Quantum gases of paramagnetic polar molecules, namely compounds that combine a large electric dipole moment with a magnetic one, associated with a nonzero electronic spin, are regarded as pristine platforms for a wealth of quantum-technological applications and fundamental studies ranging from quantum simulation and computation to controlled quantum chemistry and precision measurements. Yet realization of quantum gases of doubly polar molecules, based on biatomic systems considered so far, remains an unsurpassed task. In our joint experimental and theoretical work, we solve this two-decade-old challenge by exploring a new class of paramagnetic polar molecules, obtained by binding lithium alkali and transition-metal chromium elements. Starting from an ultracold mixture of 6⁢Li and 53⁢Cr fermionic atoms, we efficiently produce a high phase-space-density, long-lived gas of bosonic 6⁢Li53⁢Cr dimers, prepared within a single, weakly bound vibrational level. Through state-of-the-art techniques and novel probing methods, we reveal the paramagnetic nature of this diatomic species, gain experimental control over its internal quantum state, and identify the main inelastic mechanisms that may limit the system stability. In parallel, we develop quantum-chemical calculations to build a complete model for the LiCr molecule. We predict a large electric dipole moment together with high electronic spin in the absolute ground state, and we identify suitable transitions both for the coherent transfer of our weakly bound LiCr dimers to their lowest rovibrational level and for their subsequent optical manipulation. Our studies establish an unparalleled new pathway to realize quantum gases of doubly polar molecules, with countless future applications in quantum science and technology.

S. Finelli et al.
Ultracold Li⁢Cr: A New Pathway to Quantum Gases of Paramagnetic Polar Molecules
PRX Quantum (2024)

Beatrice successfully defends her Master's thesis titled ["Realization and characterization of LiCr ultracold bosonic dimers"], and starts her PhD on few-body physics and impurity problems in resonantly interacting Fermi mixtures.

Congrats and good luck Bea!

Max Schemmer has joined the LiCr team as Senior researcher.
Max has previously worked on 1-D quantum gases during his PhD under supervision of Isabelle Bouchoule (Laboratoire Charles Fabry, Palaiseau, France), and has has later worked as Marie-Curie fellow on quantum optics with cold atom-optical nanofiber hybrid platforms in the group of Arno Rauschenbeutel (Humboldt Universität zu Berlin).

Viel Glück Max!

Alessio Ciamei and Max Schemmer have both won the "Young Researcher" grant funded by the Italian Ministry of University and Research (MUR) with 300k€, each for the next 3 years.
A. C. will realize an ultracold gas of Polar Paramagnetic Molecules (PoPaMol) of LiCr and exploit this new class of molecules to perform ultracold chemistry studies and high precision spectroscopy.
M. S. plans to reveal Majorana states in Li-Cr p-wave superfluids, paving the way for topological quantum computing (MajorSuperQ).

Buona fortuna a entrambi!

We have reached simultaneous quantum degeneracy for fermionic Li and Cr atoms for the first time. In this work, we explain our all-optical strategy to realize large samples of more than 2x10^{5 6}Li and 10^{5 53}Cr atoms with T/T_F as low as 0.25 in less than 13 s. Moreover, by use of a crossed bichromatic optical dipole trap, we are able to control the relative density and degree of degeneracy of the mixture components. This novel mass-imbalanced Fermi mixture, which we already proved to possess suitable Feshbach resonances in a previous work [Phys. Rev. Lett. 129, 093402 (2022)], opens the way to the observation of novel exotic few- and many-body phenomena, as well as the creation of ultracold polar paramagnetic LiCr molecules. Finally, our experimental methods can be exploited to realize large Fermi gases or homonuclear spin-mixtures of ⁵³Cr, which will enable us to investigate the effects of weak dipolar interactions on BEC-BCS crossover physics.

Our results have been recently published in Physical Review A:

A. Ciamei et al.
Double-degenerate Fermi mixtures of ⁶Li and ⁵³Cr atoms
Phys. Rev. A 106, 053318 (2022)

Our preprint on ultracold collisions in 6Li-53Cr mixtures is now on the arXiv! We have performed extensive Feshbach spectroscopy of various spin combinations revealing more than 50 resonances between 0 and 1500 G. By means of a full coupled-channel model, we have unambiguously assigned a complete set of quantum numbers to each resonance and derived a thorough characterization of the scattering properties of our system. This has enabled us to identify several resonances suitable for future few-body and many-body studies of mass-imbalanced Fermi mixtures. What is more, our work paves the way to the production of a new class of ultracold molecules possessing both electric and magnetic dipole moments.

Stay tuned!

A. Ciamei et al.
Exploring ultracold collisions in ⁶Li-⁵³Cr Fermi mixtures: Feshbach resonances and scattering properties of a novel alkali-transition metal system
arXiv:2203.12965 (2022)

Within the CriLiN project, EU-funded through a Marie Skłodowska-Curie action, Alessio will develop a novel type of atomic quantum simulator with long-range, multi-body interactions.

In the middle of the hot Tuscan summer, we could bring to quantum degeneracy large samples of ⁶Li atoms in our setup. With the same all-optical strategies already developed in the LiLab, we can achieve crossover superfluids, as well as highly degenerate Fermi gases, of up to 1 million atoms. (In the image, the hydrodynamic expansion of a crossover superfluid of about 700000 pairs).

We brought into the cold regime the first chromium-lithium fermionic mixture worldwide. within a 5 sec. duty cycle, we produce samples of about 4 million chromium and 300 million lithium atoms at a few hundreds of microKelvin. Our work just got published in Phys. Rev. A.

E. Neri, et al.,
Realization of a cold mixture of fermionic chromium and lithium atoms
Phys. Rev. A 101, 063602 (2020)

Together with Wilhelm Zwerger, we developed a simple analytic model to quantitatively describe the Josephson tunneling between two Fermi superfluids along the entire BCS-BEC crossover. Our work just got published in Phys. Rev. A.

M. Zaccanti, W. Zwerger,
Critical Josephson current in BCS-BEC–crossover superfluids
Phys. Rev. A 100, 063601 (2019)

We devised a simple, totally passive scheme that enables to realize an inexpensive optical trapping apparatus free from thermal lensing effects. Our work just got published in Optics Express.

C. Simonelli et al.,
Realization of a high power optical trapping setup free from thermal lensing effects
Opt. Express 27, 27215 (2019)

We have finalized the construction of the experimental setup, and we're now able to produce the first Lithium-Chromium MOT worldwide! Fun has just begun!

We have completed the design of the dual-species vacuum setup of the experiment and its construction will begin very soon. Stay tuned for updates!

We have recently developed a home-made and unexpensive high power laser source @425nm: up to 800mW of blue light for laser cooling of Chromium!

Matteo Zaccanti has been awarded with an ERC Starting Grant! The title of the project is "PoLiChroM: Superfluidity and ferromagnetism of unequal mass fermions with 2- and 3-body resonant interactions” (proposal #637738). Congratulations!