Periodic Reporting for period 1 - TRITRAMO (Trimers,Tetramers and molecular BEC)
Reporting period: 2022-10-01 to 2025-03-31
This project aims to advance the field of ultracold quantum physics by exploring and controlling small polyatomic molecules in quantum gases. Building on expertise in controlling diatomic molecules, the research focuses on creating and studying weakly bound trimers (three-atom molecules) and tetramers (four-atom molecules) in ultracold environments. Using atom-molecule quantum gas mixtures of potassium (39K) and sodium-potassium (23Na39K), along with ion spectrometry for detection, the goal is to understand how molecular complexity affects quantum systems.
This work will deepen our understanding of how few-body quantum systems evolve as more atoms are added, provide tools for precise control of molecular collisions, and potentially lead to the first Bose-Einstein condensate (BEC) of polar molecules. These advancements would open new pathways for exploring dipolar quantum many-body physics and further the potential of ultracold molecular systems for quantum technologies.
This work will deepen our understanding of how few-body quantum systems evolve as more atoms are added, provide tools for precise control of molecular collisions, and potentially lead to the first Bose-Einstein condensate (BEC) of polar molecules. These advancements would open new pathways for exploring dipolar quantum many-body physics and further the potential of ultracold molecular systems for quantum technologies.
Over the past 30 months, significant advancements were made in exploring ultracold molecular systems, focusing on technical and scientific aspects.
Trimer Formation
Experimental Progress: Atom–molecule scattering in ultracold bosonic mixtures of ³⁹K and ²³Na³⁹K was studied. A rich spectrum of Feshbach resonances was identified, suggesting multiple candidate pathways for trimer formation. Notably, discrepancies between observed and predicted resonance positions revealed limitations in existing models, prompting the development of refined theoretical approaches.
Theoretical Progress: A dedicated photoassociation model was developed to describe long-range atom–molecule interactions. It enabled precise calculations of bound-state energies and photoassociation rates, offering insights into trimer dynamics and providing crucial support to experimental interpretation.
Microwave Photoassociation: A novel theoretical framework was established in which microwave electric fields drive dipole-allowed transitions between atom–molecule scattering states and weakly bound triatomic ground-state levels. This mechanism allows for the formation of ultracold triatomic molecules without the need for magnetic tuning, with predicted association rates well within reach of current experiments.
Tetramer Formation and Collisional Control
Experimental Challenge: Initial studies of collisions between ²³Na³⁹K molecules showed a high density of four-body states, rendering individual resonances unresolvable through standard magnetic tuning.
Theoretical Solution: In response, a two-photon optical shielding method was developed. This technique uses a pair of laser fields to couple ground-state molecules to electronically excited states in a coherent and species-independent manner. It induces long-range repulsive interactions that suppress short-range losses and enables optical control over collisional processes relevant to tetramer formation and stability.
Methodological Innovations
A high-flux, dual-species atom source for ³⁹K and ²³Na was implemented, significantly improving the efficiency and reproducibility of ultracold mixture preparation.
The development of both microwave- and laser-based interaction control schemes has significantly extended the toolbox available for engineering molecular interactions in the ultracold regime, laying the foundation for future studies of complex molecular assemblies and controlled quantum chemistry.
Trimer Formation
Experimental Progress: Atom–molecule scattering in ultracold bosonic mixtures of ³⁹K and ²³Na³⁹K was studied. A rich spectrum of Feshbach resonances was identified, suggesting multiple candidate pathways for trimer formation. Notably, discrepancies between observed and predicted resonance positions revealed limitations in existing models, prompting the development of refined theoretical approaches.
Theoretical Progress: A dedicated photoassociation model was developed to describe long-range atom–molecule interactions. It enabled precise calculations of bound-state energies and photoassociation rates, offering insights into trimer dynamics and providing crucial support to experimental interpretation.
Microwave Photoassociation: A novel theoretical framework was established in which microwave electric fields drive dipole-allowed transitions between atom–molecule scattering states and weakly bound triatomic ground-state levels. This mechanism allows for the formation of ultracold triatomic molecules without the need for magnetic tuning, with predicted association rates well within reach of current experiments.
Tetramer Formation and Collisional Control
Experimental Challenge: Initial studies of collisions between ²³Na³⁹K molecules showed a high density of four-body states, rendering individual resonances unresolvable through standard magnetic tuning.
Theoretical Solution: In response, a two-photon optical shielding method was developed. This technique uses a pair of laser fields to couple ground-state molecules to electronically excited states in a coherent and species-independent manner. It induces long-range repulsive interactions that suppress short-range losses and enables optical control over collisional processes relevant to tetramer formation and stability.
Methodological Innovations
A high-flux, dual-species atom source for ³⁹K and ²³Na was implemented, significantly improving the efficiency and reproducibility of ultracold mixture preparation.
The development of both microwave- and laser-based interaction control schemes has significantly extended the toolbox available for engineering molecular interactions in the ultracold regime, laying the foundation for future studies of complex molecular assemblies and controlled quantum chemistry.
The project has delivered several high-impact results that advance the frontiers of ultracold molecular physics and provide enabling tools for future developments in quantum science. These outcomes go significantly beyond the current state of the art in the control, formation, and understanding of complex ultracold molecular systems.
One major advance was the identification of a dense spectrum of Feshbach resonances in atom–molecule collisions between ³⁹K and ²³Na³⁹K. These findings offer critical insights into few-body quantum interactions and open a viable route toward sympathetic cooling of molecules—a key prerequisite for realizing molecular Bose-Einstein condensates (BECs) and chemically stable quantum matter.
The project also introduced a two-photon optical shielding method that enables species-independent suppression of collisional loss in ground-state polar molecules. This technique provides long-range repulsion using tailored optical fields and overcomes limitations of existing one-photon or microwave shielding schemes. It offers a highly versatile platform for engineering interaction potentials, with direct applications in quantum simulation, quantum-controlled chemistry, and precision measurements.
A further breakthrough was the theoretical development of microwave photoassociation, which enables the formation of weakly bound triatomic ground-state molecules by resonantly coupling atom–molecule scattering states using the electric-dipole interaction. This method provides an alternative to magnetic Feshbach resonances, is broadly applicable across species, and may play a central role in building larger molecular complexes in the ultracold regime.
To support these advances, the project also developed a long-range photoassociation model that predicts binding spectra and formation rates of atom–molecule complexes under laser coupling. This theoretical tool is essential for guiding future experiments and supports the efficient assembly of few-body molecular states under controlled conditions.
Potential Impacts and Future Needs
These results create new avenues for:
Realizing stable ultracold molecular ensembles for quantum technology platforms
Advancing the formation of larger molecules (e.g. tetramers) with tunable interactions
Enabling precision control over quantum-state-resolved collisions and reactions
Key needs for further uptake and success include:
Continued experimental validation of the proposed optical and microwave association schemes
Development of laser and microwave sources with sufficient stability and control for coherent association processes
Interdisciplinary collaborations to integrate these techniques into quantum simulation architectures
One major advance was the identification of a dense spectrum of Feshbach resonances in atom–molecule collisions between ³⁹K and ²³Na³⁹K. These findings offer critical insights into few-body quantum interactions and open a viable route toward sympathetic cooling of molecules—a key prerequisite for realizing molecular Bose-Einstein condensates (BECs) and chemically stable quantum matter.
The project also introduced a two-photon optical shielding method that enables species-independent suppression of collisional loss in ground-state polar molecules. This technique provides long-range repulsion using tailored optical fields and overcomes limitations of existing one-photon or microwave shielding schemes. It offers a highly versatile platform for engineering interaction potentials, with direct applications in quantum simulation, quantum-controlled chemistry, and precision measurements.
A further breakthrough was the theoretical development of microwave photoassociation, which enables the formation of weakly bound triatomic ground-state molecules by resonantly coupling atom–molecule scattering states using the electric-dipole interaction. This method provides an alternative to magnetic Feshbach resonances, is broadly applicable across species, and may play a central role in building larger molecular complexes in the ultracold regime.
To support these advances, the project also developed a long-range photoassociation model that predicts binding spectra and formation rates of atom–molecule complexes under laser coupling. This theoretical tool is essential for guiding future experiments and supports the efficient assembly of few-body molecular states under controlled conditions.
Potential Impacts and Future Needs
These results create new avenues for:
Realizing stable ultracold molecular ensembles for quantum technology platforms
Advancing the formation of larger molecules (e.g. tetramers) with tunable interactions
Enabling precision control over quantum-state-resolved collisions and reactions
Key needs for further uptake and success include:
Continued experimental validation of the proposed optical and microwave association schemes
Development of laser and microwave sources with sufficient stability and control for coherent association processes
Interdisciplinary collaborations to integrate these techniques into quantum simulation architectures