Title: Frequency-comb-based spectroscopy of trapped and cold molecular ions

Key-words: Ion trapping and laser-cooling, cold molecular ions, spectroscopy, quantum state control, frequency-comb laser.

Supervisor: Cyrille SOLARO solaro@unistra.fr  

Location: European Center for Quantum Sciences – CESQ, ISIS, Université de Strasbourg, France

Contract: Fixed term, 36 months, starting in october 2024, funding already secured

Context: The ability to manipulate atoms and atomic ions at the most fundamental quantum level forms the basis for their application in modern quantum sciences. Achieving the same level of control over molecules would open up exciting new prospects in this field. However, the complex energy-level structure of molecular systems, which makes them so attractive, also poses serious difficulties for their translational cooling, as well as for the preparation, coherent manipulation and detection of their quantum states. In this context, hybrid systems composed of co-trapped atomic and molecular ions are very promising as they combine the high degree of control provided by the atomic ion with the rich energy-level structure of the molecular ion. This structure features numerous transitions with excellent coherence propertiesfor quantum information processing and precision measurements.

Description of the project: This PhD topic concerns the trapping and cooling of dipolar molecular ions (SrH+) as well as their spectroscopic characterization using a frequency-comb laser. The student will take part in the installation and development of the experimental apparatus and perform the first spectroscopic measurements of this molecular ion. SrH+ ions can be formed by photochemical reaction between trapped and laser-cooled Sr+ ions and molecular hydrogen. Via their Coulomb interaction with the remaining Sr+ ions, they can be “sympathetically” cooled and eventually become part of an ordered structure often referred to as a Coulomb crystal [1]. This situation is ideal for a first spectroscopic characterization of SrH+ which we will perform using state-selective resonance-enhanced photodissociation (REMPD) with a tunable femtosecond frequency-comb [2-4]. In a second step, we will refine this characterization via a 2-color REMPD scheme using a quantum cascade laser and the frequency-comb. We will also investigate non-destructive state-detection of the molecular ions in a string of ions. At every step, we will develop theoretical models and conduct numerical simulations to guide the experiments. These experiments and findings will pave the way toward high-resolution vibrational spectroscopy of SrH+ for applications in quantum technologies and in fundamental physics, in particular to search for new physics beyond the standard model.

Skills gained: Typically, PhD students working on an experimental setup dedicated to the trapping and cooling of ions, atoms or molecules acquire multiple technical skills not only in quantum sciences and technologies but also in laser physics, optics, rf-electronics, low-noise electronics, programming, ultra-high vacuum design, and for this topic precision measurements and metrology. These diverse skills are all assets that will contribute to open up very good career prospects both in and outside academia.

Bibliography:

[1] K. Mølhave and M. Drewsen, “Formation of translationally cold MgH+ and MgD+ molecules in an ion trap,” Phys. Rev. A, vol. 62, p. 011401, Jun 2000.

[2] K. Højbjerre et al., “Rotational state resolved photodissociation spectroscopy of translationally and vibrationally cold MgH+ ions,” New Journal of Physics, vol. 11, p. 055026, may 2009.

[3] R. Rugango et al., “Vibronic spectroscopy of sympathetically cooled CaH+,” ChemPhysChem, vol. 17, pp. 3764–3768, aug 2016.

[4] A. T. Calvin et al., “Rovibronic spectroscopy of sympathetically cooled 40CaH+,” The Journal of Physical Chemistry A, vol. 122, pp. 3177–3181, mar 2018.