Title of seminar: Quantum logic control of molecular and transition-metal ions

Abstract:

Extending quantum control to increasingly complex systems is essential for advancing quantum technologies and probing fundamental physics. Molecules, in particular, serve as highly sensitive systems for detecting symmetry violations that may reveal physics beyond the Standard Model. However, their complex level structure makes quantum-state control challenging.

Quantum logic spectroscopy offers a promising path forward for molecular ions: a well-controlled atomic ion is co-trapped with a molecular ion and enables manipulation and readout of its quantum state via shared motional modes. I will present an overview of our latest results and concepts in quantum logic control of molecular ions. As we progress toward quantum logic spectroscopy of single molecular MgH⁺ ions, we are also assessing the broader applicability of these techniques to other ionic species. Recently, we demonstrated quantum logic control of a single titanium ion [1,2], showing that these methods can be extended to previously inaccessible atomic systems.

By enhancing control over new classes of ions, our work opens the door to novel applications in quantum technology and fundamental physics, making an extended range of species available for precision spectroscopy.

References:

[1] Rehmert et al. Quantum Logic Control of a Transition Metal Ion, Physical Review Letters 134, 113201 (2025)

[2] Rehmert et al. Landé g Factor Measurement of ⁴⁸Ti⁺ Using Simultaneous Comagnetometry and Quantum Logic Spectroscopy, Physical Review Letters 136, 083203 (2026)

Title of seminar: UV-Dual Comb Spectroscopy using a bidirectional mode-locked femtosecond Ti:Sapphire ring laser

Abstract :

The development of broadband, precise, and rapid molecular spectroscopy addresses current challenges in gas detection within dynamic and complex environments. I will present dual-comb spectroscopy, a technique that is particularly well suited to meeting these challenges. At the Institute of Light and Matter (Lyon), we are developing dual-comb spectroscopy in the UV spectral range to probe highly reactive species such as radicals. I will introduce the experimental dual-comb source we have developed, based on a mode-locked femtosecond Ti ring laser, discuss its unique characteristics and present spectroscopic results obtained in both the IR and UV spectral regions.

Title of seminar: Tests of fundamental physics using ytterbium ions

Abstract :

I will present the first results from my postdoc at PTB in Braunschweig, Germany. Trapped ions are widely used in optical clocks and fundamental physics. Among them, the forbidden electric octupole (E3) transition in 173Yb⁺ offers key advantages, including an extremely narrow natural linewidth and high sensitivity to physics beyond the Standard Model. The large electric quadrupole moment of its deformed nucleus is predicted to enhance this forbidden transition. I will show how we confirmed this effect and observed hyperfine-state-dependent quenching, paving the way toward multi-ion clocks using 173Yb⁺. I will further show how the rich hyperfine structure can be used to probe the nuclear properties of 173Yb⁺, making it a particularly promising candidate for searches of a fifth force using isotope shifts measurements and King plot analysis.

Title of seminar:  (Cold) Molecules as a tool to probe fundamental physics

Abstract:

Modern physics is struck with a paradox: there are very good reasons to believe that our current understanding of Nature is incomplete, yet it is exceedingly difficult to conduct an experiment which contradicts our best theories. This tension is particularly palpable since the Large Hadron Collider explored a wide range of energies without a clear detection of new physics, thereby discarding many extensions Beyond the Standard Model (BSM). Searching for new physics in the high energy domain now demands extremely large investments to build bigger and brighter instruments. Another approach, complementary but very powerful, is to perform small scale, low-energy experiments but with very high precision¹. In the last 20 years in particular, this led the community to look for new physics in much larger objects than elementary particle: molecules. Many proposals and experiments have demonstrated the potential of molecules to test our fundamental understanding of Nature: from probing variations of fundamental constants like the electron mass over the proton mass  or the fine-structure constant , or different models for dark matter, to testing the symmetrisation postulate of Quantum Mechanics or Bose-Einstein statistics. Especially notable are experiments currently responsible for the most stringent limit on the value of the electron electric dipole moment (which constraints strongly potential BSM theories).

However, the field is still in its infancy: the molecules that are currently used to explore new physics are composed of 2, 3 or 4 atoms at most, even though larger molecules offer qualitatively distinct opportunities in fundamental physics. The abundance of nearly degenerate rovibrational levels in the larger, polyatomic molecules (with more than 10 atoms) enhances their sensitivity to variations of fundamental constants or to potential ultralight bosonic dark matter. They can also provide a new system for implementing quantum computing, using either rotational or vibrational levels, and taking advantage of robust systematic error rejection schemes. Having more than 3 atoms also opens up the possibility to use molecular chirality to probe parity-violating interactions. Indeed, the energy levels of two enantiomers (the mirror-images of chiral molecules) are predicted to be slightly different, because of the parity-violation inherent to the weak interaction, or as a result of their interaction with dark-matter fields. Thus, a measurement of this symmetry-breaking energy difference ΔE_PV is a sensitive probe of the Standard Model and of physics BSM.

However, as the number of atoms in a molecule goes up, the number of energy levels increases very rapidly, as well as the couplings between these energy levels. These couplings limit the applicability of the usual cooling mechanisms because they induce population losses towards many different states. Couplings between different vibrational modes (denoted in the literature as Intramolecular Vibrational Redistribution (IVR)) also blur out spectroscopic resolution by what can be viewed as a loss of coherence due to non-radiative dynamic energy distribution in the molecule.

In this talk I will review the current use, the potential ahead and the obstacles on the way of using molecules for tests of fundamental physics, focussing on our on-going attempt to measure ΔE_PV in chiral molecules at the Laboratoire de Physique des Lasers.