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Hybrid Confinement Techniques for Polariton Simulators
Authors
J. Düreth, P. Gagel, D. Laibacher, O. Egorov, S. Widmann, S. Betzold, M. Emmerling, S. Dam, A. Landry, C. Mayer, M. Kamp, A. Woyciechowska, B. Piętka, U. Peschel, S. Höfling, S. Klembt
Year of publication
Published in:
Nano letters: a journal dedicated to nanoscience and nanotechnology
Exciton-polariton III–V semiconductor microcavities provide a robust platform for emulating complex Hamiltonians, enabling topological photonics and quantum simulation for advanced photonic functionalities. Here, we introduce two novel fabrication techniques, etch-and-oversputter and deposit-and-oversputter, that overcome limitations of traditional photonic confinement. Both use structured, locally elongated semiconductor cavities to create deep, highly controllable potentials, while leveraging high-quality GaAs-based materials, which achieve excellent Q-factors. A sputtered all-dielectric top mirror introduces an innovative hybrid approach, simplifying fabrication while maintaining quality compared to deep ion etching. Utilizing a Kagome lattice as a benchmark, we show high-quality optical band structures previously inaccessible with deep etching. Furthermore, we study a two-dimensional breathing Kagome lattice and demonstrate polariton lasing from a zero-dimensional corner mode, confirming precise control over couplings and tight polariton localization. These methods enable fabrication of intricate lattices, including higher-order topological insulators, or on-chip quantum regimes utilizing the polariton blockade mechanism due to tight photonic confinement.
Modeling high-order harmonic generation in quantum dots using a real-space tight-binding approach
Authors
M. Thümmler, A. Croy, U. Peschel, S. Gräfe
Year of publication
Published in:
The Journal of Chemical Physics : JCP
Recently, the size-dependence of high-order harmonic generation (HHG) in quantum dots (QDs) has been investigated experimentally. In particular, for longer driving wavelengths and quantum dots smaller than 3 nm, HHG was strongly suppressed; however, there is no computational model capable of describing the strong-field response of such systems. In this work, we introduce a computationally efficient three-dimensional real-space tight-binding model specifically designed for the simulation of HHG in confined systems. The model parameters are meticulously derived from density functional theory calculations for the semiconductor bulk, followed by a process of Wannierization. Our findings demonstrate that the proposed model accurately captures the observed dependency of the HHG yield on the quantum dot size. In addition, we simulate the HHG yield for elliptically polarized pulses for different QD-sizes and driving wavelengths up to 5 μm. The proposed model fills the theoretical void in simulating HHG within medium-sized nanostructures, which cannot be described by methods applied for periodic solids, or small molecules or atoms.
Real-time simulations of laser-induced electron excitations in crystalline ZnO
Authors
X. Chen, T. Lettau, U. Peschel, N. Tancogne-Dejean, S. Botti
Year of publication
Published in:
Physical Review B
We investigate nonequilibrium electron dynamics in crystalline ZnO induced by ultrashort, relatively intense, infrared laser pulses. Our focus is on understanding the mechanism that facilitates efficient conduction band population in ZnO to enable optically pumped lasing. We consider two different pulse frequencies (in the near infrared and mid infrared) for which experimental data are available, and we calculate the electronic response of a ZnO crystal for a wide range of pulse intensities. We apply and compare three complementary theoretical approaches: the analytical Keldysh model, the numerical solution of the semiconductor Bloch equations, and real-time time-dependent density functional theory. We conclude that time-dependent density functional theory is a valid ab initio approach for predicting conduction band population, that offers an accurate enough description of static and transient optical properties of solids and provides physics insight into the intermediate excitation regime, where electronic excitations are determined by the interplay of intraband tunneling, a consequence of band bending, and interband multiphoton absorption.
Semiconductor Bloch equations in Wannier gauge with well-behaved dephasing
Authors
M. Thümmler, T. Lettau, A. Croy, U. Peschel, S. Gräfe
Year of publication
Published in:
Computer physics communications: an international journal devoted to computational physics and computer programs in physics
The semiconductor Bloch equations (SBEs) with a dephasing operator for the microscopic polarizations are a well established approach to simulate high-harmonic spectra in solids. We discuss the impact of the dephasing operator on the stability of the numerical integration of the SBEs in the Wannier gauge. It is shown that the commonly used phenomenological approach to apply dephasing is ill-defined in the presence of band crossings and leads to artifacts in the carrier distribution. They are caused by rapid changes of the dephasing operator matrix elements in the Wannier gauge, which render the convergence of the simulation in the stationary basis infeasible. In the comoving basis, also called Houston basis, these rapid changes can be resolved, but only at the cost of a largely increased computation time. As a remedy, we propose a modification of the dephasing operator with reduced magnitude in energetically close subspaces. This approach removes the artifacts in the carrier distribution and significantly speeds up the calculations, while affecting the high-harmonic spectrum only marginally. To foster further development, we provide our parallelized source code.
Probing Ultrafast Coherent Bandgap Modulation in Monolayer WSe₂ by Nonlinear Optics
Authors
S. Klimmer, T. Lettau, L. Molina, D. Kartashov, U. Peschel, J. Wilhelm, D. Neshev, G. Soavi
Year of publication
Published in:
Advanced Optical Materials
Light-matter interactions are powerful tools that seamlessly allow both functionalities of sizeable bandgap modulation and non-invasive spectroscopy. While the border between modulation and detection is often assumed to be sharp and well-defined, there are experiments where the boundaries fade. Here, the interplay between bandgap modulation and non-invasive spectroscopy is measured and explained in the case of resonant perturbative nonlinear optics in an atomically thin direct gap semiconductor.A clear deviation from the typical quadratic power scaling of second-harmonic generation near an exciton resonance is reported, and this unusual result is explained based on all-optical modulation driven by the intensity-dependent optical Stark and Bloch–Siegert shifts in the ±K valleys of the Brillouin zone. The experimental results are corroborated by analytical and numerical analysis based on the semiconductor Bloch equations, from which the resonant transition dipole moments and dephasing times of the sample are extracted. These findings redefine the meaning of perturbative nonlinear optics by revealing how coherent light-matter interactions can modify the band structure of a crystal, even in the weak-field regime. Furthermore, the results strengthen the understanding of ultrafast all-optical control of electronic states in 2D materials, with potential applications in valleytronics, Floquet engineering, and light-wave electronics.
Three-dimensional Antimony Sulfide Based Flat Optics
Authors
W. Wang, U. Hübner, A. Gärtner, T. Chen, J. Köbel, F. Jahn, D. Repp, A. Dey, H. Schneidwind, A. Dellith, J. Dellith, T. Wieduwilt, M. Zeisberger, T. Shaik, A. Bingel, M. Schmidt, J. Huang, U. Peschel, V. Deckert
Year of publication
Published in:
Advanced functional materials: full papers, feature articles, highlights
Fabricating high-index materials with designed three-dimensional (3D) micro optical elements is a challenging yet exciting area of research. Here, we develop an approach to 3D print high-index nanostructures of antimony trisulfide (Sb₂S₃) using grayscale electron beam lithography (g-EBL). A key advantage of our approach is its simplicity compared to the conventional complex EBL-based metalens fabrication process. The refractive index of Sb₂S₃ films is precisely determined using a computational genetic algorithm and the transfer matrix method. The Sb₂S₃ structures show high fidelity and reproducibility, with the refractive index being tunable through thermal treatment. We demonstrate the fabrication and performance of 3D Fresnel Zone Plates (FZPs) and metalenses with the same design specification. Theoretical and experimental evaluation confirmed the diffraction-limited capability of as-fabricated 3D optical elements and indicates that the focusing efficiency of FZPs is higher compared to metalenses. This work advances the application of Sb₂S₃ in micro- and nanoscale photonics, highlighting its potential for dynamic optical devices with precise control over output properties.
Progress in integrated and fiber optics for time-bin based quantum information processing
Authors
N. Montaut, A. George, M. Monika, F. Nosrati, H. Yu, S. Sciara, B. Crockett, U. Peschel, Z. Wang, R. Lo Franco, M. Chemnitz, W. Munro, D. Moss, J. Azaña, R. Morandotti
Year of publication
Published in:
Advanced optical technologies
The development of integrated photonic systems, both on-chip and fiber-based, has transformed quantum photonics by replacing bulky, fragile free-space optical setups with compact, efficient, and robust circuits. Photonic platforms incorporating fiber-connected sources of correlated and entangled photon pairs offer practical advantages, such as operation at room temperature, efficient integration with telecom infrastructure, and compatibility with mature and efficient semiconductor fabrication processes for cost-effective and large-scale optical circuits. The stability and scalability of integrated quantum photonics platforms have facilitated the generation and processing of quantum information in the temporal domain within a single spatial mode. Time-bin encoded states, known for their robustness against decoherence and compatibility with existing fiber-optic infrastructure, have shown to be an efficient paradigm for advanced applications like quantum secure communication, information processing, spectroscopy, imaging, and sensing. This review examines recent advancements in fiber- and chip-based platforms for generating non-classical states and their applications as quantum state processors in the time domain. We discuss the generation of pulsed quantum frequency combs using microring resonators and intra-cavity mode-locked laser schemes, enabling co- and cross-polarized quantum photonic states. Additionally, the versatility of these resonator chips for entanglement generation is emphasized, including two- and multi-photon time-bin entangled schemes. We highlight the development of time-bin entanglement analyzers in fiber architectures, featuring ultrahigh stability and post-selection-free capabilities, which enable precise and efficient characterization of two- and higher-dimensional time-bin entanglement. We also review scalable on-chip schemes for quantum key distribution, demonstrating low quantum bit error rates and compatibility with higher-dimensional quantum communication protocols. Further, methods for enhancing temporal resolution in detection schemes, crucial for time-bin encoding, are presented, such as the time-stretch sampling technique using electro-optic modulation. These innovations, relying on readily available, telecom-based fiber-optic components, provide practical, scalable, and cost-effective solutions for advancing quantum photonic technologies. Looking forward, time-bin encoding is expected to play a pivotal role in the advancement of quantum repeaters, distributed quantum networks, and hybrid light-matter systems, advancing the realization of globally scalable quantum technologies.
Topologically Tunable Polaritons Based on a Two-Dimensional Crystal in a Photonic Lattice
Authors
L. Lackner, O. Egorov, A. Ernzerhof, C. Bennenhei, V. Mitryakhin, G. Leibeling, F. Eilenberger, S. Tongay, U. Peschel, M. Esmann, C. Schneider
Year of publication
Published in:
Physical Review Letters
Structured optical cavities have advanced as a powerful test bed to study lattice Hamiltonians in general, and topological phenomena in particular. The in situ tuning of topological modes, enabled via substantial modifications of emulated lattice potentials, has remained out of experimental reach due to the commonly utilized monolithic cavity samples. Here, we study the Su-Schrieffer-Heeger (SSH) lattice Hamiltonian, which we emulate in a widely tunable open optical cavity strongly coupled to excitons in an integrated WS_{2} monolayer. The potential landscape comprises a topological domain boundary hosting a topological, exponentially localized mode at the interface between two lattices characterized by different Zak phases. The mode is spectrally tunable over 80 meV. Moreover, we use the unique tilt tunability of our implementation to transform the SSH lattice into a Stark ladder. This transformation couples the topologically protected defect mode to propagating lattice modes and effectively changes the symmetry of the system. Furthermore, it allows us to directly quantify the Zak-phase difference Δ_{Zak}=(1.07±0.11)π between the two topological phases. Our Letter constitutes an important step toward in situ tuning topological lattices to control and guide light on nonlinear chips.
