Conference Agenda

Compute energy-delay performance is today communication limited. The scaling vectors of cost, bandwidth density and energy are challenged by the physical limits of electronic interconnect bandwidth. The emergence of foundry compatible silicon photonics solutions promises to relieve this roadblock with electronic-photonic integration at the package level. These solutions, as described in the recent release of the 2023 Integrated Photonics System Roadmap – International, will be review with a focus on materials, tools and processes for sustainable system performance scaling.

Silicon photonics subwavelength metamaterials have found use in of applications ranging from optical communications to sensing. In this invited talk, we review some of the latest advances in the field.

Photonic integrated biosensors have garnered considerable attention due to their promising applications in various fields such as healthcare. Differentiating specific targets from interfering background effects is a challenging task. In this work, a dual-polarization Mach-Zehnder interferometer (MZI) with coherent phase readout is proposed to identify refractive index changes from different layers above the waveguide surface, thus improving sensor specificity. All the system building blocks have been designed for a 300 nm-thick silicon nitride platform, fabricated and characterized. The first experimental results show a bulk waveguide sensitivity of 0.17 RIU/RIU for TE polarization and 0.25 RIU/RIU for TM, confirming the correct functioning of the sensors when operating for each polarization separately. Future work will focus on simultaneous sensing with both polarizations and experiments with layered variation of refractive indices.

Phase-based sensing can reach a very high level of accuracy, and integrating these devices on a silicon chip can make these devices extremely compact and very affordable. In this presentation, I will report some recent results of photonic sensing on chip using phase-based measurements. In particular, I will show demonstrations of integrated wavemeters on chip at high speed using carrier-depletion-based modulation, and refractive index sensing experiments based on actively-modulated interferometers.

We report recent progress on optoelectronic devices and metasurfaces involving surface plasmons, enabled by metal-oxide-semiconductor (MOS) structures on Si and on epsilon-near-zero materials. We discuss electrically tuneable metasurfaces, high-speed electro-absorption modulators, and reflection modulators. Hot carriers created by the absorption of plasmons in metallic nanostructures on MOS structures are also discussed as they lead to novel device physics that open the door to new device concepts.

Subwavelength engineering has become established as an essential design tool in integrated photonics. The utilization of state-of-the-art semiconductor manufacturing methods to create nanostructures within optical waveguides has provided unparalleled control over the manipulation of light propagation in silicon photonic chips. In this presentation, we will present our recent breakthroughs in this rapidly advancing field. We will also introduce a nascent research area of resonant integrated photonics, leveraging Mie resonances in dielectrics for on-chip guidance of optical waves, as well as Dirac gratings and parity-time symmetric waveguide structures.

Hybrid photonic devices, harnessing the advantages of multiple materials while mitigating their respective weaknesses, represent a promising solution to the effective on-chip integration of generation and manipulation of non-classical states of light encoding quantum information. We demonstrate a hybrid III-V/Silicon quantum photonic device combining the strong second-order nonlinearity and compliance with electrical pumping of the III-V semiconductor platform with the high maturity and CMOS compatibility of the silicon photonic platform. Our device embeds the spontaneous parametric down-conversion (SPDC) of photon pairs into an AlGaAs source and their subsequent routing to a silicon-on-insulator circuitry. This enables the on-chip generation of broadband telecom photon pairs by type 0 and type 2 SPDC from the hybrid device, at room temperature and with strong rejection of the pump beam. Two-photon interference with 92% visibility proves the high energy-time entanglement quality characterizing the produced quantum state, thereby enabling a wide range of quantum information applications.

Nonlocal correlations exhibited by quantum systems are fundamental for secure remote quantum information tasks and tests of fundamental quantum physics. Bell nonlocality is highly susceptible to noise, which degrades the quality of nonlocal correlations, leading to the existence of Bell local states. These mixed entangled states cannot display nonlocality in a standard Bell scenario. Here we experimentally demonstrate that single copies of Bell local states can demonstrate nonlocal behavior when integrated into a multi-partite photonic network.

Molecular polaritons are hybrid light-matter states that emerge when a molecular transition strongly interacts with photons in a resonator. At optical frequencies, this interaction unlocks a way to explore and control new chemical phenomena at the nanoscale. Achieving such control at ultrafast timescales, however, is an outstanding challenge, as it requires a deep understanding of the dynamics of the collectively coupled molecular excitation and the light modes. Here, we investigate the dynamics of collective polariton states, realized by coupling molecular photoswitches to optically anisotropic plasmonic nanoantennas. Pump-probe experiments reveal an ultrafast collapse of polaritons to pure molecular transition triggered by femtosecond-pulse excitation at room temperature. Through a synergistic combination of experiments and quantum mechanical modelling, we show that the response of the system is governed by intramolecular dynamics, occurring one order of magnitude faster with respect to the uncoupled excited molecule relaxation to the ground state.

In quantum mechanics, the precision achieved in parameter estimation using a quantum state as a probe is determined by the measurement strategy employed. The quantum precision limit, a fundamental boundary, is defined by the intrinsic characteristics of the state and its dynamics. Theoretical results have revealed that in interference measurements with two possible outcomes, like the Hong Ou-Mandel interference, this limit can be reached under ideal conditions of perfect visibility and zero losses. However, this cannot be achieved in practice, so precision never reaches the quantum limit. But how do experimental setups approach precision limits under realistic circumstances?

In this work, we provide a general model for precision limits in two-photon Hong-Ou-Mandel interferometry for non-perfect visibility and validate it experimentally using different quantum states. A remarkable ratio of 0.97 between the experimental precision and the quantum limit is observed, establishing a new benchmark in the field.

Photonic integrated circuits (PICs) based on silicon-on-insulator (SOI) substrates provide a lightweight, compact platform for applications in quantum optics. We show the evaluation and characterization of an SOI-based PIC design for an entangled photon pair source, generating photon pairs by means of the nonlinear process of spontaneous four-wave mixing in microring resonators. Experimental results following from the chip fabrication fed back into the simulated parameter tuning effects, culminating in photon pair generation with measured correlations exceeding classically predicted limits.

Photonic Orbital Angular Momentum (OAM) is becoming a pertinent quantum variable for atom-light interaction, in particular for non-linear interaction which leads to photon entanglement and OAM-entanglement. With two 4-levels atomic schemes, we show that Four Wave Mixing addressed by vortex beams leads to very different OAM-entanglement especially for large OAM values.

Nonlinear photonic systems are a promising platform for photonic reservoir computing due to their high bandwidth, parallelism and low power consumption. These devices can potentially enhance or, in some scenarios, replace CMOS-based electronic computing systems. However, a significant challenge lies in the limited scalability of photonic technologies that rely on one-to-one implementations of artificial neurons or logic gates. In this presentation, we will present our research on complexity-driven neuromorphic photonic systems, where complex nonlinear interactions among thousands of optical waves within single optical components drive information processing. Specifically, we will discuss how the nonlinear interactions between optical waves, crucial for efficient photonic reservoir computing, can be adjusted and controlled in gain systems such as integrated lasers or doped fibres. This fine-tuning aims to optimise the system's performance and identify an optimal "complexity" threshold for learning.

In the framework of optical frequency conversion, metasurfaces have elevated the potential for effective interfacial nonlinear coefficients through various modes of field localization. For the generation of pulsed ultrafast terahertz (THz) signals, metasurfaces present a viable alternative in the domain of surface-scalable sources driven by low-power oscillators (using nJ pulses). However, recent innovations have predominantly relied on surface plasmons (metals) and, more broadly, on excitations within non-transparency windows—conditions that typically impose limitations on applications and the choice of platforms. Here, we demonstrate the utilization of a fully-dielectric, fully transparent semiconductor that exploits surface-nano-structure-mediated resonances alongside its inherent quadratic nonlinear response. Our system exhibits a remarkable 40-fold efficiency enhancement in comparison to the non-decorated substrate.

We theoretically demonstrate the generation of clean few-cycle pulses in a three-stage all-bulk multipass cell scheme. By meticulously selecting the number of round trips and the width of the material used in each cell, we are able to keep the three stages in the enhanced frequency chirp regime. The results show the generation of short and clean pulses, with compression factors approaching 50 with a final duration below 1.5 cycles.

Whispering-gallery-modes resonators (WGMR) are effective switching devices when either coated or filled with non-linear material. We present examples of all-optical switching of hybrid WGM using polyfluorene, a methacrylate azobenzene and an acrylate derivates. We have studied the Kerr non-linear effect and thermal nonlinearities in a such hybrid systems.

We propose an AlGaAs microring resonator design for the generation of an optical frequency comb by means of the interplay between harmonic generation and Kerr effect. Modal phase matching imposes specific waveguide geometries and, consequently, it impacts the nonlinear efficiency of the system. We show the dynamics of χ(2) + χ(3) comb generation resulting from type-I modal phase matching.

In this paper, we introduce a secure optical communication protocol that harnesses quantum correlation within entangled photon pairs. A message written by acting on one of the photons can be read exclusively through measurements of the other photon of the pair. In this scheme, a bright, meaningless optical beam hides the message, rendering it inaccessible to potential eavesdroppers. Unlike traditional methods, our approach only affects unauthorized users, fundamentally limiting their access to the communication channel. We demonstrate the effectiveness of our protocol by achieving secure communication through both amplitude and phase modulation, relying on single-photon measurements, as opposed to most approaches which rely on coincidence measurements. We successfully demonstrate the resilience of the data transfer to noise up to 10^5 times greater than the signal, and we employ this technique for the secure transfer of an image.

We develop a framework that computes two-photon spontaneous emission (TPSE) spectra of a quantum emitter near an arbitrarily shaped nanostructure. The model considers the interaction up to the electric quadrupolar order, which is relevant for nanophotonic structures sustaining strongly confined fields that are used to enhance and to tailor spontaneous emission processes. Moreover, we consider interference effects between multipolar two-photon emission channels, for the first time to our knowledge. First, we show for a s → s transition of a hydrogen atom placed under a silver plasmonic nanodisk a substantial enhancement in the photon-pair emission rates by 5 and 11 orders of magnitude for the two-electric dipole (2ED) and two-electric quadrupole (2EQ) transitions, respectively. Then for the same emitter under a plasmonic graphene nanotriangle, we demonstrate a breakdown of the electric dipole approximation in the TPSE process where the interference between the 2ED and 2EQ transitions is important, as it increases the total rate by 63 %. Third, we explore platforms where entangled photons of different energy are emitted in the far-field in different directions. In the end, our framework is a complete tool to design emitters and nanostructures for the TPSE process, leading to a rich assortment of functional nanoantennas.

Non-Hermitian photonics attracted significant attention as a rising field in optics due to the emergence of numerous physical concepts and novel effects. Unlike systems described by a Hermitian Hamiltonian, where hermiticity ensures system closure to the environment and energy conservation, a non-Hermitian system enables the description of open systems and facilitates understanding of how a system can interact with the environment. We propose an innovative approach for simulating non-Hermitian dynamics by realizing a non-unitary photonic quantum walk, based on a light beam propagating in free space and manipulated via step operators acting jointly on its polarization and transverse momentum. We use the latter degrees of freedom to encode the coin and walker systems, respectively. To induce coin-rotation, we utilize a uniform liquid-crystal (LC) plate. An LC dichroic polarization grating is used instead to obtain a coin-dependent non-unitary translation operation on the walker. Through the combination of liquid crystals and dichroic absorbing dyes, we can manipulate both polarization and light amplitude. This development yields a compact and versatile platform that significantly expands the scope of photonic simulations in studying quantum dynamics. It introduces a new dimension for manipulating topological states, potentially enabling the observation of phenomena related to non-Hermitian topological phases.

Photonic circuits that can manipulate light in a unitary and reconfigurable way are promising candidates for optical processing of both classical and quantum information. However, engineering such circuits poses significant challenges in terms of minimizing losses, increasing the number of modes, and achieving multidimensional dynamics.

Here we present a novel photonic circuit based on spin-orbit photonics that, by realizing up to 20 timesteps of a two-dimensional quantum walk, couples a single input mode to hundreds of output modes. Our circuit consists of three liquid crystals metasurfaces that perform periodic and space-dependent polarization transformations on a light beam, effectively coupling circularly polarized spatial modes with different transverse momenta. These modes form the basis of a two-dimensional lattice where the quantum walk takes place.

We demonstrate the versatility and scalability of our circuit by operating it in different regimes and measuring the output modes distributions, which show high similarity with the theoretical predictions (>87%).

The development of modern spintronics materials require novel characterization tools capable of characterizing nanometer-sized spin textures. Neutrons are a convenient probe for this task due to their angstrom-sized wavelengths, electric neutrality and robustly controllable spin state. Recent research has focused on enabling access to new degrees of freedom in order to provide a neutron toolbox capable of characterizing emerging materials. This includes the development of holographic and tomographic techniques for characterizing the 3D bulk spin textures and the techniques for creating structured neutron beams with helical and skyrmion-like spin-orbit states. Here we provide a concise overview of this work and discuss future prospects and applications.

By combining the concepts of structured light and quantum interference, we design and experimentally demonstrate a simple and robust scheme that tailors quantum interference to engineer photonic states with spatially structured coalescence along the transverse profile. To achieve this, we locally tune distinguishability of a photon pair by spatially structuring the polarisation and creating a structured quantum eraser.

Nonlocality in quantum systems is fundamental for secure remote quantum information tasks and tests of fundamental quantum physics. While loophole-free nonlocality verification has been achieved with polarization-entangled photon pairs, extending this to other degrees of freedom remains challenging. Here, we demonstrate detection loophole-free quantum steering utilizing optical vector vortex states, which are formed by combining orbital angular momentum (OAM) and polarization. This advancement goes beyond traditional polarization encoding, opening avenues for secure quantum communication devices and device-independent protocols in free-space and satellite-based scenarios.

Encoding information in time-bin entangled photonic systems enables the implementation of quantum technologies that are compatible with both integrated and fiber frameworks. Extending such an encoding to high-dimensional (qudit) time-bin entanglement provides a tool towards scaling the information capacity, noise resilience, and scalability of information processing. Here, we demonstrate scalable time-bin entangled qudits in a programmable photonic chip, as well as in a fully fibered coupled loop system.

We study the spatiotemporal dynamics of asymmetric microcavity semiconductor lasers as function of the resonator geometry. Our experimental and numerical studies elucidate how the classical ray dynamics, dictated by the cavity geometry, affects nonlinear light-matter interaction, which in turn determines lasing dynamics. Our approach to engineering laser dynamics is robust, compact, and has the potential to be applied to controlling other nonlinear complex systems.

We demonstrate a novel and straightforward approach to enhance the nonlinear responses of metamaterials by incorporating them into multipass cells, allowing the pump beam to interact with the metasurface multiple times. As a proof of principle, we achieved phase matching of the second-harmonic generation (SHG) signal with a superlinear dependence on the number of passes. Experimentally, we observed a remarkable tenfold enhancement in the SHG signal from a plasmonic metasurface after nine passes.This approach is generic and compatible with various existing enhancement techniques and metamaterials, offering a versatile method to improve the performance of nonlinear devices.

Recently, superradiant bursts of light have been experimentally observed for a cascaded quantum system. This was realized using an ensemble of waveguide-coupled two-level atoms that exhibit propagation direction-dependent coupling to the waveguide mode. Here, we experimentally study the collective radiative decay of a fully inverted atomic ensemble and measure the second-order correlation function, g^(2)(t1,t2), of the light emitted by the atoms into the waveguide. We observe a g^(2)(0,0) of about 2 at the beginning of the decay, followed by a decrease to g^(2)(t,t) to 1 (where t>0) within the characteristic time scale of the burst dynamics. This built-up of second-order coherence can be interpreted by assuming that, following an initially independent emission, the atoms synchronize during their decay. Interestingly, for ensembles below and above full inversion, g^(2)(t,t)=1 for all times. In addition to these observations, we find an anti-correlation of photon detection events, i.e., g^(2)(t1,t2)<1, in certain parameter regions in which t1 unequal to t2, indicating a temporal sub-structure of the light emerging the ensemble. Our findings can be well described with a model based on the truncated Wigner approximation. Our results contribute to understanding the fundamentals of light-matter interaction and help engineering protocols for the generation of non-classical light.

The Advanced Laser Light Source (ALLS) laboratory provides high-repetition-rate ultrashort light pulses using ytterbium laser technology. Recently, we have developed a novel end-station called time- and angle-resolved photoemission (TR-ARPES) to explore the rapid electron dynamics in quantum materials when subjected to intense optical excitation in the near- and mid-infrared range. These intense pulses are generated using our in-house-built optical parametric amplifier (OPA) ranging from 1.6 to 8 μm with a duration of around 100 fs

Recent years have witnessed remarkable progress in enhancing the supercontinuum (SC) generation in highly nonlinear photonic integrated waveguides. In this study, we conduct a comprehensive investigation into supercontinuum (SC) generation in high-index doped silica glass integrated waveguides. We explore a variety of femtosecond pumping wavelengths and input polarization states, demonstrating coherent octave-spanning SC bandwidth from visible to mid-infrared wavelengths.