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arXiv:2507.12291 · Physical Review A

Chirped magneto-optical trap of molybdenum

Sai Naga Manoj Paladugu, Nickolas Pilgram, Stephen Eckel, Eric B. Norrgard

Published Nov 18, 2025• 1 citation
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Abstract

We have directly loaded a cryogenic beam of molybdenum atoms into a magneto-optical trap. By chirping the detuning of the trapping lasers, we were able to enhance the number of atoms loaded into the trap by more than a factor of 2. We optimize the trapped samples for atom number, temperature, and lifetime by varying the laser-cooling parameters. The laser-cooled molybdenum atoms are subsequently transferred to a magnetic trap where we achieve vacuum-limited lifetimes of 100 ms. Comparison of magneto-optical trap and magnetic trap lifetimes allow us to extract partial decay rates of the $z{\phantom{\rule{0.16em}{0ex}}}^{7}{P}_{4}^{\text{o}}\ensuremath{\rightarrow}a{\phantom{\rule{0.16em}{0ex}}}^{5}{D}_{4}$ and $z{\phantom{\rule{0.16em}{0ex}}}^{7}{P}_{4}^{\text{o}}\ensuremath{\rightarrow}a{\phantom{\rule{0.16em}{0ex}}}^{5}{D}_{3}$ transitions. We also provide measurements of the isotope shifts for the $a{\phantom{\rule{0.16em}{0ex}}}^{7}{S}_{3}\ensuremath{\rightarrow}z{\phantom{\rule{0.16em}{0ex}}}^{7}{P}_{4}^{\text{o}}$ transition with up to four times better precision than previously reported. Finally, we discuss the prospect of applying the chriped magneto-optical trap to produce laser-cooled samples of MgF.

DOI
10.1103/49lr-6slw

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We have directly loaded a cryogenic beam of molybdenum atoms into a magneto-optical trap. By chirping the detuning of the trapping lasers, we were able to enhance the number of atoms loaded into the trap by more than a factor of 2. We optimize the trapped samples for atom number, temperature, and lifetime by varying the laser-cooling parameters. The laser-cooled molybdenum atoms are subsequently transferred to a magnetic trap where we achieve vacuum-limited lifetimes of 100 ms. Comparison of magneto-optical trap and magnetic trap lifetimes allow us to extract partial decay rates of the z7P4o\ensuremath→a5D4z{\phantom{\rule{0.16em}{0ex}}}^{7}{P}_{4}^{\text{o}}\ensuremath{\rightarrow}a{\phantom{\rule{0.16em}{0ex}}}^{5}{D}_{4}z7P4o​\ensuremath→a5D4​ and z7P4o\ensuremath→a5D3z{\phantom{\rule{0.16em}{0ex}}}^{7}{P}_{4}^{\text{o}}\ensuremath{\rightarrow}a{\phantom{\rule{0.16em}{0ex}}}^{5}{D}_{3}z7P4o​\ensuremath→a5D3​ transitions. We also provide measurements of the isotope shifts for the a7S3\ensuremath→z7P4oa{\phantom{\rule{0.16em}{0ex}}}^{7}{S}_{3}\ensuremath{\rightarrow}z{\phantom{\rule{0.16em}{0ex}}}^{7}{P}_{4}^{\text{o}}a7S3​\ensuremath→z7P4o​ transition with up to four times better precision than previously reported. Finally, we discuss the prospect of applying the chriped magneto-optical trap to produce laser-cooled samples of MgF.
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 explore an efficient method for preparing large samples of ultracold calcium atoms. An optimized conventional (Doppler-limited) magneto-optical trap collects atoms from a Zeeman cooled atomic beam using a strong dipole transition within the singlet system. This transition is not completely closed thus yielding an intense flux of atoms into the metastable triplet state 3P2.{}^{3}{P}_{2}.3P2​. A second magneto-optical trap sharing the same magnetic-field gradient is superimposed which captures and further cools the metastables using the narrow-band infrared transition ${}^{3}{\stackrel{\ensuremath{\rightarrow}}{{P}_{2}}}^{3}{D}_{3}.$ In our present experiment we were able to prepare $3\ifmmode\times\else\texttimes\fi{}{10}^{8}$ atoms at temperatures below 20 microkelvin within 250 ms. Minor technical improvements of our setup promise to yield above 1010{10}^{10}1010 atoms at submicrokelvin temperatures within 1 s.
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We have magnetically trapped and evaporatively cooled atomic molybdenum. Using a cryogenic helium buffer gas, $2\ifmmode\times\else\texttimes\fi{}{10}^{10}$ molybdenum atoms are loaded into a magnetic trap at an initial temperature of 500 mK. The molybdenum atoms undergo two-body decay with a measured inelastic rate constant of ${g}_{\mathrm{in}}=(1.2\ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ for the initial conditions after loading. The molybdenum atoms are cooled by adiabatic expansion and forced evaporation to 200 mK.
We demonstrated laser cooling and trapping of thulium atoms at sub-Doppler temperatures in a magneto-optical trap (MOT). Up to 3 × 10 6 thulium atoms were trapped in the MOT at temperatures down to 25(5) μK which is approximately 10 times lower than the Doppler limit. The lifetime of atoms in the MOT varied between 0.3–1.5 s and was restricted mostly by optical leaks from the upper cooling level. The lower limit for the leaking rate was estimated to be 22(6) s −1 . Due to a big magnetic moment of Tm atoms, a part of them were trapped in a magnetic trap from the quadrupole field of the MOT. We observed about 3 × 10 4 purely magnetically trapped atoms at temperature of 25 μK with a lifetime in the trap of 0.5 s. Also we set up a “dark” MOT consisting of six crossed hollow beams which increased the number of trapped atoms by a factor of 5 leading to 1.5 × 10 7 atoms at the expense of higher temperature.
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