Ultracold Atom News

Research project The Trapped Ions team is developing an experimental setup aiming at performing a direct optical determination of the proton to electron mass ratio at the 0.01 ppb level through Doppler free two-photon vibrational spectroscopy in H2+ molecular ions. Spectroscopy will be performed by Resonance Enhanced Multiphoton Ionisation (2+1 REMPD) on state selected ions [1,2,3,4]. The H2+ ions are confined in a linear Paul trap and sympathetically cooled by laser cooled Be+ ions. The H2+ ions are created by Resonance Enhanced Multiphoton Ionisation (REMPI) at 303 nm. The H2+ spectroscopy laser is an utrastable quantum cascade laser (QCL) phase-locked on a CO2 laser matched to a Fabry-Perot cavity surrounding the ion cloud. The work of the post doctoral scientist will first consist in characterising the temperature and the ro-vibrational populations of the state selected H2+ ion sample. It will then consist in achieving the first observation of the (v=0,L=2) → (v=1,L=2) two-photon transition in H2+ towards a mp/me determination by comparison with highly accurate calculations. [1] Jean-Philippe Karr, Franck Bielsa, Albane Douillet, Jofre Pedregosa, Vladimir I. Korobov, Laurent Hilico, Phys. Rev. A 77, 063410 (2008). Vibrational spectroscopy of H2+: Hyperfine structure of two-photon transitions. [2] Jean-Philippe Karr, Albane Douillet, Laurent Hilico, Applied Physics B 107, 1043-1052 (2012). DOI 10.1007/s00340-011-4757-z (2011). Photodissociation of trapped H2+ for REMPD spectroscopy. [3] Biesheuvel, J.-Ph. Karr, L. Hilico, K.S.E. Eikema, W. Ubachs, J.C.J. Koelemeij, Nature Communications 7, 10385 (2016). Probing QED and fundamental constants through laser spectroscopy of vibrational transitions in HD+ [4] V.I. Korobov, J.C.J. Koelemeij, L. Hilico, J.-Ph. Karr, Phys. Rev. Lett. 116, 053003 (2016). Theoretical Hyperfine Structure of the Molecular Hydrogen Ion at the 1 ppm Level