Description du sujet de thèse

The violation of the fundamental parity and time-reversal symmetries is manifested in the atom through the appearance of an electric dipole, magnetic quadrupole or Schiff moment. In molecules these effects can be enlarged by more than five orders of magnitude because of the occurrence of doublets of opposite parity with extremely small energy splittings. Heavy nuclei with octupolar deformation may enhance the symmetry breaking even further, ultimately making it possible to probe the violation by dedicated high-precision experiments, particularly in systems that contain francium atoms, radium or any of the actinide elements beyond.
However, to experimentally constrain a broken fundamental symmetry in a molecule still appears beyond our present-day reach. Great technical progress has been achieved over the last 20 years and has been applied to atomic systems, but the molecular realm stands unexplored. While some of the compound species that are promising for these measurements have been identified from theoretical considerations and corresponding opportunies at accelerator laboratories have been put forward, the spectroscopic properties of many of them remain entirely unknown. The energies and configurations of excited states, the ionisation potential, and in particular, the practical conditions that must allow for the necessary laser cooling have not been established. Only for radium and actinium monofluoride molecular laser spectroscopy was achieved in collinear resonance ionisation spectroscopy some years ago. These experiments were remarkably successful, as it was possible through accurate theoretical predictions to narrow down the search range for the parameters of interest, much shortening the time that was needed to obtain significant results.
Within our collaboration with the Ganil laboratory in Caen (France) and the Triumf accelerator facility in Vancouver (Canada) we have decided to seize the momentum and take advantage of our existing experimental installations both in France and Canada to contribute to this interface of nuclear and molecular physics that is with direct relevance for our understanding of nature's fundamental interactions. Our primary focus lies on producing the cold molecules in the appropriate quantum state in a gas jet at Ganil and participate in ongoing photo-association experiments of francium molecules at Triumf.
At this time, the ambient temperature of the molecules when they interact with the laser light obscures any sensitivity to fundamental symmetries. Laser cooling is regarded as one of the most efficient ways forward to reach the required temperatures of the order of some millikelvin, but the gap when starting from a sample at room temperature is large to bridge. Our experiments at Ganil, however, present us with an favourable alternative. Isotopes of heavy elements such as actinides can be produced and injected in a jet of argon gas. The supersonic expansion of the gas provides temperatures of 20 mK, well suited for subsequent laser cooling and preparing the molecular cloud for tests of fundamental symmetries.
In a first course of action, stable lanthanum ions will be produced from a filament and neutralised by collisions in the gas flow. Because of the presence of residual water in the experimental set-up, there is a high likelihood for the formation of molecules such as LaO and LaOH in this process. We shall ionise these by means of resonant laser irradiation in the gas jet, meanwhile scanning the wavelengths of so-far unknown excited states and determining the ionisation potential. The molecular ion is then extracted and transported to a multireflection time-of-flight mass spectrometer for identification.
In a second stage of the thesis we shall introduce radioactive actinides from a long-lived source in the experiment and repeat our systematic studies of molecular formation, excitation and ionisation with it. Notably the AcO and AcOH molecules would be major targets for the measurement of the parity and time-reversal violating Schiff moment.

The candidate recruited will have to prepare and participate in experiments at Ganil and Triumf. Analyse the data that are obtained by means of available or newly developed computer codes. Collaborate with theoreticians to interpret the results. Write reports and present these at workshops and conferences.

Contexte de travail

Radioactive molecules have recently emerged as precision probes for anomalous electromagnetic moments, offering unprecedented sensitivity to parity and time-reversal violation. Despite their immense physics potential, the necessary experimental techniques are still in their early stages. They often rely on the translation of cutting-edge technology in atomic, molecular, and optical physics into accelerator laboratories, such as Ganil in Caen (France) and Triumf in Vancouver (Canada), where these radionuclides are uniquely produced.
To advance the novel field of radioactive molecules both at Ganil and Triumf, a collaboration has been established between CNRS and the university of British Columbia (UBC). The supersonic gas jet at Ganil is an innovative and exceptional instrument for the investigation of nuclear moments by means of laser spectroscopy. It has recently been commissioned with lanthanide atoms and is available for studies with stable or long-lived species, to which our present proposal for laser spectroscopy of molecules bears witness. Likewise, the initiative will enable researchers to conduct precision studies and new-physics searches by exploring radioactive molecules that incorporate the heavy francium atom at Triumf.
The CNRS-UBC joint PhD fellowship program thus represents an opportunity to connect researchers from CNRS and UBC, facilitating knowledge exchange across different research programs to identify the most effective experimental techniques for forming cold radioactive molecules. The two accelerator laboratories complement one another in several aspects, including radionuclide production as well as atom and molecule formation and cooling (such as supersonic expansion at Ganil and assembly from laser-cooled atoms at Triumf). The fellowship program is a key element in strengthening the recently established CNRS international research laboratory at Triumf.
The Irène Joliot-Curie laboratory (IJCLab) managed by the CNRS, the university of Paris-Saclay and the university of Paris is located on the Orsay campus of the university of Paris-Saclay, 30 km south of Paris and accessible by public transport. Its staff is constituted of more than 500 permanent members (researchers, teachers, engineers, technicians and administrators) and 200 non-permanent members (including 100 doctoral students). The research themes of the laboratory comprise nuclear physics, high-energy physics, theoretical physics, astroparticles, cosmology, particle accelerators, energy and health. IJCLab covers all technical capabilities to design, develop and implement the experimental devices necessary for its scientific activity.
The successful PhD candidate will work in the Spectroscopy-Decay-Fission group of the nuclear division of the laboratory, which includes about ten physicists (researchers, post-docs and doctoral students), who carry out their experiments on the structure of the atomic nucleus in various laboratories around the world.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.

Contraintes et risques

Travel to Caen (France, once or twice per month) and Vancouver (Canada, once or twice per year) are essential parts of the thesis.

Informations complémentaires

The candidate must have a degree in physics or engineering, preferentially with a basic knowledge of nuclear physics. The application shall include a letter of motivation and curriculum vitae with relevant grades, diplomas, titles and professional experience. One or two letters of recommendation with names and contact details of former supervisors or teachers are advisable. Proficiency in English is necessary. Critical thought, analytical evaluation, organisational skills, the ability to work independently and responsably, creativity, initiative, adaptability, resilience are highly appreciated.

The successful candidate will be enrolled in the doctoral school of the university of Paris-Saclay. Hiring at IJClab is subject to approval by the Haut Fonctionnaire Securité & Défense, which may induce delay in the date of employment stated above.

IJClab bases its recruitment policy on the promotion of equality and inclusion.