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DTSTART;TZID=Europe/Paris:20260505T110000
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UID:12229-1777978800-1777984200@fermi.univ-tlse3.fr
SUMMARY:An optical lattice clock with a bosonic isotope of mercury. - (Ashley BEGUIN / LCAR / Seminar). - 5/05/2026\, 11H
DESCRIPTION:Séminaire LCAR \nAshley BEGUIN\, LTE\, Observatoire de Paris\, Université PSL\, Sorbonne Université\, Université de Lille\, LNE \nSummary\nSince 1967\, time has been defined through atomic transition frequencies\, establishing atomic clocks as fundamental tools for science and technology. More recently\, optical atomic clocks have surpassed historical atomic microwave clocks\, reaching uncertainties close to 10⁻¹⁸ and enabling both applied and fundamental investigations. At this level of performance\, atomic clocks serve as sensitive probes for a wide range of applications\, such as chronometric geodesy\, tests of General Relativity\, searches for physics beyond the Standard Model\, and the prospective redefinition of the SI second [1]. In addition\, frequency ratio measurements would provide powerful tools to constrain possible variations of fundamental constants\, such as the fine-structure constant α and the proton-to-electron mass ratio [2]. \nAmong neutral atoms\, mercury offers several attractive features for an optical lattice clock\, including a low sensitivity to blackbody radiation—16 times lower than ytterbium and 30 times lower than strontium—and a relatively high vapor pressure at room temperature. To date\, only the fermionic isotope ¹⁹⁹Hg has been used in mercury clocks. However\, the limited lifetime of its excited state constrains the performance achievable with the next generation of ultrastable lasers. In contrast\, bosonic isotopes offer a way to overcome this limitation\, as they allow for much longer interrogation times\, with the normally forbidden ¹S₀–³P₀ transition made accessible through a quenching scheme using a strong external magnetic field [3]. \nHere\, we present the first ¹⁹⁸Hg optical lattice clock and its comparison with a local state-of-the-art ⁸⁷Sr optical lattice clock. This clock is estimated to operate with a relative frequency stability already as low as 6 × 10⁻¹⁶/√(τ/s)\, and the 198Hg/87Sr optical frequency ratio could be determined for the first time with a preliminary total relative systematic uncertainty of 6.9 × 10⁻¹⁶ [4]. With this magnetically induced transition\, both the quadratic Zeeman shift (QZS) and the probe light shift (PLS) play indeed a significant role in the total uncertainty budget. Careful calibration and optimized experimental conditions can reduce the QZS uncertainty below the 10⁻¹⁷ level\, whereas the PLS remains a major limitation under our current experimental setup. We are now working on implementing hyper-Ramsey interrogation [5] to suppress the PLS uncertainty to lower levels. Future steps will focus on further improving the clock stability by employing repumping techniques for normalized detection and achieving lower atomic temperatures through a sideband cooling scheme. \n\n[1] W. F. McGrew et al\, Nature\, 564\, 87 (2018). A. D. Ludlow et al\, Rev. Mod. Phys.\, 87\, 637 (2015). S. Bize\, Comptes Rendus Physique\, 20\, 153 (2019).\n[2] Uzan J.P.\, Living Rev. Relativ. 14 (2011) 2.\n[3] A. V. Taichenachev et al\, Phys. Rev. Lett.\, 96\, 083001 (2006).\n[4] C. Zyskind\, et al.\, arXiv:2512.04920 (2025).\n[5] V. I. Yudin\, et al.\, Phys. Rev. A 82\, 011804(R) (2010).
URL:https://fermi.univ-tlse3.fr/event/an-optical-lattice-clock-with-a-bosonic-isotope-of-mercury-ashley-beguin-lcar-seminar-5-05-2026-11h/
LOCATION:Salle de conférence\, Bâtiment 3R4
CATEGORIES:Events,LCAR,Seminars
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DTSTART;TZID=Europe/Paris:20260505T140000
DTEND;TZID=Europe/Paris:20260505T153000
DTSTAMP:20260504T072414Z
CREATED:20260504T075434Z
LAST-MODIFIED:20260504T072414Z
UID:12085-1777989600-1777995000@fermi.univ-tlse3.fr
SUMMARY:Comment la géométrie et la topologie rendent les matériaux rigides… ou étonnamment souples. - (Christian D Santangelo / LPT / Seminar). -5/05/2026\, 14H
DESCRIPTION:Séminaire LPT \nChristian D Santangelo (Université de Syracuse) \nSeminar LPT\, 5/05/2026\, 14H\, 3R4\, salle de conférence\n\nSummary\nThe materials of biology\, from sharkskin to cartilage to wood\, regularly out-perform their synthetic equivalents. Organisms can achieve this because their materials have precise geometric structures that endow them with tailored mechanical properties that can often be changed in situ. It has recently become possible to fabricate comparable structures\, but we still seem to understand little about how geometry and mechanics are intertwined. \nThis talk will discuss why this is a hard problem (NP-hard actually)\, and highlight new work by my group and collaborators that are starting to unveil new connections between geometry and mechanics. This new understanding has allowed us to design materials that can change their mechanical properties\, changing from rigid to floppy due to the imposition of internal stresses.
URL:https://fermi.univ-tlse3.fr/event/tba-christian-d-santangelo-lpt-seminar-5-05-2026-14h/
LOCATION:Salle de conférence\, Bâtiment 3R4
CATEGORIES:Events,LPT,Seminars
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