The group Metrology, Molecules and Fundamental Tests is performing ultra-high resolution molecular spectroscopy in the near and middle infrared and optical frequency metrology. The main experimental projects are the following:
Measuring parity violation effects in cold chiral molecules
Benoît Darquié, Olivier Lopez, Anne Amy-Klein, Christophe Daussy, Christian Chardonnet, Matthieu Pierens (PhD), Dang Bao An Tran (PhD), Louis Lecordier (PhD), Mathieu Manceau (postdoc), Anne Cournol (postdoc)
Visitor: Alexander Shelkovnikov (Lebedev Physics Institute, Moscow)
Former member: Sean Tokunaga (lecturer)
We are developing a new-generation molecular clock specifically designed for precision vibrational spectroscopy of complex polyatomic molecules in the gas phase. The proposed technology is at the forefront of cold molecule research and frequency metrology, and opens possibilities for using polyatomic molecules to perform tests of fundamental physics and explore the limits of the standard model. The apparatus will be used in the first place for the measurement of the tiny energy difference between enantiomers of a chiral molecule induced by electroweak interactions, a signature of parity (left-right symmetry) violation, which has yet to be observed. Our efforts towards making this measurement have been described as a 'frontier experiment' by Naturea. Confirming this prediction is important for several reasons. It is a probe of the weak interaction and would thus serve as a test of the standard model. But it will also shed light on the origin of biomolecular homochirality, the unexplained but possibly related puzzle that Nature works only with L-amino acids and D-sugars, not their mirror images.
We are thus constructing a molecular beam Ramsey interferometer using ultra-narrow mid-infrared lasers calibrated against primary frequency standards (taking advantage of our work on frequency dissemination by optical fibre links). We will then be able to measure absolute frequencies to 1 part in 1014 and parity violation frequency shifts to better than 1 part in 1015 . Besides, our chemist collaborators can now provide samples of species which, although in the solid phase, have potentially measurable parity violation frequency shifts of a few 10-14 .
We have conducted preliminary investigations on methyltrioxorhenium (MTO), the achiral parent of the ideal candidate species. This include Doppler and sub-Doppler spectroscopy in room temperature and cryogenic cells, and in supersonic beams. We have used our data in a combined analysis of microwave, millimetre wave and infrared measurements, to build an accurate spectroscopic model of this complex and heavy molecule, accounting for the hyperfine structure [3,4].
Buffer gas-cooled beams can provide the low temperature, low speed, and high intensity needed to maximise resolution and statistical precision. In collaboration with Imperial College London, we have demonstrated buffer-gas cooling of the first organometallic species, MTO, extending buffer-gas cooling to a new class of molecules of interest for parity violation measurements .
We have also started to replace our long-standing frequency-stabilised CO2 lasers by quantum cascade lasers (QCLs). Using QCLs gives access to the entire mid-infrared region, leading to a considerable increase in potential candidate species. We have phase-locked a QCL to an ultra-stable CO2 laser and transferred the excellent spectral purity of the CO2 laser to the QCL . We have also developed a method to lock any mid-infrared radiation to a frequency comb referenced to the primary frequency standards of the French national metrology institute, resulting in record stabilities and accuracies  (more more details here, also advertised in Physics Todayb).
a N Jones, Tough Science – Five experiments as hard as finding the Higgs, Nature 481, 14 (2012)
b JL Miller, Precision spectroscopy comes to the mid-IR, Phys. Today 68(8) 16 (2015)
Figure: Because of weak nuclear interactions, right and left enantiomers of a chiral molecule are not mirror images.
Agence Nationale de la Recherche (ANR), Région Île-de-France via Domaine d’Intérêt Majeur - Des atomes froids aux nanosciences (DIM-NanoK)
- S. K. Tokunaga, C. Stoeffler, F. Auguste, A. Shelkovnikov, C. Daussy, A. Amy-Klein, C. Chardonnet and B. Darquié,
Probing weak force induced parity violation by high resolution mid-infrared molecular spectroscopy,
Mol. Phys. 111, 2363-2373 (2013); arXiv
- N Saleh, R Bast, N Vanthuyne, C Roussel, T Saue, B Darquié and J. Crassous,
An oxorhenium complex bearing a chiral cyclohexane-1-olato-2-thiolato ligand: synthesis, stereochemistry and theoretical study of parity violation vibrational frequency shifts,
Chirality, in press (2017).
- P Asselin, Y Berger, TR Huet, L Margulès, R Motiyenko, RJ Hendricks, MR Tarbutt, SK Tokunaga and B Darquié,
Characterising molecules for fundamental physics: an accurate spectroscopic model of methyltrioxorhenium derived from new infrared and millimetre-wave measurements,
Phys. Chem. Chem. Phys. 19, 4576-4587 (2017); arXiv
- SK Tokunaga, RJ Hendricks, MR Tarbutt and B Darquié,
High-resolution mid-infrared spectroscopy of buffer-gas-cooled methyltrioxorhenium molecules,
New J. Phys. 19, 053006 (2017); arXiv
- PLT Sow, S Mejri, SK Tokunaga, O Lopez, A Goncharov, B Argence, C Chardonnet, A Amy-Klein, C Daussy and B Darquié,
A widely tunable 10-µm quantum cascade laser phase-locked to a state-of-the-art mid-infrared reference for precision molecular spectroscopy,
App. Phys. Lett. 104, 264101 (2014); arXiv
- B Argence, B Chanteau, O Lopez, D Nicolodi, M Abgrall, C Chardonnet, C Daussy, B Darquié, Y Le Coq and A Amy-Klein,
Quantum cascade laser frequency stabilization at the sub-Hz level,
Nature Photon. 9, 456–460 (2015); arXiv