CriLiN was articulated in three main concurrent objectives:
1) Investigation of inter-species Feshbach resonances.
As soon as Li and Cr were brought to the ultracold regime, we focused onto Feshbach spectroscopy [1]. We investigated several spin combinations and performed extensive magnetic field scans unveiling more than 50 inter-species resonances. Thanks to our collaboration with theorist Prof. Andrea Simoni, we assigned a complete set of quantum numbers to each observed resonance and developed an accurate quantum collisional model. The Li-Cr system features a rich but non-chaotic Feshbach spectrum with both s-wave and p-wave well-resolved resonances with negligible two-body losses in several spin states and magnetic fields between 0G and 1500G. We concentrated our attention to s-wave resonances with largest magnetic field width (0.5 G) above 1.4 kG in lowest lying Zeeman levels, which we thoroughly characterized and used to demonstrate resonant tuning of the elastic interactions. We showed that the Feshbach spectrum is suitable for many-body physics studies. On top of that also a few intra-species Cr resonances were observed, setting the basis for future investigation of resonantly interacting homonuclear mixtures of Cr53.
2) Realization of a degenerate 6Li-53Cr Fermi mixture.
Before CriLiN, we had already shown double magneto-optical-trap (MOT) of Li and Cr atoms. In order to reach double degeneracy, we improved the Cr MOT number by two orders of magnitude, and devised an efficient way to transfer Cr atoms directly from the MOT to a bichromatic optical dipole trap, together with Li. Forced evaporation of Li and simultaneous sympathetic cooling of Cr was sufficient to reach the ultracold uK regime, and allowed us to work in parallel on objective 1). This proved crucial, since the understanding of collisional properties informed us on the best strategy to reach quantum degeneracy. In fact, we exploited sympathetic cooling enhanced by a narrow Feshbach resonance to achieve our goal (paper in preparation). Deeper degeneracy was obtained by changing trap geometry from single to cross-beam trap. We simultaneously realize large, degenerate and spin-polarixed samples of 200k Li and 100k Cr with normalized temperature of 0.25 with a 13s overall duty cycle [2]. This performance shows that this mixture is suitable for the practical realization of a quantum simulator. Details on the experimental apparatus and the experimental sequence can be found in [3].
3) Few-body interactions and mixture stability.
Still focusing on high-field s-wave resonances, we measured the lifetime of our mixture as function of the detuning from the resonance pole for several spin-state combinations. Experimental data showed evidence for Feshbach LiCr molecule creation and loss. Thus, we exploited the very same resonances for demonstrating production of large samples of up to 60k bosonic LiCr dimers at 200nK via magneto-association (paper in preparation). We measured the magnetic moment of such a molecule, confirming the assignment of our theory collaborator.
[1] A. Ciamei et al., Phys. Rev. Lett. 129, 093402 (2022)
[2] A. Ciamei et al., preprint arXiv:2207.07579 (2022)
[3] S. Finelli, Master Thesis (University of Florence, 2022)
