arXiv subjects

Darius Urbonas

Publications and source records attributed to Darius Urbonas.

16 recordsLinked to original sources

arXiv2026

Stimulated cooling in non-equilibrium Bose-Einstein condensate

We report on the experimental observation of stimulated cooling in the non-equilibrium Bose-Einstein condensate (BEC) of weakly interacting exciton-polaritons from approximately room temperature down to 20K. By resolving the condensate in energy-momentum space and performing interferometric measurements, we distinguish the condensate from thermalized particles yet occupying excited states macroscopically. In contrast to the analytical quantum theories of non-equilibrium BEC [Shishkov et al., Phys. Rev. Lett. 128, 065301 (2022)], we observe segmentation of the particle density along the excited states into two fractions both following Bose-Einstein distribution, albeit with different effective temperatures and chemical potentials. Our results indicate that the temperature of the weakly interacting Bose gas is universally set by the density-dependent chemical potential, revealing a defining property of non-equilibrium BECs. Finally, we demonstrate that the stimulated nature of the cooling process directly governs the emergence of quantum coherence of the condensate and shapes the dissipative properties of the excited states.

cond-mat.quant-gas↗

arXiv2025

Kibble-Zurek mechanism in a polariton supersolid

We study the formation of topological defects via the Kibble-Zurek mechanism in a polariton supersolid in a liquid crystal microcavity with tunable Rashba-Dresselhaus spin-orbit coupling. We predict analytically two different scalings in the slow- and fast-quench regimes, and confirm these predictions numerically. We also present experimental results for the slow-quench regime, demonstrating an original Kibble-Zurek scaling exponent $η_{KZM}=1.0\pm 0.2$

cond-mat.mes-hall↗

arXiv2025

Observation of a supersolid phase in a spin-orbit coupled exciton-polariton Bose-Einstein condensate at room temperature

In Bose-Einstein condensates (BEC), spin-orbit coupling (SOC) produces supersolidity. It is a peculiar state of matter, which, in addition to the superfluid behaviour shows periodic density modulation typical for crystals. Here, we report the fabrication of a new type of optical microcavity allowing to achieve room-temperature supersolidity for a quantum fluid of light. The microcavity is filled with a nematic liquid crystal (LC) and two layers of the organic polymer MeLPPP hosting exciton resonances. We demonstrate exciton-polariton condensation in the two distinct degenerate minima of the dispersion created by the LC induced Rashba-Dresselhaus (RD) SOC. The condensate real-space distribution shows density stripes located randomly from one condensate realization to another despite the presence of a random disorder potential. This demonstrates the immunity of stripes against disorder (that is, superfluidity) and the spontaneous breaking of translational invariance. We also report the random appearance of vortices via the Kibble-Zurek mechanism, another smoking gun of superfluidity.

cond-mat.mes-hall↗

arXiv2025

Entangled Polariton States in the Visible and Mid-Infrared Spectral Ranges

Entanglement generation in polariton systems is fundamentally constrained by high losses and decoherence, which typically outweigh polariton nonlinearities. Here, we propose a conceptually different approach that uses optomechanical interactions, rather than polariton-polariton interactions, to generate entangled polaritons. Our double-resonant scheme relies on strong exciton-phonon coupling, found in both inorganic and molecular semiconductors, enabling room-temperature generation of spectrally disparate photon pairs. The quantum coherent and delocalized nature of polariton states inside optical cavities ensures efficient single-mode outcoupling and allows for unconditional quantum state preparation - not relying on any post-selection or projective measurements. When conditioned on exciton-polariton emission, single phonon-polariton states can be prepared that subsequently yield bright, heralded single-photon emission in the mid-IR/THz. We introduce a double-resonant optomechanical platform that enables scalable, room-temperature quantum polaritonics without relying on conventional excitonic nonlinearities.

quant-ph↗

arXiv2025

Purcell-enhanced single-photon generation from CsPbBr$_3$ quantum dots in in-situ selected Laguerre-Gaussian modes

Single photons in Laguerre-Gaussian (LG) beams, which carry orbital angular momentum (OAM), could enable more robust and efficient photonic quantum communication and information processing, as well as enhanced sensitivity in quantum metrology and imaging. However, as most implementations are indirect or require additional mode-shaping elements, direct generation of single photons with OAM has received growing interest. Colloidal lead halide perovskite quantum dots (QDs) have recently emerged as a versatile material that can produce indistinguishable single photons quasi-deterministically at high rate. Here, we integrate single CsPbBr$_3$ QDs into an open Fabry-Perot microcavity with a nanofabricated Gaussian-shaped deformation, demonstrating Purcell-enhanced single-photon generation into individual cavity modes with up to 18.1 $\pm$ 0.2 times accelerated decay, down to tens of picoseconds. By in-situ tuning of the cavity resonance, we can selectively couple a single QD to different LG modes carrying OAM and observe the spatial patterns of the generated single-photon beams emitted from the cavity. Our findings open the door to high photon rate sources that directly generate single-photon LG beams for advanced quantum photonic applications.

physics.optics↗

arXiv2025

Integrated, ultrafast all-optical polariton transistors with sub-wavelength grating microcavities

All-optical logic has the potential to overcome the operation speed barrier that has persisted in electronic circuits for two decades. However, the development of scalable architectures has been prevented so far by the lack of materials with sufficiently strong nonlinear interactions needed to realize compact and efficient ultrafast all-optical switches with optical gain. Microcavities with embedded organic material in the strong light-matter interaction regime have recently enabled all-optical transistors operating at room temperature with picosecond switching times. However, the vertical cavity geometry, which is predominantly used in polaritonics, is not suitable for complex circuits with on-chip coupled transistors. Here, by leveraging state-of-the-art silicon photonics technology, we have achieved exciton-polariton condensation at ambient conditions in fully integrated high-index contrast sub-wavelength grating microcavities filled with a pi-conjugated polymer as optically active material. We demonstrate ultrafast all-optical transistor action by coupling two resonators and utilizing seeded polariton condensation. With a device area as small as 2x2 um^2, we realize picosecond switching and amplification up to 60x, with extinction ratio up to 8:1. This compact ultrafast transistor device with in-plane integration is a key component for a scalable platform for all-optical logic circuits that could operate two orders of magnitude faster than electronic ones.

physics.optics↗

arXiv2024

A framework to compute resonances arising from multiple scattering

Numerous natural and technological phenomena are governed by resonances. In nanophotonics, resonances often result from the interaction of several optical elements. Controlling these resonances is an excellent opportunity to provide light with properties on demand for applications ranging from sensing to quantum technologies. The inverse design of large, distributed resonators, however, is typically challenged by high computational costs when discretizing the entire system in space. Here, this limitation is overcome by harnessing prior knowledge about the individual scatterers that form the resonator and their interaction. In particular, a transition matrix multi-scattering framework is coupled with the state-of-the-art adaptive Antoulas-Anderson (AAA) algorithm to identify complex poles of the optical response function. A sample refinement strategy suitable for accurately locating a large number of poles is introduced. We tie the AAA algorithm into an automatic differentiation framework to efficiently differentiate multi-scattering resonance calculations. The resulting resonance solver allows for efficient gradient-based optimization, demonstrated here by the inverse design of an integrated exciton-polariton cavity. This contribution serves as an important step towards efficient resonance calculations in a variety of multi-scattering scenarios, such as inclusions in stratified media, periodic lattices, and scatterers with arbitrary shapes.

physics.comp-ph↗

arXiv2024

Room-temperature cavity exciton-polariton condensation in perovskite quantum dots

The exploitation of the strong light-matter coupling regime and exciton-polariton condensates has emerged as a compelling approach to introduce strong interactions and nonlinearities into numerous photonic applications, ranging from low-threshold topological lasers to ultrafast all-optical logic devices. The use of colloidal semiconductor quantum dots with strong three-dimensional confinement as the active material in these microcavities would be highly advantageous due to their versatile structural and compositional tunability and wet-chemical processability, as well as potentially enhanced, confinement-induced polaritonic interactions. Yet, to date, cavity exciton-polariton condensation has neither been achieved with epitaxial nor with colloidal quantum dots. Here, we demonstrate room-temperature polariton condensation in a thin film of monodisperse, colloidal CsPbBr$_3$ quantum dots placed in a tunable optical resonator with a Gaussian-shaped deformation serving as wavelength-scale potential well for the polaritons. The onset of polariton condensation under pulsed optical excitation is manifested in emission by its characteristic superlinear intensity dependence, reduced linewidth, blueshift, and extended temporal coherence. Our results, based on this highly engineerable class of perovskite materials with unique optical properties, pave the way for the development of polaritonic devices for ultrabright coherent light sources and photonic information processing.

physics.optics↗

arXiv2024

In-situ tunneling control in photonic potentials by Rashba-Dresselhaus spin-orbit coupling

The tunability of individual coupling amplitudes in photonic lattices is highly desirable for photonic Hamiltonian engineering and for studying topological transitions in situ. In this work, we demonstrate the tunneling control between individual lattice sites patterned inside an optical microcavity. The tuning is achieved by applying a voltage to a liquid crystal microcavity possessing photonic Rashba-Dresselhaus spin-orbit coupling. This type of spin-orbit coupling emerges due to the high birefringence of the liquid crystal material and constitutes an artificial gauge field for photons. The proposed technique can be combined with strong-light matter coupling and non-Hermitian physics already established in liquid crystal microcavities.

physics.optics↗

arXiv2024

Perovskite nanocrystal self-assemblies in 3D hollow templates

Highly ordered nanocrystal (NC) assemblies, namely superlattices (SLs), have been investigated as novel building blocks of optical and optoelectronic devices due to their unique properties based on interactions among neighboring NCs. In particular, lead halide perovskite NC SLs have attracted significant attention, owing to their extraordinary optical characteristics of individual NCs and collective emission processes like superfluorescence (SF). So far, the primary method for preparing perovskite NC SLs has been the drying-mediated self-assembly method, in which the colloidal NCs spontaneously assemble into SLs during solvent evaporation. However, this method lacks controllability because NCs form random-sized SLs at random positions on the substrate rendering NC assemblies in conjunction with device structures such as photonic waveguides or microcavities challenging. Here, we demonstrate template-assisted self-assembly to deterministically place perovskite NC SLs and control their geometrical properties. A solution of CsPbBr3 NCs is drop-casted on a substrate with lithographically-defined hollow structures. After solvent evaporation and removal of excess NCs from the substrate surface, NCs only remain in the templates thereby defining the position and size of these NC assemblies. We performed photoluminescence (PL) measurements on these NC assemblies and observed signatures of SF, similar as in spontaneously assembled SLs. Our findings are crucial for optical devices that harness embedded perovskite NC assemblies and prepare fundamental studies on how these collective effects can be tailored through the SL geometry.

cond-mat.soft↗

arXiv2024

In-situ tunable, room-temperature polariton condensation in individual states of a 1D topological lattice

In recent years, exciton-polariton microcavity arrays have emerged as a promising semiconductor-based platform for analogue simulations of model Hamiltonians and topological effects. To realize experimentally a variety of Hamiltonians and change their parameters, it is essential to have highly tunable and easily engineerable structures. Here, we demonstrate in-situ tunable, room-temperature polariton condensation in individual states of a one-dimensional topological lattice, by utilizing an open-cavity configuration with an organic polymer layer. Angle-resolved photoluminescence measurements reveal the band structure of the Su-Schrieffer-Heeger chain, comprised of S-like and P-like bands, along with the appearance of discrete topological edge states with distinct symmetries. Changing the cavity length in combination with vibron-mediated relaxation in the polymer allows us to achieve selective polariton condensation into different states of the band structure, unveiled by nonlinear emission, linewidth narrowing, energy blue-shift and extended macroscopic coherence. Furthermore, we engineer the bandgap and the edge state localization by adjusting the interaction between adjacent lattice sites. Comparison to first-principles calculations showcases the precision of the polariton simulator. These results demonstrate the versatility and accuracy of the platform for the investigation of quantum fluids in complex potential landscapes and topological effects at room temperature.

cond-mat.mes-hall↗

arXiv2021

Organic single-photon switch

The recent progress in nanotechnology [1,2] and single-molecule spectroscopy [3-5] paves the way for cost-effective organic quantum optical technologies emergent with a promise to real-life devices operating at ambient conditions. In this letter, we harness $π$-conjugated segments of an organic ladder-type polymer strongly coupled to a microcavity forming correlated collective dressed states of light, so-called of exciton-polariton condensates. We explore an efficient way for all-optical ultra-fast control over the macroscopic condensate wavefunction via a single photon. Obeying Bose statistics, exciton-polaritons exhibit an extreme nonlinearity undergoing bosonic stimulation [6] which we have managed to trigger at the single-photon level. Relying on the nature of organic matter to sustain stable excitons dressed with high energy molecular vibrations we have developed a principle that allows for single-photon nonlinearity operation at ambient conditions opening the door for practical implementations like sub-picosecond switching, amplification and all-optical logic at the fundamental limit of single light quanta.

cond-mat.mes-hall↗

arXiv2020

All-optical cascadable universal logic gate with sub-picosecond operation

Today, almost all information processing is performed using electronic logic circuits operating with up to several gigahertz frequency. All-optical logic, however, that holds the promise to allow up to three orders of magnitude higher speed [1] has not been able to provide a viable alternative because approaches that had been tried were either not scalable, not energy efficient or did not show a significant speed benefit. Whereas essential all-optical transistor functionalities have been already demonstrated across a range of platforms [2-4], using them to implement the complete Boolean logic gate set and in particular negation - switching off an optical signal with another optical signal - poses a major challenge [5]. Here, we realize a universal NOR logic gate by introducing the concept of non-ground-state dynamic exciton-polariton condensation in an organic semiconductor microcavity under non-resonant pulsed excitation. In the presence of either of the input signals inserted at opposite in-plane momenta, non-ground state dynamic condensation supersedes spontaneous ground-state condensation, resulting in a NOR-operator output signal within less than a picosecond. An additional optical transistor, fed by the output of the NOR gate, is then used to regenerate the output signal such that it is usable as input for cascading gates, a prerequisite for scale up. Our results constitute an essential step towards the realization of more complex logic optical circuitry that could boost future information processing applications.

physics.optics↗

arXiv2019

Molecular structure elucidation with charge-state control

The charge state of a molecule governs its physicochemical properties, such as conformation, reactivity and aromaticity, with implications for on-surface synthesis, catalysis, photo conversion and applications in molecular electronics. On insulating, multilayer NaCl films we control the charge state of organic molecules and resolve their structures in neutral, cationic, anionic and dianionic states by atomic force microscopy, obtaining atomic resolution and bond-order discrimination using CO functionalized tips. We detect changes in conformation, adsorption geometry and bond-order relations for azobenzene, tetracyanoquinodimethane and pentacene in multiple charge states. Moreover, for porphine we investigate the charge-state-dependent change of aromaticity and conjugation pathway in the macrocycle. This work opens the way to studying chemical-structural changes of individual molecules for a wide range of charge states.

cond-mat.mes-hall↗

arXiv2019

Zero-dimensional organic exciton-polaritons in tunable coupled Gaussian defect microcavities at room temperature

We demonstrate strong light-matter interaction at ambient conditions between a ladder-type conjugated polymer and the individual modes of a vertical microcavity with tunable resonance frequencies. Zero-dimensional wavelength-scale confinement for the polaritons is achieved through a sub-micron sized Gaussian defect, resulting in a vacuum Rabi splitting of the polariton branches of 2g = 166 meV. By placing a second Gaussian defect nearby, we create a polaritonic molecule with tunnel coupling strength of up to 2J ~ 50 meV. This platform enables the creation of tailor-made potential landscapes with wavelength-scale dimensions and tunable coupling strengths beyond the thermal energy, opening a route towards room-temperature polariton-based quantum simulators.

cond-mat.mes-hall↗

arXiv2019

Room-Temperature Exciton-Polariton Condensation in a Tunable Zero-Dimensional Microcavity

We create exciton-polaritons in a zero-dimensional (0D) microcavity filled with organic ladder-type conjugated polymer in the strong light-matter interaction regime. Photonic confinement at wavelength scale is realized in the longitudinal direction by two dielectric Bragg mirrors and laterally by a sub-micron Gaussian-shaped defect. The cavity is separated into two parts allowing nanometer position control and enabling tuning of exciton and photon fractions of the polariton wavefunction. Polariton condensation is achieved with non-resonant, picosecond optical excitation at ambient conditions and evidenced by a threshold behavior with non-linear increase of the emission intensity, line narrowing and blue-shift of the emission peak. Furthermore, angular emission spectra show that condensation occurs in the ground state of the 0D-cavity, and first order coherence measurements reveal the coherent nature. These experiments open the door for polariton quantum fluids in complex external potentials at room temperature.

cond-mat.mes-hall↗