Simultaneous magneto-optical trapping of bosonic and fermionic chromium atoms

We report on magneto-optical trapping of fermionic ${}^{53}\mathrm{Cr}$ atoms. A Zeeman-slowed atomic beam provides loading rates up to $3\times {10}^6{\mathrm{s}}^{-1}$. We present systematic characterization of the magneto-optical trap (MOT). We obtain up to $5\times {10}^5$ atoms in the steady-state MOT. The atoms radiatively decay from the excited $P$ state into metastable $D$ 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 ${}^{53}\mathrm{Cr}$ atoms in this magnetic trap. We also report on the simultaneous magneto-optical trapping of bosonic ${}^{52}\mathrm{Cr}$ and fermionic ${}^{53}\mathrm{Cr}$ atoms. Finally, we characterize the light-assisted collision losses in this Bose-Fermi cold mixture.

Figure 1

Relevant energy levels for cooling and trapping ${}^{52}\mathrm{Cr}$ and ${}^{53}\mathrm{Cr}$ including the leaks to metastable states and (bottom) sketch of the laser frequencies used in our experiment ($\delta$ and ${\delta }^{\prime }$ stand for the MOT detunings). Transition probabilities to the bosonic metastable states are from [9]; hyperfine structure splitting of the fermionic isotope is from [10]. We deduced from our experiment the isotopic shift between the ${}^{52}\mathrm{Cr}$ ${}^{7}S_3\to {}^{7}P_4$ transition and the ${}^{53}\mathrm{Cr}F=7∕2\to F^{\prime }=9∕2$ transition to be $6\pm 1\mathrm{MHz}$.

Figure 2

(Color online) Schematic of the experimental chamber showing the MOT beams, the coupling of the ZS beam, and the MOT fluorescence detection. $L$, lens; $\lambda ∕4$, quarter wave plate; BS, beam splitter; V, vertical; H, horizontal. The inset shows a plot of the experimental ZS magnetic field in gauss as a function of the $z$ position along its axis in meters. See text for a discussion of the three zones.

Figure 3

(Color online) Atom number (dots) and peak atom density (triangles) in the ${}^{53}\mathrm{Cr}$ MOT as a function of the normalized detuning of the MOT cooling beam compared to the $\mid {}^{7}S_3,F=9∕2⟩$ to $\mid {}^{7}P_4,F=11∕2⟩$ transition, with a total laser intensity of the MOT beams equal to $200\mathrm{mW}{\mathrm{cm}}^{-2}$. Error bars show the dispersion over four data points, and the solid line is a guide for the eye.

Figure 4

(Color online) Atom number (dots) and peak atom density (triangles) in the ${}^{53}\mathrm{Cr}$ MOT as a function of the total power in the MOT cooling beams, for a detuning of the MOT beams equal to $-21.5\mathrm{MHz}$. Error bars show the dispersion over four data points, and the solid line is a guide for the eye.

Figure 5

(Color online) Loading sequences for simultaneous magneto-optical trapping of ${}^{52}\mathrm{Cr}$ and ${}^{53}\mathrm{Cr}$ atoms. The MOT for ${}^{52}\mathrm{Cr}$ atoms is turned on at $t=0$, whereas the AOMs for the ${}^{53}\mathrm{Cr}$ MOT are only turned on during the time period indicated by the two vertical dashed lines. (a) Small number of atoms: when the ${}^{53}\mathrm{Cr}$ MOT is turned off, the remaining fluorescence signal of ${}^{52}\mathrm{Cr}$ atoms is identical to the one before the ${}^{53}\mathrm{Cr}$ MOT was turned on, which means that no mutual effects took place. The solid line is the result of a fit only taking into account fluorescence of bosons. (b) Large number of atoms: after ${}^{53}\mathrm{Cr}$ metastable atoms are repumped from the magnetic trap and the large fermionic MOT is superimposed on the ${}^{52}\mathrm{Cr}$ MOT, we observe a decrease in the total number of ${}^{52}\mathrm{Cr}$ atoms. The solid line is the result of a fit, including interspecies losses.