arXiv subjects

Monika Emmerling

Publications and source records attributed to Monika Emmerling.

At least 19 recordsLinked to original sources

arXiv2026

Encapsulated macroscopic WS$_2$ monolayers enable room-temperature exciton-polariton lattices

Large-area, optically homogeneous monolayer semiconductors are a critical prerequisite for scalable room-temperature polaritonics and for realizing polariton lattices extending across many unit cells. Yet, the small size, optical inhomogeneity, and device-to-device variability of conventional exfoliated flakes have remained major obstacles. Here, we overcome these limitations using 1-dodecanol-encapsulated WS$_2$ monolayers that combine millimeter-scale coverage with remarkably uniform optical properties over lateral distances approaching $300\,$$\mu \mathrm{m}$. Integrated into a tunable open microcavity, these monolayers exhibit robust room-temperature exciton-photon strong coupling, evidenced by a pronounced anti-crossing and a Rabi splitting of $\hbar \Omega_{\mathrm{R}} \approx 31\,\mathrm{meV}$. Leveraging the exceptional uniformity of this platform, we realize a two-dimensional polaritonic kagome lattice and directly resolve its characteristic band structure. Angle-resolved spectroscopy reveals Dirac dispersive bands together with a weakly dispersive flat-band-like branch within the $s$-band, in good agreement with a linear non-interacting model. Complementary momentum- and real-space imaging further identifies the associated bond-centered and site-centered mode profiles. These results establish large-area WS$_2$ monolayers in open microcavities as a scalable platform for engineering polariton band structures and exploring synthetic quantum materials under ambient conditions.

cond-mat.mes-hall↗

arXiv2026

Photonic Cluster State Generation from a Quantum Dot Emitting in the Telecom C-band

Photonic cluster states are a key resource for photonic quantum information processing. So far, deterministic generation of these states has been limited to the near-infrared wavelength range. To achieve quantum advantage in communication while maintaining compatibility with silicon photonics, operation in the telecom wavelength range is required. In this work, we demonstrate deterministic cluster state generation directly in the telecom C-band. This is achieved through repetitive excitation of a hole spin confined in an indium-arsenide quantum dot subjected to an external magnetic field. We characterize the quantum process that generates the cluster state by measuring its process map, obtaining a fidelity of $\mathrm{F} = 0.71 \pm 0.01$ to the ideal case. As part of this characterization, we observe spin--photon polarization entanglement with a negativity of $\mathrm{N} = 0.27 \pm 0.02$. The emitted photons exhibit indistinguishability of at least 83%, demonstrating the potential for future fusion gates necessary for photonic cluster state generation beyond linear connectivity.

quant-ph↗

arXiv2026

Spin-momentum locking of polariton edge states in honeycomb lattices

Transverse-electric/Transverse-magnetic splitting in dielectric-mirror microcavities introduces an effective spin-orbit coupling for photons. While the bulk states remain linearly polarized, for exponentially localized edge states in a photonic lattice, this coupling induces elliptical polarization whose handedness is locked to the propagation direction, analogous to the transverse spin of evanescent electromagnetic waves. We reveal spin-momentum locking through Stokes polarimetry of zigzag edge states in a honeycomb exciton-polariton lattice. The effect persists in a stretched honeycomb supporting a photonic bandgap, where spin-polarized carrier injection enables selective lasing of either chiral edge states. Our results provide a route toward ultrafast spin-controlled unidirectional propagation in polariton systems without external magnetic fields.

cond-mat.mes-hall↗

arXiv2026

Integrated Whispering-Gallery Microlaser-Waveguide Platform for On-Chip Electrical Excitation of InGaAs Quantum Dots

We report the fabrication and characterization of an integrated quantum photonic device consisting of an electrically driven whispering-gallery-mode micropillar laser evanescently coupled to a ridge waveguide, both incorporating InGaAs quantum dots (QDs). The lasing characteristics of microlasers are systematically investigated as a function of the pillar-waveguide gap distance. Coherent emission from the whispering-gallery-mode microlaser coupled into the waveguide enables on-chip optical excitation of QDs embedded in an electrically contacted micropillar at the end of the waveguide. Under continuous-wave on-chip excitation, we observe single-photon emission with $g^{(2)}(0) = (3.49 \pm 0.01) \%$ for a QD integrated in the outcoupling micropillar which can be spectrally tuned-by the quantum confined Stark effect. These results constitute an important step toward low-footprint, deterministic, and scalable single-photon sources for QD-based integrated quantum photonic circuits.

physics.optics↗

arXiv2025

A topological field-effect memristor

Overcoming the limitations of the von Neumann architecture requires new computational paradigms capable of solving complex problems efficiently. Quantum and neuromorphic computing rely on unconventional materials and device functionalities, yet achieving resilience to imperfections and reliable operation remains a major challenge. This has motivated growing interest in topological materials that provide robust and low-power operation while preserving coherence. However, integrating coherent topological transport with non-volatile memory functionality in a single reconfigurable device has remained challenging. In this work, we demonstrate a topological field-effect memristor based on inverted InAs/GaInSb/InAs trilayer quantum wells operating in the quantum spin Hall regime. The intrinsic floating-gate behavior allows one to reconfigure the transistor functionality into memristive functionality with broad electric-field tunability. Unlike other memristor implementations, one resistance state is governed entirely by dissipationless, coherent transport through helical edge channels, while the other arises from incoherent bulk conduction. By combining electrically tunable coherent and incoherent transport with memory functionality, our device realizes a prototypical topological electronic element that integrates coherent transport and adaptive memristive behavior, paving the way for hybrid quantum-neuromorphic architectures.

cond-mat.mes-hall↗

arXiv2025

Probing Local Topology in a Disordered Higher-Order Topological Insulator

Higher-order topology is prized for its ability to realize lower-dimensional boundary states which are stable beyond fine-tuning. However, disorder presents a failure mechanism that can destroy topological in-gap states. Here, we investigate a disordered two-dimensional polariton lattice and employ the spectral localizer framework to define a real-space topological index rooted in crystalline spatial symmetries. This framework enables direct real-space mapping of topology beyond conventional momentum-space classifications, confirming the presence of corner and edge modes in this generalized Su-Schrieffer-Heeger model. Furthermore, it can directly quantify topological protection of a state. We leverage the versatility of our platform to experimentally realize normally distributed, random disorder and find that the corner states persist until the spectral gap closes. Experimentally, this corresponds to a disorder strength of approximately one quarter of the spectral gap. The spectral localizer accurately identifies the disorder strength at which the bandgap closes, establishing the framework as a predictive tool for every finite size system. Our results broaden the design principles for higher-order topological insulators and open the way towards imple menting disorder-resilient devices for robust lasing, light-routing, and quantum computation.

physics.optics↗

arXiv2025

Direct experimental access to the bulk band inversion in a topological metamaterial

Topological phases in exciton-polaritons and other metamaterial platforms have attracted significant attention due to their flexibility as Hamiltonian simulators. In previous works, signatures of topology have mainly been investigated from the perspective of edge states - strongly localised modes with exponentially decaying intensity into the bulk. While these edge states have become the hallmark of topological systems as they can facilitate non-reciprocal transport in potential applications, the topology is fundamentally encoded in the bulk band structure. In particular, the momentum-dependence of the eigenstates, i.e., the wave functions, determines the topology, usually reflected in a bulk band inversion. We present a band inversion in the paradigmatic Su-Schrieffer-Heeger (SSH) model, characterised by a reversal of the sublattice symmetry, quantified by the expectation value $\langle \sigma_\mathrm{x} \rangle$, when going from the centre of the Brillouin zone to the zone boundary. Here, we show direct experimental access to this bulk band inversion in SSH exciton-polariton chains, using two-dimensional momentum-space ($k$-space) mapping - without the need for real-space imaging. This technique enables the direct observation of the momentum-dependent inversion of the sublattice symmetry in the bulk bands, providing a unique perspective on topological phases beyond conventional edge state measurements. Our approach establishes effective momentum-resolved sublattice phase measurements as a powerful tool for accessing the wave function and bulk topology in photonic and polaritonic systems and beyond.

physics.optics↗

arXiv2025

On chip plasmonic slit cavity platform for room temperature strong coupling with deterministically positioned colloidal quantum dots

Strong coupling between quantum emitters and optical cavities is essential for quantum information processing, high-purity single-photon sources, and nonlinear quantum devices. Achieving this regime at room temperature in a compact, deterministic on-chip platform-critical for integration with nanoelectronic circuitry and scalable device architectures-remains a major challenge, mainly due to the difficulty of fabricating cavities with ultra-small mode volumes and precisely positioning quantum emitters. Here, we demonstrate a robust quantum plasmonic device in which colloidal quantum dots (Qdots) are strongly coupled to plasmonic slit cavities using a dielectrophoresis-based positioning technique with real-time photoluminescence (PL) feedback, providing directly resolvable coupled structures that enable parallel device fabrication and straightforward integration with additional optical elements such as waveguides. Our measurements reveal clear PL resolved Rabi splitting at room temperature with pre characterized cavities, with variations across devices that scale with the average number of coupled Qdots. While electrical tuning via the quantum-confined Stark effect is enabled by integrated electrodes, its impact is largely overshadowed by room-temperature spectral diffusion. Our results pave the way for scalable, electrically tunable quantum plasmonic platforms, offering new opportunities for integrated quantum photonic circuits, active light-matter interactions, and room-temperature quantum technologies.

physics.optics↗

arXiv2025

Tuning the non-linear interactions of hybrid interlayer excitons in bilayer MoS2 via electric fields

Hybrid interlayer excitons in bilayer MoS2 are a promising platform for nonlinear optics due to their intrinsic dipolar character, which combines in-plane and out-ofplane dipole moments. In this work, we directly probe the nonlinear exciton-exciton interactions of hybrid interlayer excitons. By applying an external out-of-plane electric field, we polarize the excitons to enhance their mutual dipolar interactions, thereby deliberately favoring these repulsive contributions over competing attractive manybody corrections. We furthermore establish a fully microscopic theoretical description of these effects to explain the core experimental results. The tuning results in a significantly larger blueshift compared to the zero-field case and perspectively opens an avenue to even switch between repulsive and attractive interaction potentials. Our findings establish that strong nonlinearities can be tuned via an external electric field, providing a new degree of control over exciton interactions beyond density tuning alone.

cond-mat.mtrl-sci↗

arXiv2025

Quantum spin Hall effect in III-V semiconductors at elevated temperatures: advancing topological electronics

The quantum spin Hall effect (QSHE), a hallmark of topological insulators, enables dissipationless, spin-polarized edge transport and has been predicted in various two-dimensional materials. However, challenges such as limited scalability, low-temperature operation, and the lack of robust electronic transport have hindered practical implementations. Here, we demonstrate the QSHE in an InAs/GaInSb/InAs trilayer quantum well structure operating at elevated temperatures. This platform meets key criteria for device integration, including scalability, reproducibility, and tunability via electric field. When the Fermi level is positioned within the energy gap, we observe quantized resistance values independent of device length and in both local and nonlocal measurement configurations, confirming the QSHE. Helical edge transport remains stable up to T = 60 K, with further potential for higher-temperature operation. Our findings establish the InAs/GaInSb system as a promising candidate for integration into next-generation devices harnessing topological functionalities, advancing the development of topological electronics.

cond-mat.mes-hall↗

arXiv2025

Electrical Control of Excitons in Bare-MoSe2 and MoSe2/NbSe2 Heterostructure

Monolayer transition metal dichalcogenides (TMDCs) are promising materials for next-generation optoelectronic devices, owing to their strong excitonic responses and atomic thickness. Controlling their light emission electrically is a crucial step towards realizing practical nanoscale optoelectronic devices such as light-emitting diodes and optical modulators. However, photoluminescence (PL) quenching in van der Waals TMDC/metal heterostructures, caused by ultrafast interlayer charge or energy transfer, impedes such electrical modulation. Here, we investigate monolayer-MoSe2/bulk-NbSe2 heterostructures and demonstrate that a vertical electric field can effectively recover the PL intensity up to ~ 80% of bare-MoSe2. Furthermore, our analysis reveals that the room temperature PL intensity can be tuned by nearly three orders of magnitude in bare-MoSe2 and by about one order of magnitude in MoSe2/NbSe2 heterostructures. First-principles calculations incorporating spin-orbit coupling reveal that the perpendicular electric fields drive a transition from a direct to an indirect bandgap, fundamentally altering the optical response in the heterostructure. Unlike bare-MoSe2, the heterostructure exhibits a pronounced thermal dependence of the enhancement factor, implying that exciton lifetime dominates over interfacial transfer processes. Our findings demonstrate reversible, electric-field-driven PL control at a TMDC/metal interface, providing a pathway to electrically tunable light emission and improved contact engineering in two-dimensional optoelectronic devices.

physics.app-ph↗

arXiv2025

Observation of Kardar-Parisi-Zhang universal scaling in two dimensions

Equilibrium and nonequilibrium states of matter can exhibit fundamentally different behavior. A key example is the Kardar-Parisi-Zhang universality class in two spatial dimensions (2D KPZ), where microscopic deviations from equilibrium give rise to macroscopic scaling laws without equilibrium counterparts. While extensively studied theoretically, direct experimental evidence of 2D KPZ scaling has remained limited to interface growth so far. Here, we report the observation of universal scaling consistent with the KPZ universality class in 2D exciton-polariton condensates -- quantum fluids of light that are inherently driven and dissipative, thus breaking equilibrium conditions. Using momentum-resolved photoluminescence spectroscopy as well as space- and time-resolved interferometry, we probe the phase correlations across microscopically different systems, varying drive conditions in two distinct lattice geometries. Our analysis reveals correlation dynamics and scaling exponents in excellent agreement with 2D KPZ predictions. These results establish exciton-polariton condensates as a robust experimental platform for exploring 2D nonequilibrium universality quantitatively, and open new avenues for investigating the emergence of coherence in interacting quantum systems far from equilibrium.

quant-ph↗

arXiv2025

Artificial Gauge Fields and Dimensions in a Polariton Hofstadter Ladder

Artificial gauge fields allow uncharged particles to mimic the behavior of charged particles subjected to magnetic fields, providing a powerful platform for exploring topological physics. Neutral particles, like photons, are typically unaffected by real magnetic fields. However, it is possible to introduce artificial gauge fields that control the effective dynamics of these neutral particles. Topological exciton-polariton lasers have attracted considerable interest, in part due to the wide range of tunable system parameters, but often require strong magnetic fields to realise propagating topological edge states. Here we show, that by using an artificial gauge field the topological Hall effect in a micron-scale micropillar chain is experimentally realised, exploiting the circular polarisation of polaritons as an artificial dimension. By careful rotational alignment of elliptical micropillars, we introduce an effective plaquette phase that induces strictly polarisation-dependent edge-state propagation, demonstrating non-reciprocal transport of the polariton pseudospins. Our results demonstrate that the dimensionality limitation of topological interface states as well as requirements for strong external magnetic fields in coupled topological laser arrays can be overcome by utilizing polarisation effects and careful engineering of the potential landscape. Our results open new ways towards the implementation of topological polariton lattices and related optically active devices with additional artificial dimension.

physics.optics↗

arXiv2025

Hybrid confinement techniques for polariton simulators

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.

physics.optics↗

arXiv2025

Two-Photon Interference from an InAs Quantum Dot emitting in the Telecom C-Band

Two-photon interference from an InAs/InAlGaAs quantum dot (QD) emitting in the telecom C-band with a raw two-photon interference visibility of $V_{HOM}=(71.9\pm0.2)$ % is demonstrated. This is achieved by a two-fold approach: an improvement of the molecular beam epitaxial growth for better QDs, and integration of the QDs into an optical circular Bragg grating resonator for a Purcell enhancement of the radiative decay rate. The quantum optical properties of the fabricated device are studied by means of time-correlated single-photon counting under quasi-resonant excitation of the charged exciton line. A reduced lifetime of $T_1=(257.5\pm0.2)$ ps is found corresponding to a Purcell factor of $F_P\geqq(4.7\pm0.5)$. Pronounced anti-bunching of the second-order autocorrelation function at zero time delay $g^{(2)} (0)=(0.0307\pm0.0004)$ confirms the single-photon emission character. The two-photon interference is demonstrated with an unbalanced Mach-Zehnder interferometer in Hong-Ou-Mandel configuration. We discuss strategies how to further improve the indistinguishability, and provide a survey of the state-of-the art.

quant-ph↗

arXiv2024

Individually Addressable Nanoscale OLEDs

Augmented Reality (AR) and Virtual Reality (VR), require miniaturized displays with ultrahigh pixel densities. Here, we demonstrate an individually addressable subwavelength OLED pixel based on a nanoscale electrode capable of supporting plasmonic modes. Our approach is based on the notion that when scaling down pixel size, the 2D planar geometry of conventional organic light-emitting diodes (OLEDs) evolves into a significantly more complex 3D geometry governed by sharp nanoelectrode contours. These cause (i) spatially imbalanced charge carrier transport and recombination, resulting in a low quantum efficiency, and (ii) filament growth, leading to rapid device failure. Here, we circumvent such effects by selectively covering sharp electrode contours with an insulating layer, while utilizing a nano-aperture in flat areas of the electrode. We thereby ensure controlled charge carrier injection and recombination at the nanoscale and suppress filament growth. As a proof of principle, we first demonstrate stable and efficient hole injection from Au nanoelectrodes in hole-only devices with above 90 % pixel yield and longtime operation stability and then a complete vertical OLED pixel with an individually addressable nanoelectrode (300 x 300 nm$^{2}$), highlighting the potential to further leverage plasmonic nanoantenna effects to enhance the performance and functionality of nano-OLEDs.

physics.optics↗

arXiv2024

Topological Optical Waveguiding of Exciton-Polariton Condensates

One-dimensional models with topological non-trivial band structures are a simple and effective way to study novel and exciting concepts in topological photonics. In this work we are studying the propagation of light-matter quasi-particles, so called exciton-polaritons, in waveguide arrays. Specifically, we are investigating topological states at the interface between dimer chains, characterized by a non-zero winding number. In order to exercise precise control over the polariton propagation, we study non-resonant laser excitation as well as resonant excitation in transmission geometry. The results highlight a new platform for the study of quantum fluids of light and non-linear optical propagation effects in coupled semiconductor waveguides.

physics.optics↗

arXiv2024

An electrically pumped topological polariton laser

With a seminal work of Raghu and Haldane in 2008, concepts of topology have been successfully introduced in a wide range of optical systems, emulating specific lattice Hamiltonians. Certainly, one of the most promising routes to an application of topological photonics in an actual device are topological lasers, where efficient and highly coherent lasing from a topologically non-trivial mode is achieved. While some attempts have been made to excite such structures electrically, the majority of published fundamental experiments use a form of laser excitation. In this paper, we use a lattice of vertical resonator polariton micropillars to form an exponentially localized topological Su-Schrieffer-Heeger defect. Upon electrical excitation of the p-i-n doped structure, the system unequivocally shows polariton lasing from the topological defect using a carefully placed gold contact. Despite the presence of doping and electrical contacts, the polariton band structure clearly preserves its topological properties. At high excitation power the Mott density is exceeded leading to highly efficient lasing in the weak coupling regime. This work is an important step towards applied topological lasers using vertical resonator microcavity structures.

physics.optics↗