Periodic Reporting for period 4 - CoMoQuant (Correlated Molecular Quantum Gases in Optical Lattices)
Période du rapport: 2023-07-01 au 2023-12-31
The project has a diverse list of goals. The primary goal is to generate quantum-degenerate dipolar gases of bosonic and fermionic K-Cs molecules and to carry out diverse experiments with such a novel type of quantum matter in the context of superfluidity, supersolidity, and lattice spin physics. Many of these experiments shall be carried out in a regime where access to the individual molecules for control and imaging is given, similar to present approaches with ultracold atomic gases in a quantum-gas microscope setting. In order to get to this point, the generation of ultracold samples of K-Cs molecules has to be mastered. In view of the fact that molecules are not readily laser-coolable, an indirect approach, as previously demonstrated in other projects in our group and by various other groups worldwide, has been chosen: The ground-state molecules are to be generated out of quantum-degenerate atomic mixtures (here: Cs and K) by means of Feshbach association in combination with subsequent stimulated two-photon laser transfer known as STIRAP. In essence, as detailed below, all our efforts within this project over the past 3 years have been focused on achieving this intermediate goal.
We have implemented long-distance transport of ultracold atoms from the collection chamber to the all-quartz-glass science cell. A so-called Moire lens with a tunable focus allows us to transport atoms at a temperature of 11 microKelvin across a distance of 45 cm with negligible heating and a transport efficiency of 70%. Initial attempts to use a deformable lens (from the company Optotune) failed due to the strong astigmatism introduced by that lens and thermal instabilities, most likely due to the high laser power applied to the lens, leading to some absorption. We have been able to characterize the atom transport in detail and have written up and published a publication on its implementation. The transport characteristics look very promising and should allow transport also of quantum-degenerate atomic samples.
We have designed a new ultra-high vacuum chamber with a novel set of electrodes for molecule control and an in-vacuum objective for future single-molecule imaging. When transporting atoms into the existing science cell by the method mentioned above, we noticed that the lifetime of the atomic sample was only about 2 sec inside the science cell, in contrast to a lifetime of about 20 sec in the collection chamber (the vacuum conditions in the collection chamber are sufficiently good to allow us to produce quantum-degenerate samples of either Cs or K atoms). After extensive tests we were led to attribute this reduced lifetime to an outgassing problem, compromising greatly the vacuum conditions in that cell. In particular, we have not been able to find a real vacuum leak. We do not think that the outgassing problem is due to our electrode structure and the in-vacuum electrode holder. It is more likely that the quartz cell itself with its glued components is the culprit, with perhaps some virtual leaks on the glued connections. In view of this problem, we ordered a new quartz cell, this time from a different company with proven experience on UHV cells. A new electrode holder was designed. With the new cell, we will implement a series of improvements: For example, in contrast to the old cell, which contained only one in-vacuum lens, a high-resolution, vacuum compatible objective will be integrated. After extensive design studies, the company Special Optics was awarded the contract to manufacture this custom-made objective. After a long delay, the objective arrived and was tested by us. To the extent that we can test the objective (e.g. sufficient resolution) it has met the specifications.
We have now started to assemble the entire chamber with all the improvements that had been planned. In principle, all components, from the 2D-MOT loading cell and the atom source to the objective and electrode holders (inside the new quartz cell) are ready. First vacuum test have been performed. The chamber is awaiting its final assembly.
While setting up the new apparatus, we were working with the existing apparatus to find a quick route for simultaneous condensation of K and Cs atoms. In short, we have found a way of sympathetically cooling K and Cs atoms to near quantum degeneracy. We can create about 5000 KCs molecules by the Feshbach-association technique. We have identified a route for ground-state transfer and have implemented stimulated Raman adiabatic passage (STIRAP) with an efficiency of about 75% to the absolute rovibrational ground state of KCs. Presently, we are working on improving this transfer step. We are currently writing on two publications, one on the productions of the cold-atom mixture, and one on the STIRAP transfer.
Simultaneously, we have worked with quantum degenerate Cs samples alone. We have obtained a diverse set of results as summarized by the titles of the following publications: "Observation of the 2D-1D crossover in strongly interacting ultracold bosons", Yanliang Guo et al., Nature Physics 20, 934 (2024), "Anomalous cooling of bosons by dimensional reduction", Yanliang Guo et al., Science Advances 10, 6 (2024), "Bose-Einstein condensation of non-ground-state caesium atoms", Milena Horvath et al., Nature Communications 15, 3739 (2024), "Observation of many-body dynamical localization", Yanliang Guo et al., in review with a high-profile journal, preprint at: arxiv.org/abs/2312.13880 "Anyonization of bosons", Sudipta Dhar et al., in review with a high-profile journal, preprint at: arxiv.org/abs/2412.21131. Several further publications are nearing completion.
We have designed a new ultra-high vacuum chamber with a novel set of electrodes for molecule control and an in-vacuum objective for future single-molecule imaging. When transporting atoms into the existing science cell by the method mentioned above, we noticed that the lifetime of the atomic sample was only about 2 sec inside the science cell, in contrast to a lifetime of about 20 sec in the collection chamber (the vacuum conditions in the collection chamber are sufficiently good to allow us to produce quantum-degenerate samples of either Cs or K atoms). After extensive tests we were led to attribute this reduced lifetime to an outgassing problem, compromising greatly the vacuum conditions in that cell. In particular, we have not been able to find a real vacuum leak. We do not think that the outgassing problem is due to our electrode structure and the in-vacuum electrode holder. It is more likely that the quartz cell itself with its glued components is the culprit, with perhaps some virtual leaks on the glued connections. In view of this problem, we ordered a new quartz cell, this time from a different company with proven experience on UHV cells. A new electrode holder was designed. With the new cell, we will implement a series of improvements: For example, in contrast to the old cell, which contained only one in-vacuum lens, a high-resolution, vacuum compatible objective will be integrated. After extensive design studies, the company Special Optics was awarded the contract to manufacture this custom-made objective. After a long delay, the objective arrived and was tested by us. To the extent that we can test the objective (e.g. sufficient resolution) it has met the specifications.
We have now started to assemble the entire chamber with all the improvements that had been planned. In principle, all components, from the 2D-MOT loading cell and the atom source to the objective and electrode holders (inside the new quartz cell) are ready. First vacuum test have been performed. The chamber is awaiting its final assembly.
While setting up the new apparatus, we were working with the existing apparatus to find a quick route for simultaneous condensation of K and Cs atoms. In short, we have found a way of sympathetically cooling K and Cs atoms to near quantum degeneracy. We can create about 5000 KCs molecules by the Feshbach-association technique. We have identified a route for ground-state transfer and have implemented stimulated Raman adiabatic passage (STIRAP) with an efficiency of about 75% to the absolute rovibrational ground state of KCs. Presently, we are working on improving this transfer step. We are currently writing on two publications, one on the productions of the cold-atom mixture, and one on the STIRAP transfer.
Simultaneously, we have worked with quantum degenerate Cs samples alone. We have obtained a diverse set of results as summarized by the titles of the following publications: "Observation of the 2D-1D crossover in strongly interacting ultracold bosons", Yanliang Guo et al., Nature Physics 20, 934 (2024), "Anomalous cooling of bosons by dimensional reduction", Yanliang Guo et al., Science Advances 10, 6 (2024), "Bose-Einstein condensation of non-ground-state caesium atoms", Milena Horvath et al., Nature Communications 15, 3739 (2024), "Observation of many-body dynamical localization", Yanliang Guo et al., in review with a high-profile journal, preprint at: arxiv.org/abs/2312.13880 "Anyonization of bosons", Sudipta Dhar et al., in review with a high-profile journal, preprint at: arxiv.org/abs/2412.21131. Several further publications are nearing completion.
We expect that the new vacuum chamber will allow us to go significantly beyond the state-of-the-art in the field of ultracold quantum matter. It will allow us to image ultracold or even quantum-degenerate samples of molecules with single-site resolution in a quantum-gas microscope. Such microscopes are by now routine in many groups, but so far only for atomic samples. In our case, we need to integrate the high-resolution imaging capability with the (rather bulky) electrode structure, requiring a lens system that has a rather large working distance. Our primary goal is to demonstrate Bose-Einstein condensation of ground-state dipolar molecules. With this, we would have a new type of quantum matter in the laboratory for a multitude of quantum many-body applications.