band that nearly aligns with that of InP. Depending on the interface specifics, both type-I band and type-II band alignments are observed in the simulations. This agrees with recent experimental findings.}}, author = {{Ruiz Alvarado, Isaac Azahel and Dreßler, Christian and Schmidt, Wolf Gero}}, issn = {{0953-8984}}, journal = {{Journal of Physics: Condensed Matter}}, number = {{7}}, publisher = {{IOP Publishing}}, title = {{{Band alignment at InP/TiO2 interfaces from density-functional theory}}}, doi = {{10.1088/1361-648x/ad9725}}, volume = {{37}}, year = {{2024}}, } @article{54868, abstract = {{AbstractMost properties of solid materials are defined by their internal electric field and charge density distributions which so far are difficult to measure with high spatial resolution. Especially for 2D materials, the atomic electric fields influence the optoelectronic properties. In this study, the atomic‐scale electric field and charge density distribution of WSe2 bi‐ and trilayers are revealed using an emerging microscopy technique, differential phase contrast (DPC) imaging in scanning transmission electron microscopy (STEM). For pristine material, a higher positive charge density located at the selenium atomic columns compared to the tungsten atomic columns is obtained and tentatively explained by a coherent scattering effect. Furthermore, the change in the electric field distribution induced by a missing selenium atomic column is investigated. A characteristic electric field distribution in the vicinity of the defect with locally reduced magnitudes compared to the pristine lattice is observed. This effect is accompanied by a considerable inward relaxation of the surrounding lattice, which according to first principles DFT calculation is fully compatible with a missing column of Se atoms. This shows that DPC imaging, as an electric field sensitive technique, provides additional and remarkable information to the otherwise only structural analysis obtained with conventional STEM imaging.}}, author = {{Groll, Maja and Bürger, Julius and Caltzidis, Ioannis and Jöns, Klaus D. and Schmidt, Wolf Gero and Gerstmann, Uwe and Lindner, Jörg K. N.}}, issn = {{1613-6810}}, journal = {{Small}}, publisher = {{Wiley}}, title = {{{DFT‐Assisted Investigation of the Electric Field and Charge Density Distribution of Pristine and Defective 2D WSe2 by Differential Phase Contrast Imaging}}}, doi = {{10.1002/smll.202311635}}, year = {{2024}}, } @article{54856, abstract = {{Abstract Theoretical spectroscopy based on double perturbation theory is typically challenged by systems with large orbital hyperfine splitting. Therefore, we here derive a rigorous, non-perturbative scheme starting from Dirac’s equation which allows to calculate the contribution of the orbital HFI for complex structures including heavy atoms with strong spin-orbit coupling (SOC). Using the PAW formalism, the method has been implemented in the software package Quantum ESPRESSO. We show that the ‘orbital part’ actually scales with SOC strength if orbital quenching is hindered by low local symmetry, i.e. in case of dimers or atoms at surfaces. This holds true in particular when the unpaired electron is localized in quasi-atomic p-like orbitals. Here, the orbital part is by far not negligible, but becomes dominant by surpassing the dipolar contribution by a factor of five.}}, author = {{Franzke, Katharina and Schmidt, Wolf Gero and Gerstmann, Uwe}}, issn = {{1742-6588}}, journal = {{Journal of Physics: Conference Series}}, number = {{1}}, publisher = {{IOP Publishing}}, title = {{{Relativistic calculation of the orbital hyperfine splitting in complex microscopic structures}}}, doi = {{10.1088/1742-6596/2701/1/012094}}, volume = {{2701}}, year = {{2024}}, } @article{54865, author = {{Krenz, Marvin and Gerstmann, Uwe and Schmidt, Wolf Gero}}, issn = {{0031-9007}}, journal = {{Physical Review Letters}}, number = {{7}}, publisher = {{American Physical Society (APS)}}, title = {{{Defect-Assisted Exciton Transfer across the Tetracene-Si(111):H Interface}}}, doi = {{10.1103/physrevlett.132.076201}}, volume = {{132}}, year = {{2024}}, } @article{62868, abstract = {{We theoretically investigate strategies for the deterministic creation of trains of time-bin entangled photons using an individual quantum emitter described by a Λ-type electronic system. We explicitly demonstrate the theoretical generation of linear cluster states with substantial numbers of entangled photonic qubits in full microscopic numerical simulations. The underlying scheme is based on the manipulation of ground state coherences through precise optical driving. One important finding is that the most easily accessible quality metrics, the achievable rotation fidelities, fall short in assessing the actual quantum correlations of the emitted photons in the face of losses. To address this, we explicitly calculate stabilizer generator expectation values as a superior gauge for the quantum properties of the generated many-photon state. With widespread applicability in other emitter and excitation–emission schemes also, our work lays the conceptual foundations for an in-depth practical analysis of time-bin entanglement based on full numerical simulations with predictive capabilities for realistic systems and setups, including losses and imperfections. The specific results shown in the present work illustrate that with controlled minimization of losses and realistic system parameters for quantum-dot type systems, useful linear cluster states of significant lengths can be generated in the calculations, discussing the possibility of scalability for quantum information processing endeavors.}}, author = {{Bauch, David and Köcher, Nikolas and Heinisch, Nils and Schumacher, Stefan}}, issn = {{2835-0103}}, journal = {{APL Quantum}}, number = {{3}}, publisher = {{AIP Publishing}}, title = {{{Time-bin entanglement in the deterministic generation of linear photonic cluster states}}}, doi = {{10.1063/5.0214197}}, volume = {{1}}, year = {{2024}}, } @article{62853, abstract = {{Abstract Developing coherent excitation methods for quantum emitters ensuring high brightness, optimal single‐photon purity and indistinguishability of the emitted photons has been a key challenge in the past years. While various methods have been proposed and explored, they all have specific advantages and disadvantages. This study investigates the dynamics of the recent swing‐up scheme as an excitation method for a two‐level system and its performance in single‐photon generation. By applying two far red‐detuned laser pulses, the two‐level system can be prepared in the excited state with near‐unity fidelity. The successful operation and coherent character of this technique are demonstrated using a semiconductor quantum dot (QD). Moreover, the multi‐dimensional parameter space of the two laser pulses is explored to analyze its impact on excitation fidelity. Finally, the performance of the scheme as an excitation method for generating high‐quality single photons is analyzed. The swing‐up scheme itself proves effective, exhibiting nearly perfect single‐photon purity, while the observed indistinguishability in the studied sample is limited by the influence of the inevitable high excitation powers on the semiconductor environment of the quantum dot.}}, author = {{Boos, Katarina and Sbresny, Friedrich and Kim, Sang Kyu and Kremser, Malte and Riedl, Hubert and Bopp, Frederik W. and Rauhaus, William and Scaparra, Bianca and Jöns, Klaus and Finley, Jonathan J. and Müller, Kai and Hanschke, Lukas}}, issn = {{2511-9044}}, journal = {{Advanced Quantum Technologies}}, number = {{4}}, publisher = {{Wiley}}, title = {{{Coherent Swing‐Up Excitation for Semiconductor Quantum Dots}}}, doi = {{10.1002/qute.202300359}}, volume = {{7}}, year = {{2024}}, } @unpublished{62858, abstract = {{Phonons in solid-state quantum emitters play a crucial role in their performance as photon sources in quantum technology. For resonant driving, phonons dampen the Rabi oscillations resulting in reduced preparation fidelities. The phonon spectral density, which quantifies the strength of the carrier-phonon interaction, is non-monotonous as a function of energy. As one of the most prominent consequences, this leads to the reappearance of Rabi rotations for increasing pulse power, which was theoretically predicted in Phys. Rev. Lett. 98, 227403 (2007). In this paper we present the experimental demonstration of the reappearance of Rabi rotations.}}, author = {{Hanschke, L. and Bracht, T. K. and Schöll, E. and Bauch, David and Berger, Eva and Kallert, Patricia and Peter, M. and Garcia, A. J. and Silva, S. F. Covre da and Manna, S. and Rastelli, A. and Schumacher, Stefan and Reiter, D. E. and Jöns, Klaus}}, booktitle = {{arXiv:2409.19167}}, title = {{{Experimental measurement of the reappearance of Rabi rotations in semiconductor quantum dots}}}, year = {{2024}}, } @unpublished{62856, abstract = {{On-chip emitters that can generate single and entangled photons are essential building blocks for developing photonic quantum information processing technologies in a scalable fashion. Semiconductor quantum dots (QDs) are attractive candidates that emit high-quality quantum states of light on demand, however at a rate limited by their spontaneous radiative lifetime. In this study, we utilize the Purcell effect to demonstrate up to a 38-fold enhancement in the emission rate of InAs QDs by coupling them to metal-clad GaAs nanopillars. These cavities, featuring a sub-wavelength mode volume of 4.5x10-4 (λ/n)3 and low quality factor of 62, enable Purcell-enhanced single-photon emission across a large bandwidth of 15 nm. The broadband nature of the cavity eliminates the need for implementing tuning mechanisms typically required to achieve QD-cavity resonance, thus relaxing fabrication constraints. Ultimately, this QD-cavity architecture represents a significant stride towards developing solid-state quantum emitters generating near-ideal single-photon states at GHz-level repetition rates.}}, author = {{Jöns, Klaus}}, title = {{{Purcell-enhanced single-photon emission from InAs/GaAs quantum dots coupled to broadband cylindrical nanocavities}}}, year = {{2024}}, } @article{49117, author = {{Scharwald, D. and Meier, T. and Sharapova, P. R.}}, issn = {{2643-1564}}, journal = {{Physical Review Research}}, keywords = {{General Physics and Astronomy}}, number = {{4}}, publisher = {{American Physical Society (APS)}}, title = {{{Phase sensitivity of spatially broadband high-gain SU(1,1) interferometers}}}, doi = {{10.1103/physrevresearch.5.043158}}, volume = {{5}}, year = {{2023}}, } @article{48599, abstract = {{AbstractThe biexciton‐exciton emission cascade commonly used in quantum‐dot systems to generate polarization entanglement yields photons with intrinsically limited indistinguishability. In the present work, it focuses on the generation of pairs of photons with high degrees of polarization entanglement and simultaneously high indistinguishability. It achieves this goal by selectively reducing the biexciton lifetime with an optical resonator. It demonstrates that a suitably tailored circular Bragg reflector fulfills the requirements of sufficient selective Purcell enhancement of biexciton emission paired with spectrally broad photon extraction and twofold degenerate optical modes. The in‐depth theoretical study combines (i) the optimization of realistic photonic structures solving Maxwell's equations from which model parameters are extracted as input for (ii) microscopic simulations of quantum‐dot cavity excitation dynamics with full access to photon properties. It reports non‐trivial dependencies on system parameters and use the predictive power of the combined theoretical approach to determine the optimal range of Purcell enhancement that maximizes indistinguishability and entanglement to near unity values, here specifically for the telecom C‐band at 1550 nm.}}, author = {{Bauch, David and Siebert, Dustin and Jöns, Klaus and Förstner, Jens and Schumacher, Stefan}}, issn = {{2511-9044}}, journal = {{Advanced Quantum Technologies}}, keywords = {{tet_topic_qd}}, publisher = {{Wiley}}, title = {{{On‐Demand Indistinguishable and Entangled Photons Using Tailored Cavity Designs}}}, doi = {{10.1002/qute.202300142}}, year = {{2023}}, } @unpublished{43246, abstract = {{The biexciton-exciton emission cascade commonly used in quantum-dot systems to generate polarization entanglement yields photons with intrinsically limited indistinguishability. In the present work we focus on the generation of pairs of photons with high degrees of polarization entanglement and simultaneously high indistinguishibility. We achieve this goal by selectively reducing the biexciton lifetime with an optical resonator. We demonstrate that a suitably tailored circular Bragg reflector fulfills the requirements of sufficient selective Purcell enhancement of biexciton emission paired with spectrally broad photon extraction and two-fold degenerate optical modes. Our in-depth theoretical study combines (i) the optimization of realistic photonic structures solving Maxwell's equations from which model parameters are extracted as input for (ii) microscopic simulations of quantum-dot cavity excitation dynamics with full access to photon properties. We report non-trivial dependencies on system parameters and use the predictive power of our combined theoretical approach to determine the optimal range of Purcell enhancement that maximizes indistinguishability and entanglement to near unity values in the telecom C-band at $1550\,\mathrm{nm}$.}}, author = {{Bauch, David and Siebert, Dustin and Jöns, Klaus and Förstner, Jens and Schumacher, Stefan}}, keywords = {{tet_topic_phc, tet_topic_qd}}, title = {{{On-demand indistinguishable and entangled photons at telecom frequencies using tailored cavity designs}}}, year = {{2023}}, }