CE30 - Physique de la matière condensée et de la matière diluée

COllisions in a COld TRApped MOlecular Sample in a well-defined quantum state – COCOTRAMOS

Submission summary

The research field of ultracold (T<<1mK) molecules involves an increasing number of groups throughout the world, due to their foreseen applications in quantum technologies and cold chemistry. Molecules at ultracold temperatures can be precisely controlled in both their translational motion and their internal quantum states. Unfortunately, until recently, laser cooling could not be applied easily to molecules because they generally do not possess suitable closed optical transitions, like in atomic systems: their complex internal structure, prevents them from transferring cooling and slowing methods known from atomic physics, except for a very restricted class of molecular species .

The main goal of the current proposal is to refine laser cooling further, to invent new cooling schemes which take into account the unique features of molecular structure, and produce a dense sample of absolute ground state of cold trapped Rb2 molecules. We intend to study bi-molecular collisions in two directions: first by finding optimal conditions to suppress them by optical shielding, and second to observe molecule-molecule collisions, possibly assisted by light, eventually forming Rb4 polyatomic molecules.

The proposal is built upon three main objectives mixing experimental and theoretical aspects:

(i) The experimental achievement of laser-cooling and trapping of Rb2 molecules from a supersonic molecular beam, guided by simulations elaborated using molecular structure calculations. For this aim, we will implement a rovibrational optical pumping technique, which will act like a broad-band repumping light source, thus imposing a “closed optical transition” to the molecules.

(ii) The investigation of suppression of bi-molecular collisions using optical laser light which is blue-detuned from a suitable electronic molecular transition. Increasing the shielding efficiency will be of great interest for experimentalists whose aim is to obtain high density long-lived samples of ultracold molecules, paving the way to quantum degeneracy.

(iii) The search for ultracold inelastic and reactive collisions between Rb2 molecules, possibly assisted by light, including photoassociation and formation of stable Rb4 molecules. Photoionization mass spectroscopy will allow us to identify the species present in the sample (Rb, Rb2, Rb3 , Rb4). Such processes exemplify a novel ultracold chemistry, intuitively assumed to be dominated by the long-range interactions between the reacting particles, but possibly with a complex interplay with short-range dynamics. This is still an open question, since the large amount of resonances of the collisional complex may give rise to a long-lived complex at short distances. The detection of photoassociation lines may provide an experimental insight into the role of these resonances in the dynamics.

This work is a continuation of a successful long collaboration between the Brazilian USP-SC experimental group and the French LAC theoretical team. Together they have made a series of achievements including the successful creation of ultracold ground state rubidium diatomic molecules by short range photoassociation. Four joint scientific papers have been published within this collaboration since 2013.

Project coordination

NADIA BOULOUFA (Laboratoire Aimé Cotton)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.


LAC Laboratoire Aimé Cotton
USP-SC Instituto de Física de São Carlos, Universidade de São Paulo, Brasil / Instituto de Física de São Carlos

Help of the ANR 189,761 euros
Beginning and duration of the scientific project: January 2022 - 48 Months

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