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Quantum cryptography integrating an optical quantum memory
No full textInternational audienceDevelopments in scalable quantum networks rely critically on optical quantum memories, which are key components enabling the storage of quantum information. These memories play a pivotal role for entanglement distribution and long-distance quantum communication, with remarkable advances achieved in this context. However, optical memories have broader applications, and their storage and buffering capabilities can benefit a wide range of future quantum technologies. Here we present the first demonstration of a cryptography protocol incorporating an intermediate quantum memory layer. Specifically, we implement Wiesner's unforgeable quantum money primitive with a storage step, rather than as an on-the-fly procedure. This protocol imposes stringent requirements on storage efficiency and noise level to reach a secure regime. We demonstrate the implementation with polarization encoding of weak coherent states of light and a high-efficiency cold-atom-based quantum memory, and validate the full scheme. Our results showcase a major capability, opening new avenues for quantum memory utilization and network functionalities
Unveiling the kinematics of a central region in the triple-AGN host NGC 7733-7734 interacting group
No full textInternational audienceWe present a detailed study of the interacting triple active galactic nuclear system, NGC 7733-34, focusing on stellar kinematics, ionised gas characteristics, and star formation within the central region and stellar bars of both galaxies. We performed a comprehensive analysis using archival data from MUSE, HST/ACS, and DECaLS, complemented with observations from UVIT and IRSF. We identified a disc-like bulge in both NGC 7733 and NGC 7734 through a 2D decomposition. A central nuclear structure, with a semi-major axis of ∼1.113 kpc, was detected in NGC 7733 via a photometric and kinematic analysis, confirmed by the strong anti-correlation between V / σ and h 3 , indicative of circular orbits in the centre. NGC 7734 lacks a distinct nuclear structure. The presence of a disc-like bulge results in an anti-correlation between V / σ and h 3 , along with diffuse light. However, it does show higher central velocity dispersion, possibly attributed to an interaction with a smaller clump, which is likely a fourth galaxy within the system. Both galaxies demonstrate ongoing star formation, evidenced by FUV and H α observations. NGC 7734 shows recent star formation along its bar, while NGC 7733 experiences bar quenching. The star formation rate (SFR) analysis of NGC 7734 reveals that the bar region’s SFR dominates the galaxy’s overall SFR. Conversely, in NGC 7733, the lack of star formation along the bar and the presence of a Seyfert 2 active galactic nucleus (AGN) at the galaxy centre suggest the possibility of link among both. However, this would not affect the galaxy’s overall star formation. Our findings provide valuable insights into the stellar and gas kinematics, star formation processes, and AGN feedback mechanisms in interacting galaxies hosting stellar bars
Mapping and modeling the semantic space of math concepts
No full textMathematics is an underexplored domain of human cognition. While many studies have focused on subsets of math concepts such as numbers, fractions, or geometric shapes, few have ventured beyond these elementary domains. Here, we attempted to map out the full space of math concepts and to answer two specific questions: can distributed semantic models, such a GloVe, provide a satisfactory fit to human semantic judgments in mathematics? And how does this fit vary with education? We first analyzed all of the French and English Wikipedia pages with math contents, and used a semi-automatic procedure to extract the 1,000 most frequent math terms in both languages. In a second step, we collected extensive behavioral judgments of familiarity and semantic similarity between them. About half of the variance in human similarity judgments was explained by vector embeddings that attempt to capture latent semantic structures based on cooccurence statistics. Participants’ self-reported level of education modulated familiarity and similarity, allowing us to create a partial hierarchy among high-level math concepts. Our results converge onto the proposal of a map of math space, organized as a database of math terms with information about their frequency, familiarity, grade of acquisition, and entanglement with other concepts
Extending Si/C Anode Longevity through the Electrode Structure and Composition Design for All-Solid-State Batteries
No full textInternational audienceNumerous volume changes and sluggish kinetics causing irreversible Li-trapping and, consequently, a dramatic capacity decline during cycling are the main challenges facing Si-based anodes in all-solid-state batteries (ASSBs). The incorporation of carbon and Si significantly combats volume change and enhances electronic transport but cannot eliminate Li-trapping. Herein, we partially solve this issue by adding Li3.75Si alloy into a Si/C composite as a Li reservoir by making either a bilayer electrode or a blended electrode. We demonstrate that the bilayer electrode has superior cycling performance but suffers from soft shorting problems at high current density. This contrasts with the blended electrode, which exhibits a three-fold higher electrode critical current density (CCD), as captured from a self-designed three-electrode cell, but with limited cycling performance. In addition, we present the positive effect of adding a solid electrolyte (SE) to the blended electrode and show that ASSBs having Ni-rich cathodes and SE-containing blended negative electrode can achieve 500 stable cycles at 0.8 mA/cm2 and 183 cycles at 3 mA/cm2 due to the enhanced ionic/electronic percolations. Altogether, these results provide further insights into achieving long-lifespan, high-rate, and dendrite-free Si-based ASSBs through regulation of the electrode structure and composition
The genealogy of a political concept 'Refugee' or the Europeanization of the world system
No full textInternational audienceWhy do we speak about refugees or migrant? Following up an investigation around the use of the notion, this chapter shows how qualifying somebody as a refugee meant recognizing his or her community as potential people, that a autonomous body politics. This qualification depends on sectarian and racial criteria
Probing the magnetic origin of the pseudogap using a Fermi-Hubbard quantum simulator
No full textInternational audienceIn strongly correlated materials, interacting electrons are entangled and form collective quantum states, resulting in rich low-temperature phase diagrams. Notable examples include cuprate superconductors, in which superconductivity emerges at low doping out of an unusual ``pseudogap'' metallic state above the critical temperature. The Fermi-Hubbard model, describing a wide range of phenomena associated with strong electron correlations, still offers major computational challenges despite its simple formulation. In this context, ultracold atoms quantum simulators have provided invaluable insights into the microscopic nature of correlated quantum states. Here, we use a quantum gas microscope Fermi-Hubbard simulator to explore a wide range of doping levels and temperatures in a regime where a pseudogap is known to develop. By measuring multi-point correlation functions up to fifth order, we uncover a novel universal behaviour in magnetic and higher-order spin-charge correlations. This behaviour is characterized by a doping-dependent energy scale that governs the exponential growth of the magnetic correlation length upon cooling. Accurate comparisons with determinant Quantum Monte Carlo and Minimally Entangled Typical Thermal States simulations confirm that this energy scale agrees well with the pseudogap temperature . Our findings establish a qualitative and quantitative understanding of the magnetic origin and physical nature of the pseudogap and pave the way towards the exploration of pairing and collective phenomena among charge carriers expected to emerge at lower temperatures
Rapid shifts in an alpine lake ecosystem of the Southern Alps in response to Late Glacial-Holocene centennial-scale events inferred from diatom assemblages
No full textInternational audienceAlpine lakes in the Mediterranean region are experiencing rapid warming, posing a threat to aquatic ecosystem diversity and functioning. Documenting how high-altitude lake ecosystems have responded to past warming and cooling events is of interest to scale modern changes in a long-term context, and to inform management strategies. This paleoenvironmental study focuses on Lake Petit (2200 m a.s.l., Southern Alps) and combines the analysis of subfossil diatoms and inorganic and organic sediment composition over the last 14,000 years. The results show a major ecosystem shift at the Late Glacial-Holocene transition, ca. 12,000 years ago. In addition, the alternating dominance of diatoms from the Fragilariaceae (e.g., Pseudostaurosira pseudoconstruens, Staurosira venter) and Gomphonemaceae (e.g., Gomphonema elegantissimum), along with high-amplitude fluctuations in biogenic silica concentrations, highlight rapid ecological shifts at four distinct periods: 10,100–9800, 9200–9000, 8100–8000, and 7000–6900 cal yr BP. These shifts reveal the occurrence of four centennial-scale cooling events at the beginning of the Holocene. During the warmer Middle-Holocene period, diatom assemblages are dominated by Staurosirella neopinnata, ending with a shift coinciding with the 4.2 ka climate event, described in a previous study. A progressive return of S. neopinnata is observed nowadays. Our findings suggest that during the Early Holocene, the lake ecosystem was capable of buffering centennial-scale cooling events, consistently returning to previous conditions. However, the two phases of major long-lasting ecological shift that occurred 7000 and 4200 years ago, likely driven by catchment-related factors such as pedogenesis and vegetation dynamics, led to stepwise changes in ecosystem functioning baselines. This paper raises once again questions about the capacity of modern aquatic high-altitude lake ecosytems to recover from ongoing climate change when local baselines are no longer in equilibrium with natural variability