Conference Agenda

Ultra-confined Light and Ultra-Strong Coupling Regime with phonon polaritions

Microscale coherent light sources are fundamental to photonic technologies, enabling applications in metrology, data processing, and high-speed computation. Photonic chips that integrate both gain and passive sections are poised to revolutionize optical communications by reducing system complexity and supporting logic operations at higher bandwidths and spped. Organic materials offer a compelling platform for these applications due to their rich optical transitions, mechanical flexibility, and chemical compatibility, making them ideal candidates for multifunctional soft photonics.

In this work, we investigate light-harvesting supramolecular complexes, characterized by strong absorption and extensive exciton delocalization, as antenna systems coupled with acceptor dyes to enhance light–matter interaction within optical microcavities.

Dye aggregates embedded in polymer matrices, confined between metal mirrors to form optical microcavities, exhibit clear polariton signatures characterized by large Rabi splitting energies, as demonstrated by angular-resolved transmittance and fluorescence measurements. This study demonstrates the potential of organic microcavities for advanced optoelectronic applications, particularly in enhancing energy transfer between distinct molecular species. Ongoing research aims to extend these findings through the integration of biological and nanostructured materials, broadening the scope of organic polaritonics and hybrid light-harvesting technologies.

Magnons and plasmons are different collective modes, involving the spin and charge degrees of freedom, respectively. Formation of hybrid plasmon–magnon polaritons in heterostructures of plasmonic and magnetic systems faces two challenges, the small interaction of the electromagnetic field of the plasmon with the spins, and the energy mismatch, as in most systems plasmons have energies orders of magnitude larger than those of magnons. We show that graphene plasmons form polaritons with the magnons of two-dimensional ferromagnetic insulators, placed up to to half a micrometer apart, with Rabi splittings in the range of 100 GHz (dramatically larger than cavity magnonics). This is facilitated both by the small energy of graphene plasmons and the cooperative super-radiant nature of the plasmon–magnon coupling afforded by phase matching. We show that the coupling can be modulated both electrically and mechanically, and we propose a ferromagnetic resonance experiment implemented with a two-dimensional ferromagnet driven by graphene plasmons.

Composite electronic excitations such as polarons and excitons, play a crucial role in the optical response of quantum materials. However, the complex underlying physics of their quasiparticles, and in particular excitons often makes it challenging to measure or infer key excitonic parameters directly from experiments. In recent years, Hamiltonian learning is an emerging approach in physics that combines theoretical modeling with machine learning algorithms to extract physical parameters from experimental data. Here, we investigate the use of Hamiltonian learning to infer excitonic parameters in one-dimensional systems. We perform exact many-body simulations of interacting models featuring excitons, demonstrating their real-time dynamics. The results will be used for training machine learning models to learn the mapping between observable quantities and underlying physical parameters. Once trained, these models will be used to infer excitonic parameters in more general systems. Ultimately, this strategy can be extended to capture more complex optical excitations phenomena, including doublons, trions, and biexcitons. This work will pave way to perform Hamiltonian learning from the dynamics of composite electronic excitations, combining quantum many-body methods, machine learning and experimental observables in quantum materials.

Chirality-driven spin configurations hold great potential for advancing spintronics by enabling compact, energy-efficient memory devices and high-density data storage solutions. Here, we will present our experimental results of spin structures in 2D van der Waals magnet. These spin configurations exhibit distinct optical characteristics, arising from spin interactions influenced by external magnetic fields and thermal variations. The observed chiral optical responses serve as a highly sensitive probe for detecting non-collinear spin arrangements. Our findings highlight 2D magnetic materials and their heterostructures as promising candidates for reconfigurable spin-photonics and spintronic applications.

Optical metasurfaces have emerged as powerful, flat photonic elements capable of tailoring light at the sub-wavelength scale. In particular, quasi-bound states in the continuum (qBIC) metasurfaces enable the creation of high quality (Q) factor resonances in ultrathin nanophotonic structures, offering a promising route to enhanced light–matter interactions. In this talk, I will present our recent advances in integrating van der Waals (vdW) materials with qBIC metasurfaces to realize robust exciton–polaritons. We first demonstrate self-hybridized polaritons in patterned WS2 metasurfaces, where the interplay between excitons and engineered photonic modes leads to Rabi splitting above 100 meV, in ambient conditions. Furthermore, we explore hBN-based dielectric metasurfaces supporting ultra-high Q resonances, with values exceeding 2000 across the visible range. Finally, by vertically stacking hBN with WS2 monolayer semiconductors, we realize room-temperature exciton-polaritons in vdW heterostructures, with nonlinearities three orders of magnitude larger than previous approaches. Our results pave the way for compact polaritonic devices with enhanced nonlinear responses, offering new avenues for low-threshold condensation and coherent photonic circuits operating at room temperature.

We present a hydrodynamic model based on Madelung's approach to describe the plasmonic properties of anisotropic materials. In this modelling, nonlocal effects arise from the Bohm potential and Thomas-Fermi quantum pressure.

We find exact formulas for the dispersion relation of magnetoplasmons and the optical conductivity, considering nonlocal effects. We apply them to monolayer phosphorene, a two-dimensional material known for its anisotropic properties. The plasmon dispersion of our model matches well with results from first-principles calculations.

Our findings show that including nonlocal and quantum effects explains why phosphorene does not support hyperbolic surface plasmon polaritons. This highlights the importance of going beyond simple models when studying materials that can support tightly confined plasmon-polaritons.

We explore the nonlinear optical properties of graphene and phosphorene nanoribbons using ab initio modeling and self-consistent perturbation theory. These two-dimensional materials exhibit significant potential for frequency conversion, optical modulation, and ultrafast signal processing due to their inherent nonlinear responses and tunable plasmonic characteristics. Our investigations reveal that graphene nanoribbons (GNRs) photoexcited by intense ultrashort optical pulses exhibit strong transient nonlinear optical responses driven by thermally activated plasmons, demonstrating a robust, non-invasive method for achieving tunable nonlinear effects without the need for excessive charge carrier doping. In a parallel study, we investigate enhanced nonlinear interactions in nanoribbon heterostructures, where the synergetic combination of tunable plasmons and anharmonic electron dispersion in graphene and phosphorene offers unique opportunities for device engineering.

Heavily doped semiconductors have emerged as an enabling platform for mid-infrared photonics, leveraging free electrons to achieve strong and tunable nonlocal-nonlinear light-matter interactions. In this talk, we will discuss recent theoretical and experimental studies on third harmonic generation and Kerr nonlinearity in heavily doped semiconductors, in which hydrodynamic contributions dominate.

In this presentation, the aluminium oxide integrated photonics platform will be presented, as well as some examples on how it can enable next generation quantum technology.

Modulated free electrons are emerging as powerful tools in quantum science, offering exceptional spatial, spectral, and temporal resolution. Beyond their role as high-precision probes, recent advances have highlighted their potential for quantum control, enabling coherent manipulation of light–matter systems. In this work, we explore how the quantum degrees of freedom of modulated electron wavepackets can be harnessed for both preparation and readout of quantum states in targets ranging from single quantum emitters to hybrid polaritonic systems. For quantum emitters, we show that periodic electron combs induce Rabi-like dynamics without entanglement, preserving state purity. We identify regimes where realistic modulations retain this behavior, enabling robust state preparation, and propose a protocol for full density matrix reconstruction that relies on the electron's coherence. We then extend our analysis to polaritonic targets, revealing how modulated electrons coherently interact with their complex excitation landscape. This enables both spectral probing via techniques like electron-energy-loss and cathodoluminescence spectroscopy, and active quantum control in the strong-coupling regime. These results position modulated electrons as versatile quantum resources for probing and controlling a broad range of light–matter platforms.

Group-IV colour centres in diamond, such as tin-vacancy (SnV) centres, are emerging candidates for quantum technologies [1]. Especially with their inversion-symmetric crystallographic structure, providing excellent optical characteristics [2], resilience to electrical noise, and an efficient spin-photon interface with narrow zero-phonon-line (ZPL) emission [3]. However, ion implantation significantly damages the diamond lattice [4], requiring annealing to restore crystallinity and activate the colour centres [5]. Femtosecond laser annealing is an emerging technique for enhancing the activation yield; however, with ultrashort and high-intensity pulse irradiation, diamond-to-graphite transformation is reported to be more likely under such non-thermal heating mechanisms [8]. Both high-fluence blanket-implanted and single-ion-implanted diamond samples are annealed by laser treatment of unfocused femtosecond laser pulses at 400 and 800 nm wavelengths, 60 fs pulse duration, 1.4 kHz pulse repetition rate, and varying multi-pulse fluence values. Two-dimensional photoluminescence scans, photoluminescence spectrum, Raman spectroscopy, and optically detected magnetic resonance (ODMR) measurements are being used to evaluate activation efficiency. To validate the experimental results, we are also exploring and developing a two-temperature model (TTM) [9] with COMSOL Multiphysics ® to simulate the energy exchange between electron and lattice subsystems isolated under ultrashort pulse irradiation [10].

Semiconductor lasers are very sensitive to optical feedback. Here we study experimentally the effect of optical feedback on the spatial coherence of a diode laser using the speckle technique. Speckle is a noisy structure arising from the interference of coherent waves as they propagate through a diffusive medium. Using a multimode fibre as the diffusive medium, we observe that, during the laser turn-on, without feedback, the speckle contrast increases gradually (revealing a gradual increase in spatial coherence), but, with sufficiently strong feedback, the speckle contrast increases sharply (revealing an abrupt increase in spatial coherence). For pump currents above the threshold, high-contrast regions alternate with low-contrast regions. We also observe that, under appropriate current modulation, high-contrast regions are suppressed. Our findings may find application in laser-based illumination systems, because optical feedback can be used in combination with current modulation to reduce speckles over a wide range of pump currents.

We study the relaxation behavior of an optical cavity with

memory in its nonlinear response. We show that the relaxation time of

the optical cavity with memory is mostly dominated by the timescale

of the thermal relaxation of the nonlinearity. However, when crossing

a bifurcation into the bistable regime, we observe slowing down of the

optical response by several orders of magnitude compared to the ther-

mal relaxation time. Experimentally, this slowing down was verified

using an oil-filled cavity.

The ability to detect near infrared light has important applications in telecoms, medical diagnostics and remote sensing. Traditional free-space up-conversion systems based on bulk crystals are not suitable for integration purposes, due to their large footprint. Here, we employ a nonlocal dielectric metasurface as an ultra-thin up-converter, by exploiting quasi-bound states in the continuum to increase the conversion efficiency of the nonlinear process.

We demonstrate a quantum interface that simultaneously converts the wavelength, bandwidth, and duration of single-photon-level pulses, enabling compatibility between disparate quantum systems. Using difference frequency generation in a lithium niobate waveguide driven by a highly chirped pump, we transform pulses from 798 nm, 5 GHz, 150 ps (quantum dot-like) to 1300 nm, 35 GHz, < 25 ps (telecom standard). This nonlinear optical time lens achieves over 80% internal conversion efficiency and compresses output pulses below detector resolution. The device offers a compact solution for integrating quantum emitters, memories, and telecom networks, with potential for further pulse shape control.

We present experimental and theoretical representation of quantum-like Schrödinger's cat states, by exploiting orbital angular momentum of the light. We investigated complex superposition as 3-Cat, 6-Cat and Fock-Cat states.

Optical microcavities have emerged as a powerful platform for investigating fundamental aspects of non-relativistic quantum mechanics, owing to recent advances in controlling the transverse state of light in these systems. We recently employed this platform to explore a long-standing question in quantum tunnelling. While quantum tunnelling has been studied since the early days of quantum mechanics, certain aspects—particularly the duration of tunnelling events—remain contentious.

In our experiment, we examine the motion of two-dimensional photons within a system of two coupled waveguide potentials, imprinted as a height profile on one of the cavity mirrors. In this system, the transfer of population between the waveguides serves as a clock, allowing us to measure particle speeds along the waveguide axis.

Applying this technique to exponentially decaying quantum states at a reflective potential step, we establish an energy-speed relationship for tunnelling particles. Our results reveal that lower-energy particles exhibit higher measured speeds within the potential step. These findings contribute to the discourse on tunnelling times and, independently, serve as a test of Bohmian trajectories in quantum mechanics. Regarding the latter, our observed energy-speed relationship is found to be inconsistent with the particle dynamics predicted by the guiding equation in Bohmian mechanics.

Second-order nonlinear optical materials with high refractive index and wide transparency range are of high demand for various photonic applications. Here, we present nanostructures fabricated in wafer-bonded crystalline aluminum indium phosphide (AlInP). The nanostructures exhibit strong enhancement of second-harmonic generation due to higher-order anapole excitations. Our results illustrate the potential of AlInP for nonlinear nanophotonics.

Terahertz technologies offer unique advantages for communication, sensing, and imaging, yet integrated platforms struggle to perform efficiently in this range. Thin-film lithium niobate, a nonlinear photonic platform, enables compact, broadband, and high-speed terahertz sources through efficient frequency conversion. In this talk, I present our progress on developing sub-terahertz continuous-wave sources on lithium niobate chips, aiming to bridge the gap between electronic and photonic systems for next-generation terahertz integration.

We have observed for the first time a parametric down conversion process within a solitonic waveguide. This feature ensures an optimal mode-overlapping between the interacting waves. Moreover, the excited photorefractive nonlinearity enables a phase-locking regime that allows the temporal overlapping of the interacting pulses too. A broadband PDC is then possible within a waveguide without special needs for phase-matching and temporal sinchronisation.

Traditionally, the resolution of optical microscopes is limited to about half the wavelength used. Single-Molecule Localization Microscopy (SMLM) achieves super-resolution by isolating blinking fluorophores across multiple acquisition frames, reaching resolutions down to single nanometers. However, high-density samples present challenges, as overlapping point spread functions (PSFs) limit accurate localization with conventional, e.g. sCMOS, detectors. Single-Photon Avalanche Diode (SPAD) arrays offer new quantum correlation-enhanced techniques to improve detection sensitivity and emitter density resolution in SMLM. Here, we demonstrate a photon-correlation-based approach for multi-emitter fitting and high-density SMLM in a scanning configuration.

A 23-pixel SPAD array with integrated time-correlated photon counting is used as the detector in a fluorescence confocal-scanning microscope. Crucially, fluorophores are single-photon emitters. The photon arrival times are used to compute the second-order quantum correlation of the signal, which is directly related to the number of emitters in the scanning location. This information makes it possible to locate fluorophores with overlapping point spread functions, consequently, SPAD arrays provide the ability to image in high emitter densities, which enables faster data acquisition and dynamic imaging.

We study the driven-dissipative dynamics of one-dimensional photonic resonator arrays functioning as broadband quantum amplifiers [1,2]. We first analyze linear resonators with incoherent pumping, complex nearest-neighbor hopping, and dissipation. We identify conditions for a steady-state topological phase with broken time-reversal symmetry, where photonic signals propagating along the array are directionally amplified. Remarkably, this amplification is topologically protected against disorder, broadband, and near quantum-limited, with gain growing exponentially with system size [2].

We then explore the realization of such topological amplification using coupled Kerr-nonlinear resonators driven by a coherent pump with linearly increasing phase [3]. This induces parametric couplings with complex phases inherited from the pump, breaking time-reversal symmetry and enabling topological amplification via four-wave mixing. Exploiting non-linearities, we thus alleviate the need for incoherent pumping or Floquet engineering. We characterize the rich topological phase diagram [4] and the non-linear dynamics of the emergent topological phase transition [5]. Finally, we propose a microwave implementation using Josephson junction arrays, predicting high directional amplification performance with current technology [3].

[1] Porras et al. PRL 122, 143901 (2019).

[2] Ramos et al. PRA 103, 033513 (2021).

[3] Ramos et al. arXiv:2207.13728 (2024).

[4] Gómez-León et al. Quantum 7, 1016 (2023).

[5] Rassaert et al. arXiv:2411.08965 (2024).

TBA

\abstract{Quantum correlations, particularly squeezing and entanglement, are essential in quantum technologies such as metrology, computation, and simulation, as well as in foundational studies. In quantum optics, these phenomena are often intertwined: two squeezed beams can be transformed into entangled beams by mixing them at a beam splitter, and vice versa. However, it is less common to encounter states where two beams are simultaneously squeezed individually while retaining global entanglement. These hybrid states evidently present potential possibilities for applications. In this work, we propose a compact single-cavity source based on a nondegenerate optical parametric oscillator operated below threshold, capable of generating such light—signal and idler beams that are quadrature-squeezed individually while maintaining global entanglement. This behavior arises from an additional linear coupling between the signal and idler, resembling a beam-splitter interaction. We discuss two physical implementations of this system: one based on intra-cavity electro-optic modulators and the other on optomechanical interactions. This unique combination of local and non-local quantum correlations opens the door to novel quantum communication and metrology protocols.}

We performed an experimental and numerical study of an Indium Phosphide photonic integrated circuit designed for quantum random number generation. We investigated the dynamics of two weakly mutually coupled semiconductor lasers and the transient evolution towards the synchronization of the lasers’ optical phases. The simulated dynamics with the experimentally adjusted parameters were found to be in qualitatively good agreement with the experimental time traces. The results provide a better understanding of the evolution towards synchronization and a foundation for the optimization of the photonic quantum random number generation system.

Exciton-polaritons are hybrid light–matter quasiparticles that arise from the strong coupling between excitonic resonances and confined optical modes in microcavities. While foundational studies have primarily focused on GaAs-based heterostructures, the emergence of two-dimensional semiconductors—such as transition metal dichalcogenide (TMD) monolayers and layered perovskites—has opened new avenues for exploring polariton physics in novel material and photonic regimes.

This presentation focuses on the simultaneous enhancement of light–matter coupling and polariton nonlinearities by engineering both the electromagnetic environment and the excitonic properties of the active materials. Coupling efficiency and interaction strength are further improved through unconventional cavity designs that leverage phenomena such as surface optical modes and bound states in the continuum, as well as through material innovations like suspended monolayers and single-crystal layered perovskites.

The results establish 2D polariton systems as promising platforms for fundamental investigations in the strong and ultrastrong coupling regimes, as well as for the development of integrated photonic technologies for classical and quantum information processing.

We demonstrate a nonlinear AlGaAs photonic chip generating biphotons with high-dimensional spatial correlations. Photon pairs are generated by parametric down conversion in a waveguide array and simultaneously spread through quantum walks along the various waveguides, allowing to generate various types of high-dimensional entangled states of light. We further implement the Su-Schriefer-Heeger model and demonstrate the topological protection of the SPDC process against disorder. These results highlight nonlinear waveguide arrays as a promising platform for exploring the interplay between nonlinearity, disorder and topology in quantum photonic circuits.

Lithium niobate-on-insulator (LNOI) has emerged as a cornerstone for on-chip nonlinear optics, combining strong second-order nonlinearity with low-loss waveguides and nanofabrication compatibility. We demonstrate compact and efficient optical frequency converters built on a 4-inch LNOI wafer. Using an optimized process—integrating waveguide definition with post-etch domain inversion—we realize second-harmonic generation (SHG) with on-chip efficiency approaching 90%. This performance benefits from quasi-phase matching (QPM), tight optical confinement, and smooth waveguide sidewalls. Compared to traditional chip-scale approaches, our method offers improved manufacturability and consistency without compromising nonlinear efficiency. The devices are well suited for scalable integration in systems for frequency translation, amplification, and quantum light generation.

Bragg Scattering Four-Wave mixing (BS-FWM) is used in fibers to frequency shift single photons. The main limitation of this nonlinear process is the phase-matching requirement. In this work, we investigate how this condition can be controlled by changing the fiber temperature. We then are able to optimize the efficiency of the BS-FWM process for selected wavelengths. This tunability by temperature is beneficial for fiber-based actively multiplexed single photons sources : it is possible to generate photons and shift their frequency with the same fiber and wavelengths involved.

We contrast the self-organization of light in a nonlinear optical cavity against the recently introduced theory of self-organized bistability (SOB). This reveals that the nonlinear optical cavity may serve as a platform for the first experimental realization of SOB and drives further research into information processing in nonlinear optical cavities.