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Cavity quantum electrodynamics with single perovskite quantum dots
No full textInternational audienceQuantum emitters of single indistinguishable photons play a key role in quantum technologies. Among condensed matter systems, colloidal perovskite quantum dots have emerged as promising candidates, exhibiting high-purity single photon emission at room temperature and two-photon interference visibilities up to 0.5 at cryogenic temperatures. Achieving deterministic coupling of individual perovskite quantum dots to photonic structures is now a critical step towards harnessing cavity quantum electrodynamics (cQED) effects, such as the Purcell effect, to enhance single photon emission rate and indistinguishability. Here, we demonstrate the deterministic and reversible coupling of individual CsPbBr perovskite quantum dots to a tunable, high-quality factor, low mode volume fiber-based Fabry-Pérot microcavity at 10~\si{\kelvin}. By spatially and spectrally tuning the cavity mode in resonance with the quantum dot emission, we observe up to a twofold increase in single photon emission rates. We build on the original multiplet excitonic fine structure to assess the vacuum Rabi coupling strength ( 40~\si{\micro eV}) from the shaping of the spectral profile of the emission upon increasing the electromagnetic confinement. This approach also made it possible to delineate the contributions of spectral diffusion and pure dephasing to the total linewidth of emission, paving the way to a fully optimized control of the emission properties of cavity coupled perovskite quantum dots
Optimal Moment-based Characterization of a Gaussian State
No full textInternational audienceFast and precise characterization of Gaussian states is crucial for their effective use in quantum technologies. In this work, we apply a multi-parameter moment-based estimation method that enables rapid and accurate determination of squeezing, antisqueezing, and the squeezing angle of the squeezed vacuum state. Compared to conventional approaches, our method achieves faster parameter estimation with reduced uncertainty, reaching the Cramér-Rao bound. We validate its effectiveness using the two most common measurement schemes in continuous-variable quantum optics: homodyne detection and double homodyne detection. This rapid estimation framework is well-suited for dynamically characterizing sources with time-dependent parameters, potentially enabling real-time feedback stabilization
Retour sur le mythe du Protagoras, entre anthropologie et philosophie
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Nucleus of M31: Upper limits to the molecular and ionised gas content
No full textInternational audienceWe report observations performed with the NOrthern Extended Millimeter Array (NOEMA) and Atacama Large Millimeter/submillimeter Array (ALMA) of the nucleus of Andromeda (M31) that place strong constraints on the presence of gas in the cold or warm phase. M31 hosts the largest supermassive black hole (SMBH) closer than 1 Mpc to us. Its nucleus is silent, with some murmurs at the level of 4 × 10−9LEdd, and it is surrounded by a disc of old stars with a radius of 5 pc. The mass loss from these stars is expected to fill a molecular gas disc within the tidal truncation of 1 pc ( = 0.26 arcsec) of 104 M⊙, corresponding to a CO(1–0) signal of 2 mJy with a line width of 1000 km/s. We observed the nucleus with NOEMA in CO(2–1) and with ALMA in CO(3–2) with angular resolutions of 0.5″(1.9 pc) and 0.12″(0.46 pc), respectively. We exclude the presence of molecular gas with an upper limit of 3σ on the H2 mass of 195 M⊙ based on CO(3–2) ALMA observations. The CO(3–2) upper limit also constrains warm gas, which escapes detection in CO(1–0). The scenario of cold gas accumulation next to the nucleus of M31 that originates from mass loss of the old stellar population is not verified and excluded at a level of 150σ. The hot gas expelled by the stellar winds might instead never cool or fall onto the disc. Alternatively, the mass-loss rate of the stellar wind may have been overestimated by a factor 50, and/or the ionised gas has escaped from the nucleus. The SMBH in M31 clearly is in a low activity state, similar to what is observed for Sgr A* in the Milky Way (MW). Recently, a cool (104 K) ionised accretion disc has been detected around Sgr A* in the H30α recombination line with ALMA. If the sizes, masses, and fluxes were rescaled according to the mass of the black hole of M31 (35 times higher than in the MW) and its distance (97 times further away than in the MW), a similar disc might easily be detectable around the nucleus of M31. The expected signal would be eight times weaker that the signal detected in SgrA*. We searched for an ionised gas disc around the nucleus of M31 with NOEMA, and we place a 3σ upper limit on the H30α recombination line at a level twice lower than expected with a simple scaling of the SgrA*
A comparative study of target fabrication strategies for microgram muonic atom spectroscopy
No full textInternational audienceMuonic atom spectroscopy is a method that can determine absolute nuclear charge radii with typical relative precision of . Recent developments have enabled to extend muonic atom spectroscopy to microscopic target quantities as low as 5\,{\upmu }\text {g}. This substantial reduction from the traditional limit of the order of is based on a transfer mechanism in a high-pressure hydrogen gas cell, which transports the muon to the surface of the target material rather than stopping it over a broad depth range. This approach enables the measurement of absolute nuclear charge radii of long-lived radioactive isotopes (half-life above 20 years), but the production of appropriate targets for the technique has presented some major challenges, such as the formation of organic layers on the substrate. This study presents a systematic investigation of the stopping efficiency for different target preparation methods: ion implantation, drop-on-demand printing, and molecular plating. Notable differences between the three methods were discovered in terms of their performance allowing to further fine tune the method of choice for future target preparations. Our findings show that implantation provides appropriate targets for our method with negligible losses. This achievement opens the landscape of potential measurements to isotopes where high mass separation is required not achievable with other methods. Furthermore, molecular plated targets performed substantially better than those prepared using drop-on-demand printing
Disruption of biological processes in the Anthropocene: the case of phenological mismatch
No full textInternational audienceBiologists are increasingly documenting anthropogenic disruptions, both at the organism and ecosystem levels, indicating that these disruptions are a fundamental, qualitative component of the Anthropocene. Nonetheless, the notion of disruption has yet to be theorized. Informally, disruptions are direct or indirect consequences of specific causes that impair the contribution of parts of living systems to their ability to last over time. To progress in this theorization, we work here on a particular case. Even relatively minor temperature changes can significantly impact plant-pollinator synchrony, disrupting mutualistic interaction networks. Understanding this phenomenon requires a specific rationale since models describing it use both historical and systemic reasoning. Specifically, history justifies that the ecosystem initially exists in a very narrow part of the possibility space where all its populations are viable, and the disruption leads to a more generic configuration where some populations are not viable. Building on this rationale, we develop a mathematical schema inspired by Boltzmann's entropy, apply it to this situation, and provide a technical definition of disruption
Bound–Free and Free–Free Pair Production Channels in Forward Delbrück Scattering
No full textInternational audienceWe present a theoretical study of forward-angle Delbrück scattering of light by the Coulomb field of a target nucleus. Special attention is paid to the Coulomb corrections, which take into account the interaction of the emerging virtual electron–positron pairs with the nucleus to higher orders of . We compare the results from three different computation methods: the direct all-order evaluation of the Delbrück amplitude, the computation from the pair production cross section with the optical theorem and the low-energy limit. We find that the values obtained from the optical theorem are in very good agreement with the all-order calculations and can be used as benchmark data. Moreover, both methods agree with the low-energy limit for photon energies when correctly accounting for the bound–free pair production cross section in the optical theorem calculations, and the discrepancy found in the literature originates from neglecting this contribution
