“…We also note that alternative strategies are promising: the reader will find a recent review of sympathetic cooling of molecular ions by ultra-cold neutral atoms in (65 ). 12 Precise spectroscopic measurements with molecules have indeed increasingly been used in the last decade to test fundamental symmetries (parity (66 , 67 ), or parity and time-reversal, a signature of which would be the existence of a non-zero electron EDM, see note 1 ) and postulates of quantum mechanics (68 ), to measure either absolute values of fundamental constants (such as the Boltzmann constant k B (69 , 70 ), or the protonto-electron mass ratio µ, with recently the first determination of µ from a molecular system (71 )), or their variation in time (fine structure constant α (72 ), proton-to-electron mass ratio µ, see note 2 ) 13 Over the last few years, several techniques for the production of molecular ions have emerged and are reviewed in (65 ). The technique pioneered by the Drewsen group consists in first trapping an atomic ion of interest, usually produced by ionization of a neutral atomic gas, and then leaking in neutral molecular gas to react with the atomic ions and produce the desired molecular ions (22 ).…”