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    Rebound effects, LEDs and the role of technology in the ecological transition

    C2N amphitheater, ,

    Bruno GAYRAL

    CEA-Grenoble / IRIG / PHELIQS / NPSC, , Grenoble


    The citation for the 2014 Nobel Prize in Physics was for “the invention of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources”, thus suggesting that visible LEDs for lighting lead to global energy savings. As is well known among economists (but perhaps less among physicists, engineers and policy makers), the various rebound effects can severely affect the overall energy-consumption gain (if any) when a more energy-efficient technology comes to market. It is an open question to assess whether the III-N LED technology actually leads to energy savings.
    I will discuss the notion of rebound effect (notably direct and indirect rebound effects) in general and then for the case of the III-N LED technology, notably in light of the surprisingly scarce literature on the topic. I will then discuss the forecasted rise of the micro-display market for virtual-reality and augmented-reality applications (arguably much less of a basic need for humanity than lighting), which is based on the same technology as LEDs for lighting. In this sense, III-N LEDs illustrate quite well that it is not possible to claim a priori that a technological innovation will lead to energy savings. I will conclude by discussing what I think this implies for the ethics of scientific communication.

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    Les merveilleux nuages; que faire du nucléaire ?

    C2N amphitheater, ,

    Harry Bernas

    CNRS-Université Paris-Saclay, ,


    C’est d’abord la structure sociale et économique qui détermine la manière d’utiliser l’énergie. Or les sociétés changeront profondément dans les trois décennies à venir sous la pression des changements du climat et du vivant. Le projet annoncé de “nouveau nucléaire” en France contribuerait-il à une adaptation soutenable de la société à ces transformations, d’ici 2050 ? Ce devra(it) être le sujet d’un débat public, informé et démocratique. On propose un bref examen de l’histoire et de la faisabilité industrielle, économique et sociale du nucléaire face aux urgences imposées par les changements planétaires.

    Harry Bernas est physicien (nanosciences, matériaux irradiés). Il a dirigé le Centre de sciences nucléaires et de sciences de la matière (CNRS-Université Paris-Saclay). Récemment il a publié, outre des travaux en matière d’histoire contemporaine des sciences et des rapports sciences-technologie-société, un ouvrage, L’Île au bonheur (éd. Le Pommier, 2022). Ce séminaire est issu de son dernier livre (éd. Seuil, sept. 2023)

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    (en anglais) First C2N Colloquium 2024 - Quantum dots : a journey from solid-state physics to quantum technologies

    C2N - Université Paris-Saclay, Amphitheater, Palaiseau

    Pascale Senellart

    CNRS-Centre de Nanosciences et de Nanotechnologies, C2N, Palaiseau


    Semiconductor quantum dots have emerged as interesting quantum emitters for quantum technologies. First synthetized in the laboratories of France Telecom in the mid 80s, their quantum properties have been unraveled in 1994 by Jean-Yves Marzin and Jean-Michel Gérard [1]. Progressively, quantum dots have been shown to behave as artificial atoms, combining the great potential for quantum optics of natural atoms, with unique features arising from their solid-state environment.

    In this talk, I will discuss how our team at C2N contributed to this journey from solid-state nanophotonics to quantum technologies. I will fist explain how we have progressively developed efficient sources of single and entangled photons  [2] that are now commercialized by the C2N spin-off Quandela. These devices allow implementing small-scale quantum computing protocols with 6 photons [3]. To scale-up, we recently reached an important milestone where multiple photons are entangled with a single spin [4]. Finally, I will illustrate how the maturity of our devices now allow us to go back to fundamental studies such as revisiting the process of spontaneous emission [5,6] or studying energetic exchanges in the quantum realm [7].

    [1] J. -Y. Marzin, et al.,  Phys. Rev. Lett. 73, 716 (1994)

    [2] N. Somaschi, V. Giesz et al, Nature Photonics 10, 340-345,  (2016)

    [3] N. Maring et al.,  arXiv:2306.00874

    [4] N. Coste et al., Nature Photonics (2023)

    [5] J. Loredo et al, Nature Photonics 13, 803 (2019)

    [6] S. Wein et al, Nature Photonics 16, 374 (2022)

    [7] I. Maillette de Buy Wenniger, Physical Review Letter (2023)

    Keywords: quantum dots, microcavities, single photons, quantum computing


    Graduated from École Polytechnique and Doctor in Quantum Physics from Université Paris 6, Pascale Senellart joined the CNRS in 2001. She was appointed senior researcher in 2011 and associate professor at Polytechnique in 2014. Her research activity is at the interface between nanosciences, semiconductor physics and quantum optics. She received the CNRS Silver Medal in 2014, the Prix Mergier-Bourdeix in 2021, the Prix Jean Ricard in 2023 and was elected at the French Science Academy in 2022. She is  co-founder and scientific advisor of the C2N spin-off Quandela who develops solutions for optical quantum computing.

    Welcome at 9:30 am with a coffee - croissant time