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Physical Review Research

Narrow-line-mediated Sisyphus cooling in the P 2 3 metastable state of strontium

Chun-Chia Chen, Ryoto Takeuchi, Shoichi Okaba, Hidetoshi Katori

Published May 12, 2025• 3 citations
Publisher

Abstract

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.

DOI
10.1103/b26p-12j4

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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•May 15, 1998•8 citations
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.
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 3D35s4d\,^{3}\textrm{D}_{3}5s4d3D3​ →\,\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 3P25s5p\,^{3}\textrm{P}_{2}5s5p3P2​ →\,\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.
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 demonstrate subrecoil Sisyphus cooling using the long-lived ^{3}P_{0} clock state in alkaline-earth-like ytterbium. A 1388-nm optical standing wave nearly resonant with the ^{3}P_{0}→^{3}D_{1} transition creates a spatially periodic light shift of the ^{3}P_{0} clock state. Following excitation on the ultranarrow clock transition, we observe Sisyphus cooling in this potential, as the light shift is correlated with excitation to ^{3}D_{1} and subsequent spontaneous decay to the ^{1}S_{0} ground state. We observe that cooling enhances the loading efficiency of atoms into a 759-nm magic-wavelength one-dimensional (1D) optical lattice, as compared to standard Doppler cooling on the ^{1}S_{0}→^{3}P_{1} transition. Sisyphus cooling yields temperatures below 200 nK in the weakly confined, transverse dimensions of the 1D optical lattice. These lower temperatures improve optical lattice clocks by facilitating the use of shallow lattices with reduced light shifts while retaining large atom numbers to reduce the quantum projection noise. This Sisyphus cooling can be pulsed or continuous and is applicable to a range of quantum metrology applications.
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.
Optical lattice clocks have demonstrated unprecedented performance below the 10^-18 fractional level, advancing towards new standards of timekeeping and sensitive probes in fundamental physics. To further advance optical lattice clocks performance, it is crucial to attain lower temperatures which facilitates the use of shallow lattices with reduced light shifts, while retaining large atom numbers to reduce the quantum projection noise. Here, we present Sisyphus cooling using the long-lived 3P0 clock state in alkaline-earth-like ytterbium. Upon excitation on the ultranarrow clock transition, Sisyphus cooling is observed within a spatially periodic potential induced by a 1388-nm optical standing wave that is nearly resonant with the 3P0 → 3D1 transition. Our cooling demonstrates versatility, working both in free space and in a magic-wavelength lattice. It offers the flexibility of being employed in either pulsed or continuous modes, making it suitable to a range of quantum metrology applications.
In a ceramic vapor cell we have created a robust Sr magneto- optical trap that stores about 108 atoms with lifetimes > 200 ms. We eliminate the 5p 1P1 yields 4d1D2 yields 5p 3P2 leak and achieve a 10-fold improvement in trap lifetime by re-pumping the 5p 3P0,2 dark states with 679 nm and 707 nm light. The observed lifetime is now limited by cold collision losses, and we have preliminary measurements of the 2-body loss rate. Direct readout of the trap velocity distribution is possible using the narrow 5s2 1S0 yields 5p 3P1 intercombination line at 689 nm. We can also cool with this narrow transition and have achieved a 40-fold 1D velocity compression for about 5 percent of the trapped atoms by applying this second-stage cooling.