Quantum coherence, central to modern physics, underlies phenomena such as entanglement and Rabi oscillations, which lack classical analogues. This internship aims to explore a fundamental open question: can a relativistic free electron be entangled with a photon through its interaction with a plasmon? The project, which may evolve into a PhD thesis, combines experimental, instrumental, and theoretical efforts to reveal temporal correlations between ~100 keV electrons and photons mediated by surface plasmons. Using a scanning transmission electron microscope, a nanoscale electron probe will be positioned with nanometric precision on specially designed chiral plasmonic structures that emit circularly polarized photons at specific plasmonic resonances. Preliminary calculations indicate that in these conditions, each inelastic electron acquires a defined orbital angular momentum and becomes nearly perfectly entangled with a circularly polarized photon. The internship will focus on performing correlation measurements between electrons and photons to probe this entanglement, including tests of Bell inequality violations. These experiments will leverage a unique combination of advanced instrumentation, tailored nanostructures, and state-of-the-art detectors available in our group.

Nano-optics explores optical phenomena occurring far below the diffraction limit of light. To overcome this limit, new concepts and techniques have emerged, among which the use of fast electrons—traveling at about half the speed of light—has proven uniquely powerful for probing the optical properties of nanomaterials. Our team has been a pioneer in this field, using electron energy-loss spectroscopy (EELS) and cathodoluminescence (CL) to study a wide range of excitations in solids, from phonons to excitons, with unprecedented spatial and spectral resolution. More recently, we have developed energy-gain spectroscopy (EEGS), which combines the picometer-scale spatial precision of fast electrons with the sub-µeV spectral resolution of a laser. This innovation enables the investigation of quantum-optical systems such as ultra-high-finesse optical cavities. However, a key question remains open: can we coherently study and manipulate optical states in atomic or quasi-atomic systems such as quantum dots using relativistic electrons? The aim of this internship, potentially leading to a PhD, is to explore this new regime of coherent control of artificial atoms with electron beams. The project will take place on a unique platform coupling a monochromated transmission electron microscope with a laser system and custom-designed lithographic samples, opening unprecedented perspectives in quantum nano-optics.

The 2D+ Research Group at CRHEA, located on the French Riviera near Nice, France, is seeking a highly motivated and talented master candidate to join our cutting-edge research in nanophotonics with 2D materials. We offer a unique opportunity to explore emerging phenomena such as sliding ferroelectricity, ultra-low-threshold nonlinear photonics, and exciton engineering. The project is part of the European-funded 2DFERROPLEX consortium, bringing together leading experts in the field.

The topic of the internship is to probe chains of semiconductor nanoplatelets by fluorescence microscopy and examine whether these structures exhibit superfluorescence, a mechanism by which incoherently excited dipoles, because of their coupling to the electromagnetic field, spontaneously develop a coherence and interfere constructively, leading to accelerated emission and original properties for emission correlations and directionality.

Chaotic systems have a particular quantum behavior and several conjectures remain to be demonstrated concerning their spectrum and their wave functions [1]. Graphs can be chaotic or not and allow a relatively simple theoretical study of the classical and quantum limits [2]. These experiments are easier to carry out in photonics and the formalism fits well to the wave-particle duality of light. We have therefore produced graphs (chaotic or not) where light circulates in silicon waveguides (Fig. 1a) and we study their spectrum (Fig. 1c) and their wave functions (Fig. 1b). The first objective is to verify the validity of the conjectures according to different types of graphs. In a second step, we will inject non-classical light (squeezed light or entangled photons for instance) to know if entanglement is sensitive to chaos. The silicon graphs are fabricated in the C2N cleanroom. Their design requires numerical simulations performed under the supervision of Xavier Chécoury (C2N). The experiments are carried out on a dedicated characterization setup at C2N and the theory is developed in collaboration with Barbara Dietz (Dresden). The student may be involved in one or several of these tasks, depending on his/her preferences.

The master’s student will join Laboratoire de Physique des Lasers (LPL) to develop a compact microwave (MW) spectrometer operating from 2–20 GHz. This instrument is designed both as a sensitive detector of internal quantum states in polyatomic molecules and as a precision tool for molecular frequency metrology. Proof-of-principle measurements have already shown free induction decay signals on the OCS J = 0 → 1 transition at 12.163 GHz with excellent signal-to-noise ratios. The next objective is sub-Hz accuracy, made possible by ultrastable, SI-traceable frequency references distributed by the REFIMEVE network. Within the ANR Ultiμos project, the spectrometer will enable cross-checks between MW rotational frequencies and mid-infrared (MIR) rovibrational data measured at the 100 Hz level. These comparisons are motivated by the search for variations of the proton-to-electron mass ratio μ, a key constant of the Standard Model. Methanol and ammonia, with transitions highly sensitive to μ, are particularly powerful probes. MIR and MW results, obtained via independent experimental chains, will provide robust cross-validation of frequencies and uncertainty budgets. The student will contribute to optimizing waveguide and cavity configurations, performing precision spectroscopy on benchmark species, developing MIR–MW double-resonance schemes to enhance sensitivity, and preparing integration with a cryogenic buffer-gas cooling source (~3 K).

The master’s student will contribute to the development of a new-generation molecular clock dedicated to precision vibrational spectroscopy of cold molecules in the gas phase. This cutting-edge platform combines cold molecule research and frequency metrology, enabling fundamental tests of physics beyond the Standard Model. A key first objective is the measurement of the tiny electroweak-induced energy difference between enantiomers of a chiral molecule—a direct signature of parity (left-right symmetry) violation and a sensitive probe of dark matter. Molecules, with their rich internal structure, offer unique opportunities compared to atoms for precision measurements. They are increasingly used to test fundamental symmetries, measure fundamental constants and their possible time variations, and search for dark matter. Such experiments rely on ultra-precise determination of molecular transition frequencies, requiring advanced techniques familiar in atomic physics: selective state control, high detection efficiency, long coherence times, and cooling of internal and external degrees of freedom. The student will play an active role in early developments of the experiment, including: setting up mid-infrared quantum cascade laser systems at 6.4 μm and 15.5 μm to probe molecular vibrations; and performing first Doppler and sub-Doppler absorption spectroscopy on cold molecules (~1 K) generated in a novel apparatus.

The master’s student will take part in forefront experiments dedicated to ultra-precise measurements of rovibrational molecular transitions to test a possible time variation of the proton-to-electron mass ratio (μ), a key constant of the Standard Model. Detecting such a drift would signal new physics and shed light on dark matter and dark energy. The approach relies on comparing astronomical molecular spectra with laboratory data. The experimental setup uses quantum cascade lasers (QCLs) stabilized to optical frequency combs traceable to primary standards, a technology pioneered at LPL that enables unprecedented precision in the mid-infrared. The internship centers on methanol (CH₃OH), whose transitions are especially sensitive to μ-variation. The student will install and stabilize a QCL in the relevant spectral region, aiming for sub-Doppler resolution and ~100 Hz frequency accuracy, necessary for astrophysical comparisons. This work is part of the ANR Ultiμos project with LKB and MONARIS, combining spectroscopy of methanol and other species such as ammonia to identify key transitions for Earth- and space-based campaigns. Partners including Vrije Universiteit Amsterdam and Onsala Space Observatory provide theory and astronomical input.

Research overview Materials can be studied using computer simulation which enables one to probe the motion of each constituent atoms and to build correlations between the macroscopic properties and the microscopic behaviors. On the one hand, traditional quantum mechanics methods provides particularly accurate results up to the electronic structure of the material. Yet, the drawback of this method concerns its computational cost which prevents from studying large system sizes and long time scales. On the other hand, effective potentials have been developed to mimic atomic interactions thereby reducing those issues. However, these potentials are often built to reproduce bulk properties of the materials and can hardly be employed to study some specific systems including interfaces and nanomaterials. In this context, a new class of interatomic potentials based on machine-learning algorithms is being developed to retain the accuracy of traditional quantum mechanics methods while being able to run simulations with larger system sizes and longer time scales. Simulation project Using computer simulations, the student will construct a database that should be representative of the different interactions occurring in a specific material. Machine-learning potentials based on the least-angle regression algorithm as well as neural network potentials will be trained and their accuracy will be studied as a function of the size and the complexity of the database.

Research overview The formation of a crystal is triggered by the emergence of a nucleation core. Classical nucleation theory (CNT) is widely employed to discuss its nature and its origin. In CNT, the thermodynamically stable phase is always the one that grows first and its size is then driven by the free energy competition between how much it costs to build a liquid-crystal interface and the gain from growing the crystal. Yet, following Ostwald’s rule, another structure may emerge beforehand if it is closer in free energy to the mother phase. Then, structural and also chemical reorganizations happen during the growth. This multi-stage nucleation mechanism already appears in bulk systems but can be amplified in nanocrystal nucleation where surface effects and chemical reactivity are enhanced. For nanoscience to be inspired by the practical applications instead of still being driven by the synthesis possibilities, it is crucial to reach a better understanding of the unique crystallization mechanisms leading to nanocrystals. Simulation project Atomistic simulations will be performed to study crystallization of binary particles. Examples will be taken from well-studied materials including CuZr, NiAl, NaCl, Water... We will investigate the correlation between the thermodynamic conditions and the final nanoparticles. The goal is to ultimately better understand how nucleation theory is affected by downsizing to the nanometric scale.

The frequency (or time-of-arrival) degree of freedom of a single photon represents a continuous variable used for encoding quantum information [1,2,3]. Frequency is less susceptible to noise in optical fibers, waveguides, and free space, making it a strong candidate for future quantum information processing. Unlike polarization, frequency is unaffected by birefringence, does not require phase stabilization, and is immune to nonlinear effects at the single-photon level. Given the high cost and impracticality of deploying new fiber infrastructure, the project explores how quantum communication can be integrated into existing classical networks by having the coexistence of quantum and classical signals within one optical fiber. This project investigates the development of a quantum channel mediated by stimulated Raman scattering (SRS), when there is coexistence of one classical field and a frequency-encoded single photon state. We will employ a light-matter interaction model to analyze how SRS-induced field distortion impacts the frequency encoding of single photons, including two-color and grid-state encodings [3]. The resulting spectral modifications will be quantified by their effect on quantum communication performance, specifically the quantum bit error rate (QBER) and the asymptotic key rate.

The project focuses on mixtures of electrons (fermion) and excitons (electron-hole pair, a boson) in a new class of materials: van der Waals heterostructures. The latter can be seen as a “mille-feuille”, obtained by stacking atomically thin sheets of various materials. They recently became a prominent platform to study many-body physics, after a milestone discovery of superconductivity in bilayer graphene. Our long term ambition is to introduce superconductivity in a controlled manner, using excitons as force-carrier bosons (instead of phonons in conventional superconductors). The internship will pave the way toward this goal. It includes two steps, (i) the fabrication of the heterostructures and (ii) a first characterization with optical spectroscopy.