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arXiv:2506.19701

Narrow-line-mediated Sisyphus cooling in the $^{3}\mathrm{P}_{2}$ metastable state of strontium

Chun-Chia Chen, Ryoto Takeuchi, 翔一 岡場, Hidetoshi Katori

Published Jun 24, 2025• 0 citations
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Abstract

We demonstrate narrow-line-mediated Sisyphus cooling of magnetically trapped strontium (Sr) in the $5s5p\,^{3}\textrm{P}_{2}$ state. A 641 nm standing-wave, blue-detuned from the $5s4d\,^{3}\textrm{D}_{3}$$\,\rightarrow$ $\,5p4d\,^{3}\textrm{F}_{4}$ transition, creates a dissipative optical lattice in the $^{3}\textrm{D}_{3}$ state. By combining Doppler cooling and Sisyphus cooling on the $5s5p\,^{3}\textrm{P}_{2}$$\,\rightarrow$ $5s4d\,^{3}\textrm{D}_{3}$ transition at 2.92 $μ$m, we observed efficient cooling of magnetically trapped atoms. By optically pumping the atoms to the $5s5p\,^{3}\textrm{P}_{0}$ state, we facilitate continuous outcoupling via a moving optical lattice with two fold improvement in atom number. Our scheme applies to next-generation quantum sensors using continuous ultracold atomic beams.

DOI
10.48550/arxiv.2506.19701

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Narrow-line-mediated Sisyphus cooling in the 3P2^{3}\mathrm{P}_{2}3P2​ metastable state of strontium
We demonstrate narrow-line-mediated Sisyphus cooling of magnetically trapped strontium (Sr) in the 5s5p 3P25s5p\,^{3}\textrm{P}_{2}5s5p3P2​ state. A 641 nm standing-wave, blue-detuned from the 5s4d\,^{3}\textrm{D}_{3}$$\,\rightarrow  5p4d 3F4\,5p4d\,^{3}\textrm{F}_{4}5p4d3F4​ transition, creates a dissipative optical lattice in the 3D3^{3}\textrm{D}_{3}3D3​ state. By combining Doppler cooling and Sisyphus cooling on the 5s5p\,^{3}\textrm{P}_{2}$$\,\rightarrow 5s4d 3D35s4d\,^{3}\textrm{D}_{3}5s4d3D3​ transition at 2.92 μμμm, we observed efficient cooling of magnetically trapped atoms. By optically pumping the atoms to the 5s5p 3P05s5p\,^{3}\textrm{P}_{0}5s5p3P0​ state, we facilitate continuous outcoupling via a moving optical lattice with two fold improvement in atom number. Our scheme applies to next-generation quantum sensors using continuous ultracold atomic beams.
We demonstrate narrow-line-mediated Sisyphus cooling of magnetically trapped strontium (Sr) in the 5 s 5 p P 2 3 state. A 641 nm standing-wave, blue detuned from the 5 s 4 d D 3 3 → 5 p 4 d F 4 3 transition, creates a dissipative optical lattice in the D 3 3 state. By combining Doppler cooling and Sisyphus cooling on the 5 s 5 p P 2 3 → 5 s 4 d D 3 3 transition at 2.92 µ m , we observed efficient cooling of magnetically trapped atoms. By optically pumping the atoms to the 5 s 5 p P 0 3 state, we facilitate continuous outcoupling via a moving optical lattice with twofold improvement in atom number. Our scheme applies to next-generation quantum sensors using continuous ultracold atomic beams.
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Abstract We have demonstrated the continuous outcoupling of ultracold 88 Sr atoms using a moving optical lattice. While Sr atoms are Zeeman-slowed and magneto-optically trapped on the 1 S 0 – 1 P 1 transition, the atoms relaxed to the 5s5p 3 P 2 metastable state are magnetically trapped and Doppler cooled on the 5s5p 3 P 2 –5s4d 3 D 3 transition at 2.92 μ m. By optically pumping the atoms to the 5s5p 3 P 0 state, we outcouple the atoms by a moving optical lattice. Such a continuous atomic source enables superradiant lasers and the zero-dead-time operation of atom interferometers and optical lattice clocks.
We report three-stage laser cooling of Sr atoms using the 5s21S05{s}^{2}\phantom{\rule{0.16em}{0ex}}^{1}S_{0}5s21S0​ ground state and the 5s5p3P25s5p\phantom{\rule{0.16em}{0ex}}^{3}P_{2}5s5p3P2​ metastable state. 87Sr^{87}\mathrm{Sr}87Sr atoms are precooled in a magneto-optical trap simultaneously operated on the 5s21S05{s}^{2}\phantom{\rule{0.16em}{0ex}}^{1}S_{0}5s21S0​--5s5p1P15s5p\phantom{\rule{0.16em}{0ex}}^{1}P_{1}5s5p1P1​ transition at 461 nm and on the 5s5p3P25s5p\phantom{\rule{0.16em}{0ex}}^{3}P_{2}5s5p3P2​--5s5d3D35s5d\phantom{\rule{0.16em}{0ex}}^{3}D_{3}5s5d3D3​ transition at 496 nm. Atoms optically pumped to the 5s5p3P2(F=13/2)5s5p\phantom{\rule{0.16em}{0ex}}^{3}P_{2}(F=13/2)5s5p3P2​(F=13/2) state are magneto-optically trapped and cooled down to 2.5(2) $\ensuremath{\mu}\mathrm{K}$ on the 5s5p3P25s5p\phantom{\rule{0.16em}{0ex}}^{3}P_{2}5s5p3P2​--5s4d3D35s4d\phantom{\rule{0.16em}{0ex}}^{3}D_{3}5s4d3D3​ transition at $2.9\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$. Using this transition, we investigate one dimensional polarization gradient cooling of 88Sr^{88}\mathrm{Sr}88Sr atoms, which have simple energy levels without hyperfine structure, down to 0.22(18) $\ensuremath{\mu}\mathrm{K}$ or 17 times the recoil temperature. We discuss prospects for continuous generation of ultracold Sr atoms combined with a state transfer technique.
We report the magnetic trapping of metastable 3P2{}^{3}{P}_{2}3P2​ atomic strontium. Atoms are cooled in a magneto-optical trap (MOT) operating on the dipole-allowed ${}^{1}{S}_{0}{\ensuremath{-}}^{1}{P}_{1}$ transition at 461 nm. Decay via ${}^{1}{\stackrel{\ensuremath{\rightarrow}}{{P}_{1}}}^{1}{\stackrel{\ensuremath{\rightarrow}}{{D}_{2}}}^{3}{P}_{2}$ continuously loads a magnetic trap formed by the quadrupole magnetic field of the MOT. Over 108{10}^{8}108 atoms at a density of $8\ifmmode\times\else\texttimes\fi{}{10}^{9}{\mathrm{cm}}^{\ensuremath{-}3}$ and temperature of 1 mK are trapped. The atom temperature is significantly lower than what would be expected from the kinetic and potential energies of atoms as they are transferred from the MOT. This suggests the occurrence of thermalization and evaporative cooling in the magnetic trap.
We report a two-color magneto-optical trap that continuously operates on the (5s2) 1S0−(5s5p) 1P1\mathrm{(5s^2)\:^1S_0-(5s5p)\:^1P_1}(5s2)1S0​−(5s5p)1P1​ and (5s5p) 3P2−(5s5d) 3D3\mathrm{(5s5p)\:^3P_2-(5s5d)\:^3D_3}(5s5p)3P2​−(5s5d)3D3​ transitions in 88Sr\mathrm{^{88}Sr}88Sr. Owing to the sub-Doppler cooling from the metastable (5s5p) 3P2\mathrm{(5s5p)\:^3P_2}(5s5p)3P2​ state, a bimodal momentum distribution is observed, with the cold part of the ensemble reaching a temperature of 105 μ\mathrmμμK. A detailed simulation is established to explain the data. The absolute frequency of the (5s5p) 3P2−(5s5d) 3D3\mathrm{(5s5p)\:^3P_2-(5s5d)\:^3D_3}(5s5p)3P2​−(5s5d)3D3​ transition is measured to be 603 976 473 ±{\pm}± 2 MHz using a frequency comb, improving the literature value. The accompanying magnetic trap is characterized, and is shown to contribute to the sequential production of ensembles with temperatures down to 45 μ\mathrmμμK.