arXiv subjects

Stefan Schumacher

Publications and source records attributed to Stefan Schumacher.

At least 37 records · Page 2Linked to original sources

arXiv2025

Splitting spin-orbit coupled polariton vortex pairs in the non-Hermitian Rashba-Dresselhaus band at room temperature

Spin orbit coupling gives rise to intriguing physical phenomena in bosonic condensates, such as formation of stripe phases and domains with vortex arrays. However, how the non-Hermiticity affects the spatial distribution of spin orbit coupled topological defects such as vortex pair is still challenging to study. In the present work, we realize a non-equilibrium room-temperature exciton polariton condensate within a microdisk potential in a liquid crystal (LC) microcavity with the perovskite CsPbBr3 as optically active material. We use the interplay of TE-TM mode splitting and Rashba-Dresselhaus spin-orbit coupling (RDSOC) to realize electrically tunable polariton vortex pairs with locked spin and orbital angular momentum. Importantly, the non-Hermiticity of RDSOC bands leads to nonreciprocal transportation of the vortex pair such that they move to the opposite edges of the microdisk depending on their spin. Our results are robust against sample imperfections and pave the way to investigate the coupling of vortex orbital and spin degrees of freedom in a quantum fluid of light at room temperature, offering potential for generation of complex states of light for non-Hermitian quantum optical information processing within optoelectronic chips.

physics.optics↗

arXiv2025

Entanglement between dependent degrees of freedom: Quasiparticle correlations

Common notions of entanglement are based on well-separated subsystems. However, obtaining such independent degrees of freedom is not always possible because of physical constraints. In this work, we explore the notion of entanglement in the context of dependent degrees of freedom. As a physically relevant application, we specifically study quantum correlation features for quasiparticle descriptions. Those are paramount for interacting light-matter systems, utilizing excitations of fermion-boson hybrid modes. By comparing independent and dependent degrees of freedom, we uncover that certain states are nonentangled although they would be entangled when only focusing on the common, independent description, and vice versa. Therefore, insight is provided into the resourcefulness of quantum correlations within the rarely discussed context of dependent degrees of freedom for light-matter links in quantum information applications.

quant-ph↗

arXiv2025

Optically and remotely controlling localization of exciton polariton condensates in a potential lattice

Exciton polaritons are inherently tunable systems with adjustable potential landscape. In this work we show that exciton polariton condensates can be selectively localized in a fixed optically induced periodic lattice with uniform potential depth, by judiciously controlling a second focused pump of very small size away from the lattice chain. Specifically, the localized polariton condensate can be tuned among different potential traps by adjusting the relative distance between the small pump spot and the potential lattice. The adjustment of the excitation position of the smaller pump spot and its combination with the fixed larger pump spot for the potential creation induce the mode selection determined by gain profile, group velocity, and potential distribution within the system. The localization of the exciton polariton condensate and its control are independent of the orientation of the potential lattice, thus, even in slightly disordered system, one can selectively excite such localized polariton condensates. Our results illuminate a path to the remote manipulation of exciton polariton bosonic condensates in fixed integrated photonic chips and circuits.

physics.optics↗

arXiv2025

Observation of condensed moire exciton polaritons in twisted photonic lattices at room temperature

Moire lattices attract significant attention in double-layer graphene and TMD layer heterostructures as well as in photonic crystals due to the interesting exotic physics that emerges within these structures. However, direct measurement of the moiré ground, excited states and Bloch bands in twisted photonic lattices is still illusive. In this work we report strong coupling between excitons in CsPbBr3 microplates and moire photonic modes at room temperature. Depending on the coupling strength between the nearest potential sites, we observe staggered moire polariton ground states, excited states and moire polariton bands. Phase locked moire zero (in-phase) states and moire pi (antiphase) states with different spatial distributions are measured. The moire polariton distribution can be tuned into the shape of a parallelogram by controlling the depth and width of the potential in one photonic lattice with another superimposed one fixed. In addition, moire polaritons in twisted 2D honeycomb lattices are also observed. Increasing the pumping density, we realize exciton polariton condensation in the moire potential sites of the 1D/2D twisted lattices with the coherence time of around 1.4 ps. Our work lays the foundation to study coherent moire polariton condensation in twisted photonic lattices at room temperature.

physics.optics↗

arXiv2024

PHOENIX -- Paderborn highly optimized and energy efficient solver for two-dimensional nonlinear Schrödinger equations with integrated extensions

In this work, we introduce PHOENIX, a highly optimized explicit open-source solver for two-dimensional nonlinear Schrödinger equations with extensions. The nonlinear Schrödinger equation and its extensions (Gross-Pitaevskii equation) are widely studied to model and analyze complex phenomena in fields such as optics, condensed matter physics, fluid dynamics, and plasma physics. It serves as a powerful tool for understanding nonlinear wave dynamics, soliton formation, and the interplay between nonlinearity, dispersion, and diffraction. By extending the nonlinear Schrödinger equation, various physical effects such as non-Hermiticity, spin-orbit interaction, and quantum optical aspects can be incorporated. PHOENIX is designed to accommodate a wide range of applications by a straightforward extendability without the need for user knowledge of computing architectures or performance optimization. The high performance and power efficiency of PHOENIX are demonstrated on a wide range of entry-class to high-end consumer and high-performance computing GPUs and CPUs. Compared to a more conventional MATLAB implementation, a speedup of up to three orders of magnitude and energy savings of up to 99.8% are achieved. The performance is compared to a performance model showing that PHOENIX performs close to the relevant performance bounds in many situations. The possibilities of PHOENIX are demonstrated with a range of practical examples from the realm of nonlinear (quantum) photonics in planar microresonators with active media including exciton-polariton condensates. Examples range from solutions on very large grids, the use of local optimization algorithms, to Monte Carlo ensemble evolutions with quantum noise enabling the tomography of the system's quantum state.

physics.comp-ph↗

arXiv2024

Higher-order dark solitons and oscillatory dynamics in microcavity polariton condensates

Dark solitons carrying quantized phase information arouse great interest in different nonlinear systems. A dark soliton in 1D can be stabilized in microcavity polariton condensates as a confinement is imposed on it to prevent its decay. Such a confinement can be realized by optical manners, i.e., by using optically induced potential traps. Under nonresonant excitation with spatially periodically modulated optical beams, we numerically demonstrate that besides fundamental dark solitons, higher-order dark solitons with multiple density minima and $π$-phase jumps can also stably survive in the potential (pump) valleys. Simultaneously exciting several orders of dark soliton states by properly choosing the lattice constant of the optical pump gives rise to dark oscillators. In some cases, the stably trapped dark solitons in adjacent pump valleys squeeze the condensate density between them and generate another type of density dips in the pump peak area. Surprisingly, such a density dip supports another stable dark soliton with a larger size which is essentially composed of two counter-propagating gray solitons.

physics.optics↗

arXiv2024

Time-bin entanglement in the deterministic generation of linear photonic cluster states

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 also to other emitter and excitation-emission schemes, 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.

quant-ph↗

arXiv2024

Topological edge and corner states in coupled wave lattices in nonlinear polariton condensates

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 horizontal 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.

cond-mat.quant-gas↗

arXiv2024

Organic room-temperature polariton condensate in a higher-order topological lattice

Organic molecule exciton-polaritons in photonic lattices are a versatile platform to emulate unconventional phases of matter at ambient conditions, including protected interface modes in topological insulators. Here, we investigate bosonic condensation in the most prototypical higher-order topological lattice: a 2D-version of the Su-Schrieffer-Heeger (SSH) model, supporting both 0D and 1D topological modes. We study fluorescent protein-filled, structured microcavities defining a staggered photonic trapping potential and observe the resulting first- and higher-order topologically protected modes via spatially resolved photoluminescence spectroscopy. We account for the spatial mode patterns by tight-binding calculations and theoretically characterize the topological invariants of the lattice. Under strong optical pumping, we observe bosonic condensation into the topological modes. Via interferometric measurements, we map the spatial first-order coherence in the protected 1D modes extending over 10 microns. Our findings pave the way towards organic on-chip polaritonics using higher-order topology as a tool for the generation of robustly confined polaritonic lasing states.

physics.optics↗

arXiv2023

Manipulating polariton condensates by Rashba-Dresselhaus coupling at room temperature

The spin-orbit coupling plays an important role in the spin Hall effect and the topological insulators. In addition, the spin-orbit coupled Bose-Einstein condensates show remarkable quantum many-body phase transition. In this work we tune the exciton polariton condensate by virtue of the Rashba-Dresselhaus (RD) spin-orbit coupling in a liquid-crystal filled microcavity where perovskite CsPbBr3 microplates act as the gain material at room temperature. We realize an artificial gauge field on the CsPbBr3 exciton polariton condensate, which splits the condensates with opposite spins in both momentum and real spaces. Our work paves the way to manipulate the exciton polariton condensate with a synthetic gauge field based on the RD spin-orbit coupling at room temperature.

cond-mat.quant-gas↗

arXiv2023

Electrically controlling vortices in a neutral exciton polariton condensate at room temperature

Manipulating bosonic condensates with electric fields is very challenging as the electric fields do not directly interact with the neutral particles of the condensate. Here we demonstrate a simple electric method to tune the vorticity of exciton polariton condensates in a strong coupling liquid crystal (LC) microcavity with CsPbBr$_3$ microplates as active material at room temperature. In such a microcavity, the LC molecular director can be electrically modulated giving control over the polariton condensation in different modes. For isotropic non-resonant optical pumping we demonstrate the spontaneous formation of vortices with topological charges of +1, +2, -2, and -1. The topological vortex charge is controlled by a voltage in the range of 1 to 10 V applied to the microcavity sample. This control is achieved by the interplay of a built-in potential gradient, the anisotropy of the optically active perovskite microplates, and the electrically controllable LC molecular director in our system with intentionally broken rotational symmetry. Besides the fundamental interest in the achieved electric polariton vortex control at room temperature, our work paves the way to micron-sized emitters with electric control over the emitted light's phase profile and quantized orbital angular momentum for information processing and integration into photonic circuits.

physics.optics↗

arXiv2023

Photochemical reaction enabling the engineering of photonic spin-orbit coupling in organic-crystal optical microcavities

The control and active manipulation of spin-orbit coupling (SOC) in photonic systems is fundamental in the development of modern spin optics and topological photonic devices. Here, we demonstrate the control of an artificial Rashba-Dresselhaus (RD) SOC mediated by photochemical reactions in a microcavity filled with an organic single-crystal of photochromic phase-change character. Splitting of the circular polarization components of the optical modes induced by photonic RD SOC is observed experimentally in momentum space. By applying an ultraviolet light beam, we control the spatial molecular orientation through a photochemical reaction and with that we control the energies of the photonic modes. This way we realize a reversible conversion of spin-splitting of the optical modes with different energies, leading to an optically controlled switching between circularly and linearly polarized emission from our device. Our strategy of in situ and reversible engineering of SOC induced by a light field provides a promising approach to actively design and manipulate synthetic gauge fields towards future on-chip integration in photonics and topological photonic devices.

physics.optics↗

arXiv2023

Continuous-variable quantum optics and resource theory for ultrafast semiconductor spectroscopy

In this review, we discuss the use of continuous variable spectroscopy techniques for investigating quantum coherence and light-matter interactions in semiconductor systems with ultrafast dynamics. We focus on multichannel homodyne detection as a powerful tool to measure the quantum coherence and the full density matrix of a polariton system. By monitoring the temporal decay of quantum coherence in the polariton condensate, we observe coherence times exceeding the nanosecond scale. Our findings, supported by proof-of-concept experiments and numerical simulations, demonstrate the enhanced resourcefulness of the produced system states for modern quantum protocols. The combination of tailored resource quantifiers and ultrafast spectroscopy techniques presented here paves the way for future applications of quantum information technologies.

cond-mat.mes-hall↗

arXiv2023

On-demand indistinguishable and entangled photons using tailored cavity designs

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 indistinguishability. 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, here specifically for the telecom C-band at $1550\,\mathrm{nm}$.

quant-ph↗

arXiv2023

Tweaking Spectral Topology and Exceptional Points by Nonlinearity in Non-Hermitian Polariton Systems

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 theoretically demonstrate the realization of EPs in a system with significant nonlinearity, a non-equilibrium 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, we also observe intriguing rotations and intersections of Riemann surfaces, and find nonlinearity-enhanced sensing capabilities. Our results are quite general in nature and illustrate the potential of tailoring spectral topology and related phenomena in non-Hermitian systems by nonlinearity.

physics.optics↗

arXiv2023

Single-shot spatial instability and electric control of polariton condensates at room temperature

In planar microcavities, the transverse-electric and transverse-magnetic (TE-TM) mode splitting of cavity photons arises due to their different penetration into the Bragg mirrors and can result in optical spin-orbit coupling (SOC). In this work, we find that in a liquid crystal (LC) microcavity filled with perovskite microplates, the pronounced TE-TM splitting gives rise to a strong SOC that leads to the spatial instability of microcavity polariton condensates under single-shot excitation. Spatially varying hole burning and mode competition occurs between polarization components leading to different condensate profiles from shot to shot. The single-shot polariton condensates become stable when the SOC vanishes as the TE and TM modes are spectrally well separated from each other, which can be achieved by application of an electric field to our LC microcavity with electrically tunable anisotropy. Our findings are well reproduced and traced back to their physical origin by our detailed numerical simulations. With the electrical manipulation our work reveals how the shot-to-shot spatial instability of spatial polariton profiles can be engineered in anisotropic microcavities at room temperature, which will benefit the development of stable polariton-based optoeletronic and light-emitting devices.

physics.optics↗

arXiv2023

Swing-up dynamics in quantum emitter cavity systems

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 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 dots 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 the emitted photon pairs.

quant-ph↗

arXiv2022

A room-temperature electrical-field-enhanced ultrafast switch in organic microcavity polariton condensates

Integrated electro-optical switches are essential as one of the fundamental elements in the development of modern optoelectronics. As an architecture for photonic systems, exciton polaritons, that are hybrid bosonic quasiparticles that possess unique properties derived from both excitons and photons, have shown much promise. For this system, we demonstrate a significant improvement of emitted intensity and condensation threshold by applying an electric field to a microcavity filled with an organic microbelt. Our theoretical investigations indicate that the electric field makes the excitons dipolar and induces an enhancement of the exciton-polariton interaction and of the polariton lifetime. Based on these electric field induced changes, a sub-nanosecond electrical-field-enhanced polariton condensate switch is realized at room temperature, providing the basis for developing an on-chip integrated photonic device in the strong light-matter coupling regime.

physics.optics↗