Electron Beam-Induced Deposition (EBID) enables site-specific nanofabrication but suffers from significant carbon contamination, limiting its applicability in plasmonics, nanoelectronics, and sensing. In this study, we investigate the relationship between EBID process parameters such as beam current, acceleration voltage, and dwell time, and the platinum-to-carbon composition of deposited nanostructures. Using Energy Dispersive X-Ray Spectroscopy (EDX), we establish a hindered exponential growth model that correlates deposit composition with fabrication conditions. To enhance metal purity, we apply plasma oxygen treatment, exposing EBID deposits to a 30 W plasma for 30 minutes in a tabletop plasma generator. Post-treatment EDX analysis confirms a systematic increase in platinum content, while SEM inspection reveals nanostructure shrinkage due to carbon removal. This work aims to provide a framework for optimizing EBID fabrication and post-processing strategies to enhance material performance.

The Hawking effect amplifies fluctuations in the vicinity of horizons, both in black holes and in analogue platforms. Here, we consider a polariton simulator and numerically examine the stimulated Hawking effect using a coherent probe incident on the horizon from the exterior. We implement an experimentally realistic effective spacetime that supports a quasinormal mode (QNM) in the vicinity of the horizon. We find that the stimulated Hawking effect manifests as transmission into a negative-energy Bogoliubov channel inside the horizon, consistent with pseudo-unitary Bogoliubov scattering. Moreover, transmission across the horizon peaks at the QNM frequency. The computed spectral signatures provide a practical guide for future experimental investigations of the Hawking effect and its interplay with QNMs, an open question in quantum field theory in curved spacetime.

The Hawking effect – the spontaneous emission of correlated quanta from horizons – can be observed in laboratory systems where an acoustic horizon forms when a fluid transitions from subcritical to supercritical flow. Although most theoretical and experimental studies have relied on real-space observables, the frequency-dependent nature of the Hawking process motivates a momentum-space analysis to access its spectral structure and entanglement features. Here, we numerically compute the momentum-space two-point correlation function in a quantum fluid using the truncated Wigner approximation, a general method applicable to both conservative and driven-dissipative systems. We consider a polaritonic fluid of light in a realistic configuration known to yield strong real-space correlations between Hawking, partner, and witness modes. We find signatures that are directly accessible in state-of-the-art experiments and offer a robust diagnostic of spontaneous emission. Our results form the basis for a new theoretical framework to assess a variety of effects, such as quasi-normal mode emission or modifications of the horizon structure on the Hawking spectrum.

Monitoring local brain temperature with high spatial precision is essential to understanding neurophysiological processes and managing the side effects of optical neuromodulation techniques. We present a novel multifunctional neural interface integrating a microscale resistance temperature detector (µRTD) onto the curved surface of a tapered optical fiber (TF), enabling co-localized light delivery and thermal sensing with minimal footprint. The µRTD, patterned via an unconventional two-photon polymerization (TPP)-based process on the fiber surface, exhibits thermal sensitivity <0.1°C and low self-heating under physiologically-safe bias conditions. We demonstrate the system's capacity to resolve subtle temperature changes induced by optogenetic stimulation/inhibition protocols (the latter requiring illumination periods of hundreds of milliseconds up to several seconds), revealing significant thermal accumulation only under long, high-intensity illumination. This integration resolves the spatial mismatch of multimodal probes and reduces implant cross-section compared to coaxial or side-by-side configurations. Furthermore, the TPP approach is modular, allowing integration with additional functionalities (i.e., electrophysiological recording or thermoplasmonics). By uniting photonic and thermal readout into a minimally invasive probe, our technology offers a powerful tool for studying thermally mediated neural processes, enhancing the safety and interpretability of optical neurotechnologies. Its integration potential positions this platform as a complementary technology for next-generation multifunctional neural interfaces.

A superfluid flows without friction below a critical velocity, exhibiting zero drag force on impurities. Above this threshold, superfluidity breaks down, and the internal energy is redistributed into incoherent excitations such as vortices. We demonstrate that a mobile, finite-mass impurity immersed in a flowing two-dimensional paraxial superfluid of light can swim against the superfluid current when the critical velocity is exceeded. This self-propulsion is achieved by the periodic emission of vortex-antivortex pairs downstream, which impart an upstream recoil momentum that results in a net propulsive force. Analogous to biological systems that minimize effort by exploiting wake turbulence, the impurity harnesses this vortex backreaction as a passive mechanism of locomotion. Based on a simple theoretical model, we quantitatively describe how this mechanism depends on the impurity geometry and the surrounding flow velocity. Our findings establish a fundamental link between internal-energy dissipation in quantum fluids and concepts of self-propulsion in active-matter systems and open new possibilities for exploiting quantum vortices for controlled transport at the microscale.

Weakly-interacting many-body systems possess remarkable quantum properties that are essential components of quantum technologies, and constitute a topic of fundamental interest. Here we show that in a solid-state nonlinear microcavity embedding discrete modes of exciton-dressed photons, we can isolate a single eigenmode of quantum fluctuations from the much brighter coherent fraction of the field. In this regime, we perform frequency- and time-resolved correlations measurements between photons on the red and blue side of the fluctuations spectrum. When the average number of fluctuation quanta is smaller than one, we observe the formation of large pairwise time-ordered correlations: red photon first and blue photon second. We show that this peculiar time-ordering correlation emerges spontaneously from the interplay between frequency-resolved detection, and the non-trivial internal quantum structure of the elementary fluctuations.

The ability to efficiently characterize optical quantum states is essential for the development of quantum technologies. While traditional approaches to perform quantum state tomography are often experimentally demanding, neuromorphic architectures provide an attractive alternative. In this work, we demonstrate that a quantum nonlinear driven-dissipative mode is sufficient to act as a quantum reservoir. We show that training with the optical emission spectrum alone is sufficient to characterize the quadrature angle and squeezing strength of continuous wave squeezed states. We demonstrate how the method works for a finite-bandwidth squeezed source (e.g., a degenerate optical parametric oscillator) processed by a nonlinear polariton microcavity, highlighting its transferability. These results suggest a scalable and experimentally frugal path to characterizing nonclassical states with nonlinear optical systems.

In the search for materials for quantum information science applications, colloidal semiconductor nanoplatelets (NPLs) have emerged as a highly promising class of materials due to their interesting optical properties, such as narrow emission line widths and fast photoluminescence (PL) lifetimes at room temperature. So far, only a few works focused on the quantum properties of their emission; however, NPLs, with their atomic-scale thickness and one-dimensional quantum confinement, are promising candidates for single-photon sources. Here, we demonstrate room-temperature single-photon emission from core/shell CdSe/ZnS NPLs, which feature an 8 × 20 nm2 surface area and 1 nm shell. The limited surface area ensures effective Auger nonradiative recombination, resulting in highly efficient single-photon generation with values of photon purity as low as g(2)(0) = 0.04. The observed long-period blinking and bleaching typical of such thin shells can be easily reduced by increasing the shell thickness. This work establishes NPLs as single-photon sources that are very well suited for integration into quantum photonic systems.

Second-order phase transitions are governed by spontaneous symmetry breaking, which yield collective excitations with a gapless spectrum called Nambu-Goldstone (NG) modes. While NG modes in conservative systems are propagating excitations, non-equilibrium phase transitions have been predicted to feature a diffusive NG mode. We present the first experimental evidence of a diffusive NG mode in a non-equilibrium Bose-Einstein condensate of microcavity polaritons. The NG mode is observed as a spectral narrowing in the spectroscopic response of the condensate. Additionally, explicitly breaking the symmetry causes the opening of a gap in the spectrum and the disappearance of the NG mode. Our observations confirm the diffusive dynamics of the NG mode of non-equilibrium phase transitions and establish a promising framework to investigate fundamental questions in statistical mechanics.

This study introduces a novel method for the deterministic fabrication of metallic nanostructures with controlled geometry and composition on suspended, single mode tapered optical nanofibers (TNFs) using a tailored Blurred Electron Beam Induced Deposition (BEBID) technique. TNFs, owing to their subwavelength diameters and intense evanescent fields, offer a unique platform for enhanced light matter interactions at the nanoscale. However, their mechanical fragility has thus far hindered the integration of plasmonic structures using conventional high energy deposition methods. BEBID addresses this limitation by deliberately defocusing the electron beam to reduce local mechanical stress, minimize vibration, and prevent fiber damage during deposition, thereby enabling the one-step growth of platinum nanopillars with sub 20 nm spatial precision and high structural fidelity directly on suspended TNFs. The fabricated structures were characterized using SEM, EDX, and their optical properties were investigated through broadband scattering spectra and polarization resolved measurements, showing strong agreement with Finite Difference Time Domain (FDTD) simulations. Numerical modeling further reveals that ordered arrays of nanopillars can shape and direct the scattered field along the fiber axis, enabling directional emission. This work establishes BEBID as a versatile bottom up nanofabrication approach for functional photonic architectures on fragile substrates, with direct applications in quantum photonics, nano optics, and on fiber plasmonic sensing.

Quantum field theory (QFT) in curved spacetimes predicts the amplification of field excitations and the occurrence of classical and quantum correlations, as in the Hawking effect for example. This raises interest in experiments in which the curvature of spacetime can be controlled and amplification measured, as in fluids going from subsonic to supersonic speeds where acoustic excitations are effectively trapped inside an acoustic horizon. Quantum fluctuations of the acoustic field are predicted to yield entangled emission across the horizon, as in black holes. Here, we introduce such a QFT simulator in a one-dimensional polaritonic fluid of light. We demonstrate the unique tunability of our system by engineering smooth and steep horizons, which respectively have quasithermal, but weak, and strong Hawking radiation. We measure the spectrum on either side of the horizon and evidence the excitation of negative energy waves in fluids of light for the first time. Notably, we explicitly show that, beyond phononic excitations as in other systems, our simulator also supports excitations with a massive, relativistic dispersion. In the future, quantum optics techniques offer the possibility to measure entanglement in unexplored regimes, giving insight in this outstanding prediction of relativistic QFT.

The formation of quantized vortices is a unifying feature of quantum mechanical systems, making it a premier means for fundamental and comparative studies of different quantum fluids. Being excited states of motion, vortices are normally unstable towards relaxation into lower energy states. However, here we exploit the driven-dissipative nature of polaritonic fluids of light to create stationary, multiply charged vortices. We measure the spectrum of collective excitations and observe negative energy modes at the core and positive energy modes at large radii. Their coexistence at the same frequency normally causes the dynamical instability, but here intrinsic losses stabilize the system, allowing for phase pinning by the pump on macroscopic scales. We observe generic features of quantized vortices in quantum fluids and other rotating geometries like astrophysical compact objects, opening the way to the study of generic amplification phenomena.

The amplification of radiation by superradiance is a universal phenomenon observed in numerous physical systems. We demonstrate that superradiant scattering generates entanglement for different input states, including coherent states, thereby establishing the inherently quantum nature of this phenomenon. To put these concepts to the test, we propose a novel approach to create horizonless ergoregions, which are nonetheless dynamically stable thanks to the dissipative dynamics of a polaritonic fluid of light. We numerically simulate the system to demonstrate the creation of a stable ergoregion. Subsequently, we investigate rotational superradiance within this system, with a primary focus on entanglement generation and the possibilities for its enhancement using current techniques. Our methods permit the investigation of quantum emission by rotational superradiance in state-of-the-art experiments, in which the input state can be controlled at will.

Achieving pure single-photon emission is essential for a range of quantum technologies, from quantum computing to quantum key distribution to quantum metrology. Among solid-state quantum emitters, colloidal lead halide perovskite (LHP) nanocrystals (NCs) have attracted considerable interest due to their structural and optical properties, which make them attractive candidates for single-photon sources (SPSs). However, their practical utilization has been hampered by environment-induced instabilities. In this study, we fabricate and characterize in a systematic manner Zn-treated CsPbBr3 colloidal NCs obtained through Zn2+ ion doping at the Pb-site, demonstrating improved stability under dilution and illumination. The doped NCs exhibit high single-photon purity, reduced blinking on a submillisecond time scale, and stability of the bright state even at excitation powers well above saturation. Our findings highlight the potential of this synthesis approach to optimize the performance of LHP-based SPSs, opening up interesting prospects for their integration into nanophotonic systems for quantum technology applications.

Quantum photonics technologies, like wavelength division multiplexing (WDM), for high-rate quantum key distribution require narrowband, spectrally tunable single photon emitters. Physical methods that rely on the application of large mechanical strain to epitaxial quantum dots or electric and magnetic fields to color centers in 2D metal dichalcogenides provide limited spectral tunability. Here we adopt a chemical approach to synthesize a family of colloidal mixed-cation perovskite quantum dots (Cs1-xFAxPbBr3) that show highly photostable, compositionally tunable single photon emission at room temperature, spanning more than 30 nm in the visible wavelength spectral range. We find that tailoring the stoichiometry of the organic formamidinium (FA) cation in all-inorganic cesium lead bromide (CsPbBr3) perovskite quantum dots detunes the electronic band structure while preserving their excellent single photon emission character-istics. We argue that the mixed-cation perovskite quantum dots studied in this work offer a new platform for the realization of color-tunable single photon emitters that could be readily integrated in a diversity of quantum photonic devices.

Turbulence in quantum fluids has, surprisingly, a lot in common with its classical counterpart. Recently, cold atomic gases has emerged as a well controlled experimental platform to study turbulent dynamics. In this work, we introduce a novel system to study quantum turbulence in optics, with the major advantage of having access to a wide range of characterization tools available for light fields. In particular we report the temporal dynamics of density and phase and we show the emergence of isotropy in momentum space and the presence of different scaling laws in the incompressible kinetic energy spectrum. The microscopic origin of the algebraic exponents in the energy spectrum is discussed by studying the internal structure of quantized vortices within the healing length and their clustering at larger length scales. These results are obtained using two counter-streaming fluids of light, which allows for a precise preparation of the initial state and the in-situ measurement of the compressible and incompressible fluid velocity.

We use a recently developed high-resolution coherent probe spectroscopy method to investigate the dispersion of collective excitations of a polaritonic quantum fluid. We measure the dispersion relation with high energy and wavenumber resolution, which allows us to determine the speed of sound in the fluid and to evidence the contribution of an excitonic reservoir. We report on the generation of collective excitations at negative energies, on the ghost branch of the dispersion curve. Precursors of dynamical instabilities are also identified. Our methods open the way to the precise study of quantum hydrodynamics of quantum fluids of light.

Vacuum quantum fluctuations near horizons are known to yield correlated emission by the Hawking effect. We use a driven-dissipative quantum fluid of microcavity polaritons as an analog model of a quantum field theory on a black-hole spacetime and numerically calculate correlated emission. We show that, in addition to the Hawking effect at the sonic horizon, quantum fluctuations may result in a sizable stationary excitation of a quasinormal mode of the field theory. Observable signatures of the excitation of the quasinormal mode are found in the spatial density fluctuations as well as in the spectrum of Hawking emission. This suggests an intrinsic fluctuation-driven mechanism leading to the quantum excitation of quasinormal modes on black hole spacetimes.

M. J. Jacquet1∗†, M. Joly1∗, F. Claude, L. Giacomelli, E. Giacobino, Q. Glorieux, I. Carusotto, and A. Bramati 1 Laboratoire Kastler Brossel, Sorbonne Université, CNRS, ENS-Université PSL, Collège de France, Paris 75005, France 2 INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, via Sommarive 14, I-38050 Povo, Trento, Italy ∗ These two authors contributed equally to the work. † correspondance to maxime.jacquet@lkb.upmc.fr

Hot atomic vapors are widely used in non-linear and quantum optics due to their large Kerr non-linearity. While the linear refractive index and the transmission are precisely measured and well modeled theoretically, similar characterization remains partial for the $\chi^{(3)}$ non-linear part of the susceptibility. In this work, we present a set of tools to measure and estimate numerically the non-linear index of hot atomic vapors both in the steady state and during the transient response of the medium. We apply these techniques for the characterization of a hot vapor of rubidium and we evidence the critical role played by transit effects, due to finite beam sizes, in the measurement of the non-linear index.