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arXiv:2001.11616 · Physical Review A

Realization of a cold mixture of fermionic chromium and lithium atoms

E. Neri, A. Ciamei, Cristiano Simonelli, Irene Goti, M. Inguscio, A. Trenkwalder, Matteo Zaccanti

Published Jun 1, 2020• 22 citations
arXivHTMLPDF

Abstract

We report on the production of a cold mixture of fermionic $^{53}\mathrm{Cr}$ and $^{6}\mathrm{Li}$ atoms delivered by two Zeeman-slowed atomic beams and collected within a magneto-optical trap (MOT). For lithium, we obtain clouds of up to $4\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms at temperatures of about $500\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{K}$. A gray optical molasses stage allows us to decrease the gas temperature down to $45(5)\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{K}$. For chromium, we obtain MOTs of more than $1.1\ifmmode\times\else\texttimes\fi{}{10}^{6}$ atoms. The availability of magnetically trappable metastable $D$ states, from which $P$-state atoms can radiatively decay onto, enables to accumulate into the MOT quadrupole samples of almost ${10}^{7}$ $^{53}\mathrm{Cr}$ atoms. After repumping $D$-state atoms back into the cooling cycle, a final cooling stage decreases the chromium temperature down to $145(5)\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{K}$. While the presence of a lithium MOT decreases the lifetime of magnetically trapped $^{53}\mathrm{Cr}$ atoms, we obtain, within a 5-s duty cycle, samples of about $4\ifmmode\times\else\texttimes\fi{}{10}^{6}$ chromium and $3\ifmmode\times\else\texttimes\fi{}{10}^{8}$ lithium atoms. Our work provides a crucial step toward the production of degenerate Cr-Li Fermi mixtures.

DOI
10.1103/physreva.101.063602

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We report on magneto-optical trapping of fermionic 53Cr^{53}\mathrm{Cr}53Cr atoms. A Zeeman-slowed atomic beam provides loading rates up to $3\ifmmode\times\else\texttimes\fi{}{10}^{6}\phantom{\rule{0.3em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. We present systematic characterization of the magneto-optical trap (MOT). We obtain up to $5\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms in the steady-state MOT. The atoms radiatively decay from the excited PPP state into metastable DDD states, and, due to the large dipolar magnetic moment of chromium atoms in these states, they can remain magnetically trapped in the quadrupole field gradient of the MOT. We study the accumulation of metastable 53Cr^{53}\mathrm{Cr}53Cr atoms in this magnetic trap. We also report on the simultaneous magneto-optical trapping of bosonic 52Cr^{52}\mathrm{Cr}52Cr and fermionic 53Cr^{53}\mathrm{Cr}53Cr atoms. Finally, we characterize the light-assisted collision losses in this Bose-Fermi cold mixture.
We report on the realization of a degenerate mixture of ultracold fermionic lithium and chromium atoms. Based on an all-optical approach, with an overall duty cycle of about 13 s, we produce large and degenerate samples of more than $2\ifmmode\times\else\texttimes\fi{}{10}^{5}{\phantom{\rule{4pt}{0ex}}}^{6}\mathrm{Li}$ atoms and ${10}^{5}^{53}\mathrm{Cr}$ atoms, with both species exhibiting normalized temperatures of about T/TF=0.25T/{T}_{F}=0.25T/TF​=0.25. Additionally, through the exploitation of a crossed bichromatic optical dipole trap, we can controllably vary the density and degree of degeneracy of the two components almost independently and widely tune the lithium-to-chromium density ratio. Our $^{6}\mathrm{Li}\text{\ensuremath{-}}^{53}\mathrm{Cr}$ Fermi mixture opens the way to the investigation of a variety of exotic few- and many-body regimes of quantum matter and it appears as an optimally suited system to realize ultracold paramagnetic polar molecules, characterized by both electric and magnetic dipole moments. Ultimately, our strategy also provides an efficient pathway to produce dipolar Fermi gases, or spin mixtures, of ultracold 53Cr^{53}\mathrm{Cr}53Cr atoms.
In the perspective of studying dipole-dipole interactions in quantum degenerate Bose and Fermi gases, we have built an experimental setup for cooling and trapping Chromium (Cr) atoms. In this respect, one needs to use appropriate technological solution, such as a high-temperature oven (∼ 1500◦C) and a laser system providing high laser power at 425nm. Our experiments allow us to obtain magneto-optical traps for the two main isotopes of Cr (i.e. the bosonic 52Cr and the fermionic 53Cr). These traps are characterized by large light-assisted collisional loss rates, which have been studied both experimentally and theoretically. The existence of radiative decay channels towards two long-lived metastable states allows the magnetic trapping and accumulation of fairly large atom numbers of cold Cr atoms. We have studied the possibility of modifying the shape of these traps with the use of RF magnetic fields, which allowed the study of collisional properties of Cr atoms in the metastable states. Finally, we have demonstrated a new continuous loading technique of an optical dipole trap with more than one million metastable 52Cr atoms, at 100μK. The transfer into the ground state and the polarization in the lowest-energy Zeeman sublevel opens the perspective for reaching the Bose-Einstein condensation of Cr through evaporative cooling.
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We demonstrate a dual magneto-optical trap (MOT) of 109Ag^{109}\mathrm{Ag}109Ag and 39K^{39}\mathrm{K}39K. For silver, a decreasing-field Zeeman slower loads a MOT of $1.5\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms at a temperature of 0.74(5) mK, with laser cooling occurring primarily on the D2{D}_{2}D2​ line of $4{d}^{10}5s\phantom{\rule{0.28em}{0ex}}^{2}S_{1/2}\ensuremath{\rightarrow}5p\phantom{\rule{0.28em}{0ex}}^{2}P_{3/2}$ at 328 nm. We create a Ag ``dark spot MOT,'' where shelving the atoms in a dark state enhances the captured atom number by a factor of 2 and the lifetime by a factor of 4. For potassium, we obtain $2\ifmmode\times\else\texttimes\fi{}{10}^{8}$ trapped atoms, and further cooling on the D1{D}_{1}D1​ transition via gray molasses results in a cloud of $1.2\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms at $7(1)\phantom{\rule{0.28em}{0ex}}\textmu{}\mathrm{K}$. We observe evidence of photoionization loss of the K MOT in the presence of Ag laser-cooling light, necessitating sequential rather than simultaneous loading for the two species. Our results on Ag point to simple and general laser cooling strategies for other coinage metals (Au, Cu). Furthermore, this work lays the foundation for the production of alkali-metal--coinage-metal degenerate quantum mixtures and highly polar molecules.
Integrating two chemically distinct atomic species into a miniaturized, high-flux cold-atom source is a key challenge for modern experiments with ultracold atomic mixtures and polar molecules.Here, we report a compact setup with in-series two-dimensional magneto-optical traps (2D MOTs) that provides high-flux cold lithium and rubidium atoms.Thanks to the efficient short-distance Zeeman slowing, the maximum 3D MOT loading rate of lithium atoms reaches a record value of 6.6 × 10 9 atoms/s at a moderate lithium-oven temperature of 372 degrees Celsius, which is 44 times higher than that without the Zeeman slowing light.The flux of rubidium is also as high as 2.3 × 10 9 atoms/s with the rubidium oven held at room temperature.Meanwhile, the entire vacuum-chamber system, including an ultra-high-vacuum science cell, is within a small volume of 65 × 55 × 70 cm 3 .Our work represents a substantial improvement over traditional bulky and complex dual-species cold-atom setups.It provides a good starting point for the fast production of a double-degenerate lithium-rubidium atomic mixture and large samples of ultracold lithium-rubidium ground-state molecules.