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arXiv:2102.11700 · Physical Review A

Narrow-line magneto-optical trap for europium

Yuki Miyazawa, Ryotaro Inoue, Hiroki Matsui, Kenta Takanashi, Mikio Kozuma

Published May 26, 2021• 18 citations
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Abstract

We report on the realization of a magneto-optical trap (MOT) for europium atoms using a narrow-line cooling transition with a natural linewidth of 97 kHz. Europium is a strongly dipolar species with interesting properties, such as the presence of hyperfine structure and the absence of electronic orbital angular momentum. Our starting point of the MOT is continuous capturing and cooling of optically pumped metastable europium atoms. We have employed simultaneous MOT for the metastable and ground-state atoms. The trapped metastable atoms are successively pumped back to the ground state and then continuously loaded to the narrow-line MOT, where up to $4.7\ifmmode\times\else\texttimes\fi{}{10}^{7}$ atoms are captured. A spin-polarized sample at a temperature of $6\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{K}$ and with a peak number density of $2.2\ifmmode\times\else\texttimes\fi{}{10}^{11}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ is obtained through the compression process, resulting in a phase space density of $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$.

DOI
10.1103/physreva.103.053122

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We report on the realization of a magneto-optical trap (MOT) for europium atoms using a narrow-line cooling transition with a natural linewidth of 97 kHz. Europium is a strongly dipolar species with interesting properties, such as the presence of hyperfine structure and the absence of electronic orbital angular momentum. Our starting point of the MOT is continuous capturing and cooling of optically pumped metastable europium atoms. We have employed simultaneous MOT for the metastable and ground-state atoms. The trapped metastable atoms are successively pumped back to the ground state and then continuously loaded to the narrow-line MOT, where up to 4.7\ifmmode×\else\texttimes\fi1074.7\ifmmode\times\else\texttimes\fi{}{10}^{7}4.7\ifmmode×\else\texttimes\fi107 atoms are captured. A spin-polarized sample at a temperature of 6\ensuremathμK6\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{K}6\ensuremathμK and with a peak number density of 2.2\ifmmode×\else\texttimes\fi1011cm\ensuremath−32.2\ifmmode\times\else\texttimes\fi{}{10}^{11}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}2.2\ifmmode×\else\texttimes\fi1011cm\ensuremath−3 is obtained through the compression process, resulting in a phase space density of 3\ifmmode×\else\texttimes\fi10\ensuremath−53\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}3\ifmmode×\else\texttimes\fi10\ensuremath−5.
We demonstrate laser cooling and magneto-optical trapping of europium. The atoms are optically pumped to a metastable state and then loaded from an atomic-beam source via conventional Zeeman slowing and magneto-optical trapping techniques using a $J=13/2\ensuremath{\leftrightarrow}J=15/2$ quasicyclic transition. The trapped populations contained up to $1\ifmmode\times\else\texttimes\fi{}{10}^{7}$ atoms, and a two-body loss rate is estimated as $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{3}/\mathrm{s}$ from the nonexponential loss of atoms at high densities. We also observed leakage out of the quasicyclic transition to the two metastable states with J=9/2J=9/2J=9/2 and 11/211/211/2, which is adequate to pump the laser-cooled atoms back to the J=7/2J=7/2J=7/2 ground state.
We report on the experimental realization of a robust and efficient magneto-optical trap for erbium atoms, based on a narrow cooling transition at 583 nm. We observe up to $N=2\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms at a temperature of about T=15T=15T=15 $\ensuremath{\mu}$K. This simple scheme provides better starting conditions for direct loading of dipole traps as compared to approaches based on the strong cooling transition alone, or on a combination of a strong and a narrow kHz transition. Our results on Er point to a general, simple, and efficient approach to laser cool samples of other lanthanide atoms (Ho, Dy, and Tm) for the production of quantum-degenerate samples.
Laser cooling on weak transitions is a useful technique for reaching ultracold temperatures in atoms with multiple valence electrons. However, for strongly magnetic atoms a conventional narrow-line magneto-optical trap (MOT) is destabilized by competition between optical and magnetic forces. We overcome this difficulty in Er by developing an unusual narrow-line MOT that balances optical and magnetic forces using laser light tuned to the blue side of a narrow (8 kHz) transition. The trap population is spin polarized with temperatures reaching below 2 muK. Our results constitute an alternative method for laser cooling on weak transitions, applicable to rare-earth-metal and metastable alkaline earth elements.
Laser cooling and magneto-optical trapping of neutral atoms has been a driving force in physics over the last few decades by providing an efficient method to produce cold and dense samples of cold atoms. Polar molecules which can have strong, long-range dipolar interactions and possess more rich internal structure promise a wide range of new physics and chemistry studies if they can be controlled efficiently. Until recently, the only way to achieve sub-milliKelvin level temperatures in molecules was to associate two precooled atomic species, which while very effective, has a firm bound on the chemical diversity accessible. While laser cooling of molecules relies on fortuitous molecular properties, it will significantly increase the choices of species available for molecular cooling.In this thesis I present the improved optical deceleration of the molecule yttrium monoxide (YO) and the loading of molecules into a 3-D magneto-optical trap (MOT). By making an improved choice of repumping scheme from our groups’ previous work, our photon scattering rate has been increased. By also improving our buffer gas cell source, we produce a much larger flux (2000 times higher) of slowed molecules at 5 m/s to reach the trapping region. I have designed and implemented 3-D MOT field coils operating at 5 MHz, and demonstrated a successful operation of a 3-D MOT. This is the first 3-D laser trapping of an oxide and the first of a molecule with an electronic state intermediate to the main cycling transition states.I have also performed a study of the transition from the ground state to the intermediate electronic state, which has a narrower linewidth of 150 kHz, in contrast to the main cycling transition’s linewidth of 5 MHz. This transition is well suited to second-stage narrow line cooling after loading molecules with the main MOT transition, which will allow direct laser cooling of a molecule to the 10 uK regime.
We realize narrow-linewidth magneto-optical traps of 46^{46}46Ti, 48^{48}48Ti and 50^{50}50Ti atoms based on a 1040 nm-wavelength transition, cooling atoms to a minimum temperature in one dimension of Tz=990(20)T_z=990(20)Tz​=990(20) nK and a three-dimensional temperature of T3D=1.28(7)T_\mathrm{3D}=1.28(7)T3D​=1.28(7) μμμK. Atoms are pre-cooled in a broad-line magneto-optical trap and then transferred with about 25% efficiency to the narrow-line trap. We operate the narrow-line trap in two stages over 85 ms. First, a single cooling beam, blue-detuned from the narrow-linewidth atomic resonance, optically pumps and traps the atoms on a two-dimensional surface where the Zeeman shift from the applied spherical quadrupole magnetic field brings the light nearly to resonance. Second, four additional beams, counter-propagating in the transverse directions, cool and compress the atoms in all dimensions. The high magnetic moment of the laser cooling state makes the dynamics of the narrow-line titanium trap similar to those of other magnetic atoms. We measure the lifetime of the excited state of the transition to be τ=8.2(9)τ=8.2(9)τ=8.2(9) μμμs, indicating a transition linewidth of γ/2π=20(2)γ/2π=20(2)γ/2π=20(2) kHz, and also measure isotope shifts on the narrow-line transition. We use Stern-Gerlach separation on the ultracold Ti gas to measure the mJm_JmJ​-distribution in the narrow-line magneto-optical trap, finding over 98% of the atoms in the stretched spin state.
We present our technique to create a magneto-optical trap (MOT) for dysprosium atoms using the narrow-line cooling transition at 626 nm to achieve suitable conditions for direct loading into an optical dipole trap. The MOT is loaded from an atomic beam via a Zeeman slower using the strongest atomic transition at 421 nm. With this combination of two cooling transitions we can trap up to 2.0·10(8) atoms at temperatures down to 6 μK. This cooling approach is simpler than present work with ultracold dysprosium and provides similar starting conditions for a transfer to an optical dipole trap.