By adjusting the parameters of the two beams, in the figures assumed to feature equal waists and an IR-to-green power ratio of 2, one can obtain an overall BODT potential (black curves) deeper for the Cr than for the Li component. The IR light (red curves) yields a trapping potential about 3.3 times deeper for Li than for Cr atoms, whereas the green beam (green curves) anticonfines lithium and tightly confines chromium (see the text for details). (a) Sketch of the optical potentials experienced by Li (left) and Cr (right) atoms confined in the BODT. The three green transitions around 533 nm, coupling the 7 P 4 to the 7 D 3, 4, 5 states, are relevant for the operation of the dark spot discussed in Sec. Here R R 1 and R R 3, detuned from each other by only 225 MHz, are obtained by two separate sets of acousto-optic modulators. These lights are delivered by two independent master oscillators at 663 and 654 nm (see Ref. for more details). Metastable D 5 states onto which 7 P 4 atoms decay by spontaneous emission are repumped back into the cooling cycle by three additional red repumper beams labeled as R R 1, R R 2, and R R 3, with the same indexing used for B R. A single frequency-doubled laser at 425.5 nm delivers the light exciting atoms from 7 S 3 to 7 P 4, addressing the main cooling transition labeled “Cooler” (solid blue), and the repumping transitions denoted by B R 1, B R 2, and B R 3 (dashed blue) in order of decreasing gain on the steady-state MOT number. For each relevant hyperfine level originating from the nonzero nuclear spin I = 3 / 2, the F quantum number and the detuning Δ in MHz, referenced to an assumed I = 0 state, are shown. Sketch of energy levels and optical transitions addressed for the laser cooling of Cr 53 atoms (not to scale). Ultimately, our strategy also provides an efficient pathway to produce dipolar Fermi gases, or spin mixtures, of ultracold Cr 53 atoms. Our Li 6 − Cr 53 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. 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. 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 × 10 5 6 Li atoms and 10 5 Cr 53 atoms, with both species exhibiting normalized temperatures of about T / T F = 0.25. We report on the realization of a degenerate mixture of ultracold fermionic lithium and chromium atoms.
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