arXiv subjects

Helgi Sigurðsson

Publications and source records attributed to Helgi Sigurðsson.

At least 19 recordsLinked to original sources

arXiv2026

Geometric control of hyperbolic exciton-polariton condensate dimers

Coupled many-body quantum systems exhibit rich emergent physics with diverse stationary and dynamical behaviors. By engineering platforms with tunable and distinct coupling mechanisms, new insights emerge into the collective behavior of coupled many body systems. Particles can be exchanged via evanescent or ballistic coupling: the former, based on proximity, yields large spectral splitting, while the latter requires strict phase-matching, analogous to phase-coupled harmonic oscillators, and has a smaller impact on the energy landscape. We demonstrate an all-optically tunable quantum fluid dimer based on exciton-polariton condensates in a photonic crystal waveguide with hyperbolic (saddle-like) dispersion. Varying the dimer's angle relative to the grating tunes the coupling from evanescent to ballistic. We directly observe spectral features and mass flow shaped by the saddle dispersion. This work highlights photonic crystals as powerful platforms to explore condensed matter phenomena lying at the interface between delay-coupled nonlinear oscillators and tight binding physics.

physics.optics↗

arXiv2026

Discrete chiral ballistic polariton laser

Orbital angular momentum (OAM) of light appears when the phase of an electromagnetic wavefront winds around its direction of propagation, also known as optical vorticity. Contrary to the binary-valued photon spin, the integer-valued optical vortex charge is unbounded with many advantages in optical communication and trapping and enhancing the capacity of data encoding and multiplexing. Singular optoelectronic and chiroptic quantum technologies rely on the development of coherent and compact light sources of well-defined and reconfigurable OAM. We propose an optically tunable discrete chiral exciton-polariton microlaser that leverages strong spin-dependent polariton interactions, structured pumping, and inherent cavity photon spin-to-angular momentum conversion to emit coherent nonlinear light of variable OAM. By choosing pumping patterns with broken inversion symmetry in the microcavity plane we invoke geometric frustration between spinor ballistic condensates which spontaneously obtain a high-charge circulating current locked with the pump polarization. Our optically configurable system requires only a planar cavity thus avoiding the need for specialized irreversible cavity patterning or metasurfaces.

cond-mat.mes-hall↗

arXiv2026

Critical states and anomalous wave transport in an aperiodic polariton monotile

Recently "the Hat" monotile was introduced into the family of aperiodic tilings and quasicrystals boasting physical properties lying at the boundary of ordered and disordered systems. Here we study the two-dimensional wave transport, transverse localization and scaling properties of the quantum modes in a Monotile quasilattice. Our system is based on reconfigurable optical lattices for cavity-polaritons which provide flexible means to study wavepacket dynamics, strong nonlinear phenomena, and power-driven condensation in this new type of an aperiodic tiling. We confirm the existence of localized and critical states in the Monotile through direct diagonalization of the Schrödinger equation. Scaling analysis on the moments of the wavefunction distribution reveals anomalous transport regimes of super-diffusive and near sub-diffusive polariton transport associated with the fractal structure of the Monotile Hilbert space. We propose a strategy using resonantly excited polariton fluids to verify our findings.

cond-mat.mes-hall↗

arXiv2026

Electrically reconfigurable extended lasing state in an organic liquid-crystal microcavity

Small-footprint, low-power arrays of coupled coherent emitters with the capability of near- and far-field engineering and coherence control are highly sought after to meet modern nanophotonics evolving needs. Between existing solutions based on vertical-cavity surface-emitting lasers, phase masks in bulk traditional cavity-based systems, and lattices of exciton-polariton condensates, only the strongly light-matter coupled systems were shown to be capable of controlled on-chip interaction between the individual coherent states while often operating at cryogenic temperatures. Here we demonstrate electrically controlled in-plane interaction between optically reconfigurable spatially separated lasing states, operating at room temperature in the weak light-matter coupling regime. We show spatially extended coherent lasing state or "supermode" with wide-range micro-scale control of near-field, far-field and on-chip phase-locking tuning functionality. An extended lasing state appears due to near-field transverse coupling between distinct spatially pumped lasing states in the plane of an organic liquid crystal-filled microcavity. We realize electrical control over the interaction strength between lasing states and corresponding mutual coherence going beyond nearest neighbours through electrical tuning of the microcavity optical modes with external voltage, and a spin-selective directional coupling regime by using a photonic analogue of the Rashba-Dresselhaus spin-orbit interaction.

cond-mat.mes-hall↗

arXiv2026

Optically trapped exciton-polariton condensates in a perovskite microcavity

We demonstrate room temperature optical trapping and generation of high-order angular harmonics in exciton-polariton condensates in a monocrystalline CsPbBr$_3$ perovskite-filled microcavity. Using an annular nonresonant excitation profile focused onto the perovskite, we observed power-driven switching between different transverse modes of the optically induced trap. We explore the interplay between the perovskite crystal dimensions and the optical trap diameter that allows the condensate to transition from whispering gallery-like petal shapes to extended ripple states. Our results underline the feasibility in creating high-order quantum states in perovskite polariton condensates for reconfigurable and structured room temperature nonlinear lasing.

physics.optics↗

arXiv2025

Chiral polariton transport enabled by optical spin Hall effect in perovskite waveguides

Controlling the spin degree of freedom of light at the microscale is crucial for advancing photonic information processing. Spin polarized light propagation, combined with strong optical nonlinearities, unlocks new functionalities in compact photonic circuits and active spin optronic devices. Lead halide perovskite exciton polaritons uniquely combine room temperature operation, pronounced nonlinearities, and versatile microstructuring, making them a powerful platform for spin based photonic technologies. Here, we demonstrate polarized edge emission from polariton condensates in perovskite single crystals predesigned into a microwire, forming natural, DBR free cavity. Above threshold, we observe a distinct waveguiding optical spin Hall effect pattern in both real- and reciprocal-space emission, accompanied by pseudospin phase locking arising from coherence between opposite edges. Beyond static polarization textures, we achieve spin-resolved polariton edge lasing with chirality exceeding 80\% and spin-polarized signal propagation over tens of micrometres. These results establish CsPbBr3 waveguides as a promising easy to fabricate platform for on chip spin coded information transport and nonlinear spin optoelectronics.

cond-mat.other↗

arXiv2025

Observation of σ-πcoupling and mode selection in optically trapped artificial polariton molecules

Microcavity exciton-polariton condensates under additional transverse confinement constitute a flexible optical platform to study the coupling mechanism between confined nonequilibrium and nonlinear states of matter. Driven far from equilibrium, polariton condensates can display spontaneous synchronization and instabilities depending on excitation and material parameters, showcasing emergent and intricate interference patterns based on mode competition over mutual gain landscapes. Here, we explore this coupling mechanism between polariton condensates populating the first excited ${\it p}$-state manifold of coupled optically trapped condensates and show a rich structure of patterns based on excitation parameters. The optical reconfigurability of the laser excitation patterns enables the creation of an annular-shaped beam to confine polaritons in a tailored trapping potential, whilst the dissipative nature of the optical traps enables effective interaction with neighboring condensates. Our results underpin the potential role of polariton condensates in exploring and simulating $σ$ and $π$ molecular bonding mechanisms between artificial two-dimensional diatomic orbitals and beyond.

cond-mat.mes-hall↗

arXiv2025

Breakdown of Bulk-Radiation Correspondence in Radiative Photonic Lattices

The topological characteristics of energy bands in crystalline systems are encapsulated in the Berry curvature of the bulk Bloch states. In photonic crystal slabs, far-field emission from guided resonances naturally provides a non-invasive way to probe the embedded wavefunctions, raising the question of how the information carried by escaping photons relates to the band topology. We develop a non-Hermitian model to describe the guided and leaky modes of photonic crystal slabs with long-range couplings and non-local responses. Within this framework, radiation Berry curvature is defined from the far-field polarization and compared to the conventional bulk Berry curvature of the crystal Bloch modes. We investigate this bulk-radiation correspondence in the vicinity of the $Γ$-point of the square lattice and the $K$-point of the honeycomb lattice. The results show that the comparability between the bulk topology and the radiation topology is not universal; the validity is contingent upon the specific bulk Bloch states. Notably, the correspondence completely breaks down surrounding the far-field singularities, while it can hold in smooth regions under special symmetry conditions, e.g., rotational symmetry. Besides, net Berry curvature concentration is captured at the valleys of the non-local honeycomb lattice, facilitating further exploration on generalized topological phases in photonic lattices beyond the regimes with localized couplings and Hermiticity.

physics.optics↗

arXiv2025

Topological Jackiw-Rebbi States in Photonic Van der Waals Heterostructures

Topological phenomena, first studied in solid state physics, have seen increased interest for applications in nanophotonics owing to highly controllable light confinement with inherent robustness to defects. Photonic crystals can be designed to host topologically protected interface states for directional light transport, localization and robust lasing via tuning of the bulk topological invariant. At the same time, van der Waals (vdW) materials, in both their monolayer and quasi-bulk forms, are emerging as exciting additions to the field of nanophotonics, with a range of unique optoelectronic properties and intrinsic adherence to any type of host material, allowing fabrication of complex multi-layer structures. We present here a 1D topological photonic platform made from stacked nanostructured and planar layers of quasi-bulk WS$_2$ to achieve Jackiw-Rebbi (JR) interface states between two topologically distinct gratings in the near-infrared range around 750 nm. Such states are measured in the far-field with angle-resolved reflectance contrast measurements, exhibiting linewidth of 10 meV and highly directional emission with an angular bandwidth of 8.0$^\circ$. Subsequent local mapping of the structure via sub-wavelength resolution scattering-type scanning near-field optical microscopy (s-SNOM) reveals strong spatial confinement of the JR state to the grating interface region. Finally, we couple in the JR state the photoluminescence of monolayer WSe$_2$ incorporated in a five-layer vdW grating heterostructure, giving rise to directional enhancement of the excitonic emission of up to 22 times that of uncoupled monolayer, thus demonstrating the potential of the topological interface states for highly directional light emission in addition to light scattering.

physics.optics↗

arXiv2025

Electrically tunable momentum space polarization singularities in liquid crystal microcavities

Momentum space polarization singularities of light appear as vectorial twists in the scattered and radiated far field patterns of exotic photonic structures. They relate to important concepts such as bound states in the continuum, spatiotemporal light steering, polarization Möbius strips, Berry curvature and associated topological photonic phenomena. Polarization singularities, such as completely circularly polarized C-points, are readily designed in real space through interference of differently polarized beams. In momentum space, they require instead sophisticated patterning of photonic crystal slabs of reduced symmetries in order to appear in the corresponding band structure with scarce in-situ tunability. Here, we show that momentum space singularities can be generated and, importantly, electrically tuned in the band structure of a highly birefringent planar liquid crystal microcavity that retains many symmetries. Our results agree with theoretical predictions and offer exciting possibilities for integration of momentum space polarization singularities in spinoptronic technologies.

physics.optics↗

arXiv2024

Quantum Fluids of Light in 2D Artificial Reconfigurable Aperiodic Crystals with Tailored Coupling

Aperiodic crystals are the intermediates between strictly periodic crystalline matter and amorphous solids. The lack of translational symmetry combined with intrinsic long-range order endows aperiodic crystals with unique physical characteristics, while at the same time dramatically enriching the spectrum and localization properties. Here, we demonstrate exciton-polariton condensation in a two-dimensional Penrose tiling with $C_{10}$ rotational symmetry - the first signature of quasicrystalline order in a quantum fluid of light. We identify a regime, wherein near-perfect delocalization and synchronization of a quantum fluid of light occurs at mesoscopic length-scales extending beyond 100x the healing length and the size of each individual condensate. Realizing long-range order in fully reconfigurable aperiodic crystals of nonlinear, and open-dissipative quantum fluids, lays the foundations for testing a broad range of universality classes of continuous phase transitions beyond the limits of mathematically verifiable models in regular lattices.

cond-mat.quant-gas↗

arXiv2024

Antiferromagnetic Ising model in a triangular vortex lattice of quantum fluids of light

Vortices are topologically distinctive objects appearing as phase twists in coherent fields of optical beams and Bose-Einstein condensates. Structured networks and artificial lattices of coupled vortices could offer a powerful platform to study and simulate interaction mechanisms between constituents of condensed matter systems, such as antiferromagnetic interactions, by replacement of spin angular momentum with orbital angular momentum. Here, we realize such a platform using a macroscopic quantum fluid of light based on exciton-polariton condensates. We imprint all-optical hexagonal lattice that results into a triangular vortex lattice, with each cell having a vortex of charge l = +-1. We reveal that pairs of coupled condensates spontaneously arrange their orbital angular momentum antiparallel, implying a form of artificial orbital "antiferromagnetism". We discover that correlation exists between the emergent vortex patterns in triangular condensate lattices and the low-energy solutions of the corresponding antiferromagnetic Ising system. Our study offers a path toward spontaneously ordered vortex arrays with nearly arbitrary configurations and controlled couplings.

cond-mat.mes-hall↗

arXiv2024

Non-Hermitian polariton-photon coupling in a perovskite open microcavity

Exploring the non-Hermitian properties of semiconductor materials for optical applications is at the forefront of photonic research. However, the selection of appropriate systems to implement such photonic devices remains a topic of debate. In this work, we demonstrate that a perovskite crystal, characterized by its easy and low-cost manufacturing, when placed between two distributed Bragg reflectors with an air gap, can form a natural double microcavity. This construction shows promising properties for the realisation of novel, tunable non-Hermitian photonic devices through strong light-matter coupling. We reveal that such a system exhibits double-coupled polariton modes with dispersion including multiple inflection points. Owing to its non-Hermiticity, our system exhibits nonreciprocal properties and allows for the observation of exceptional points. Our experimental studies are in agreement with the theoretical analysis based on coupled mode theory and calculations based on transfer matrix method.

cond-mat.mes-hall↗

arXiv2024

Occupancy-driven Zeeman suppression and inversion in trapped polariton condensates

We study the magneto-photoluminescence of an optically trapped exciton-polariton condensate in a planar semiconductor microcavity with multiple In0.08Ga0.92As quantum wells. Extremely high condensate coherence time and continuous control over the polariton confinement are among the advantages provided by optical trapping. This allows us to resolve magnetically induced μeV fine-energy shifts in the condensate and identify unusual dynamical regions in its parameter space. We observe polariton Zeeman splitting and, in small traps with tight confinement, demonstrate its full parametric screening when the condensate density exceeds a critical value, reminiscent of the spin-Meissner effect. For larger optical traps, we observe a complete inversion in the Zeeman splitting as a function of power, underlining the importance of condensate confinement and interactions with its background reservoir excitons.

cond-mat.mes-hall↗

arXiv2024

Magneto-optical induced supermode switching in quantum fluids of light

The insensitivity of photons towards external magnetic fields forms one of the hardest barriers against efficient magneto-optical control, aiming at modulating the polarization state of light. However, there is even scarcer evidence of magneto-optical effects that can spatially modulate light. Here, we demonstrate the latter by exploiting strongly coupled states of semimagnetic matter and light in planar semiconductor microcavities. We nonresonantly excite two spatially adjacent exciton-polariton condensates which, through inherent ballistic near field coupling mechanism, spontaneously synchronise into a dissipative quantum fluidic supermode of definite parity. Applying a magnetic field along the optical axis, we continuously adjust the light-matter composition of the condensate exciton-polaritons, inducing a supermode switch into a higher order mode of opposite parity. Our findings set the ground towards magnetic spatial modulation of nonlinear light.

cond-mat.mes-hall↗

arXiv2024

Dirac exciton-polariton condensates in photonic crystal gratings

Bound states in the continuum have recently been utilized in photonic crystal gratings to achieve strong coupling and ultralow power-driven condensation of bosonic exciton-polariton quasiparticles with atypical Dirac-like features in their dispersion relation. Here, we develop the single- and many-body theory of these new effective relativistic exciton-polaritons modes and describe their mean field condensation dynamics facilitated by the interplay between protection from the radiative continuum and negative-mass pump induced optical trapping. Our theory accounts for many tunable grating parameters giving full control over the diffractive coupling properties between guided polaritons and the radiative continuum previously unexplored in the context of driven condensation. In particular, we discover stable cyclical condensate solutions mimicking a driven-dissipative analog of the zitterbewegung effect characterized by coherent superposition of both ballistic (rapid phase front) and trapped (slow phase front) polariton waves. Finally, important distinctions are drawn between the concepts of near field and far field in the photonic grating, clarifying recent experimental observations on the emission characteristics of these long lived nonlinear Dirac polaritons.

cond-mat.mes-hall↗

arXiv2023

Directional planar antennae in polariton condensates

We report on the realization of all-optical planar microlensing for exciton-polariton condensates in semiconductor microcavities. We utilize spatial light modulators to structure a nonresonant pumping beam into a planoconcave lens-shape focused onto the microcavity plane. When pumped above condensation threshold, the system effectively becomes a directional polariton antenna, generating an intense focused beam of coherent polaritons away from the pump region. The effects of pump intensity, which regulates the interplay between gain and blueshift of polaritons, as well as the geometry of lens-shaped pump are studied and a strategy to optimize the focusing of the condensate is proposed. Our work underpins the feasibility to guide nonlinear light in microcavities using nonresonant excitation schemes, offering perspectives on optically reprogrammable on-chip polariton circuitry.

cond-mat.mes-hall↗

arXiv2023

Optically driven spin precession in polariton condensates

External driving of spinor degrees of freedom by magnetic or optical fields in quantum systems underpin many applications ranging from nuclear magnetic resonance to coherent state control in quantum computing. Although spinor polariton condensates are offering a flexible platform for spinoptronic applications, strong inter-particle interactions limit their spin coherence. Here, we introduce an all-optically driven spin precession in microcavity polariton condensates that eliminates depolarisation, through a radio frequency modulation of a spatially rotating, asymmetric exciton reservoir that both confines, and actively replenishes the polariton condensate. We realise several GHz driven spin precession with a macroscopic spin coherence time that is limited only by the extraneous to the condensate, frequency drift of the composite pumping sources. Our observations are supported by mean field modelling and evidence a driven-dissipative quantum fluidic analogue of the nuclear magnetic resonance effect.

physics.optics↗