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arXiv:2006.05369 · Review of Scientific Instruments

Confinement of an alkaline-earth element in a grating magneto-optical trap

Ananya Sitaram, Peter K. Elgee, Gretchen K. Campbell, Nikolai N. Klimov, Stephen Eckel, Daniel S. Barker

Published Oct 1, 2020• 43 citations
arXivHTMLPDF

Abstract

We demonstrate a compact magneto-optical trap (MOT) of alkaline-earth atoms using a nanofabricated diffraction grating chip. A single input laser beam, resonant with the broad 1S0 → 1P1 transition of strontium, forms the MOT in combination with three diffracted beams from the grating chip and a magnetic field produced by permanent magnets. A differential pumping tube limits the effect of the heated, effusive source on the background pressure in the trapping region. The system has a total volume of around 2.4 l. With our setup, we have trapped up to 5 × 106 88Sr atoms at a temperature of ∼6 mK, and with a trap lifetime of ∼1 s. Our results will aid the effort to miniaturize quantum technologies based on alkaline-earth atoms.

DOI
10.1063/5.0019551

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Physical Review Applied•Sep 19, 2025•2 citations
We demonstrate a compact magneto-optical trap (MOT) of alkaline-earth atoms using a nanofabricated diffraction grating chip. A single input laser beam, resonant with the broad 1S0 → 1P1 transition of strontium, forms the MOT in combination with three diffracted beams from the grating chip and a magnetic field produced by permanent magnets. A differential pumping tube limits the effect of the heated, effusive source on the background pressure in the trapping region. The system has a total volume of around 2.4 l. With our setup, we have trapped up to 5 × 106 88Sr atoms at a temperature of ∼6 mK, and with a trap lifetime of ∼1 s. Our results will aid the effort to miniaturize quantum technologies based on alkaline-earth atoms.
We demonstrate for the first time the two-color cooling and trapping of alkaline-earth atoms in a grating magneto-optical trap (gMOT). The trap is formed by a single incident laser beam together with four secondary beams that are generated via diffraction from a nanostructured wafer. A grating structure for a gMOT operating with strontium atoms is optimized and fabricated. We trap 10610^6106 88^{88}88Sr atoms on the 1^11S0_00​ →\rightarrow→ 1^11P1_11​ transition at 461  nm461\;\mathrm{nm}461nm and transfer 25  %25\;\%25% of these atoms to the second cooling stage on the narrower 1^11S0_00​ →\rightarrow→ 3^33P1_11​ intercombination transition at 689  nm689\;\mathrm{nm}689nm, preparing a sample of 2.5×1052.5\times 10^52.5×105 atoms at 5  μ5\;μ5μK. These results demonstrate for the first time the applicability of the gMOT technology in conjunction with two widely differing wavelengths and enable the continued miniaturization of alkaline-earth based quantum technologies like optical atomic clocks.
We demonstrate the two-color cooling and trapping of alkaline-earth atoms in a grating magneto-optical trap (GMOT). The trap is formed by a single incident laser beam together with four secondary beams that are generated via diffraction from a nanostructured wafer. A grating structure for a GMOT operating with strontium atoms is optimized and fabricated. We trap 10688Sr{10}^{6}{\phantom{\rule{0.2em}{0ex}}}^{88}\mathrm{Sr}10688Sr atoms on the ${}^{1}{S}_{0}{\ensuremath{\rightarrow}}^{1}{P}_{1}$ transition at 461nm461\phantom{\rule{0.2em}{0ex}}\mathrm{nm}461nm and transfer 25% of these atoms to the second cooling stage on the narrower ${}^{1}{S}_{0}{\ensuremath{\rightarrow}}^{3}{P}_{1}$ intercombination transition at 689nm689\phantom{\rule{0.2em}{0ex}}\mathrm{nm}689nm, preparing a sample of $2.5\ifmmode\times\else\texttimes\fi{}{10}^{5}$ atoms at $5\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{K}$. These results demonstrate the applicability of the GMOT technology in conjunction with two widely differing wavelengths and enable the continued miniaturization of alkaline-earth-based quantum technologies like optical atomic clocks.
Quantum sensors, like optical lattice clocks, undergo a continuous development from lab-based towards mobile systems. A key aspect in the miniaturization of the experimental setups is the development of compact atom sources. Conventional atom sources for alkaline-earth-like elements consist of a high-power oven and a six-beam magneto-optical trap (MOT) inside of vacuum chamber with extensive flanges, viewports and electrical feedthroughs. Here we present a highly compact vacuum package utilizing key technologies for future quantum sensor systems: A chip-based low-power atomic oven, a planar grating MOT chip, and a miniaturized vacuum pump all held inside an additively manufactured titanium vacuum chamber, featuring custom-sized vacuum flanges. In this miniaturized setup, spanning a volume of only 750 ml, we trap up to 10510^5105 Sr atoms in a MOT, requiring an oven heating power below 1 W.
Compared with the conventional three-dimensional magneto-optical trap (3D MOT), the grating magneto-optical trap (GMOT) enables the cooling and trapping of atoms with only a single beam of light, thereby significantly reducing the overall volume of the device. Here, a grating chip with high diffraction efficiency is designed, and its parameters are optimized through simulations, which effectively suppresses the power of the zero-order diffracted light. Subsequently, the grating chip is fabricated and characterized, and using this chip, we successfully trap 1.7×106 atoms. The temperatures of the atomic cloud in the axial and radial directions are 5.6 mK and 17.0 mK, respectively. The successful implementation of the atom cooling and trapping experiment based on the diffraction grating provides important reference for the miniaturization of cold atom-based quantum sensors.
Abstract Diffraction gratings have simplified the optical implementation of magneto-optical traps (MOTs) to require only a single input beam, however reaching high atom number and fast loading has proven to be a challenge. We equipped an atom chip with a grating surface and paired it with a velocity-tunable 2D+-MOT as an atomic source to facilitate efficient loading together with magnetic trapping. Using uniform grating illumination, we magneto-optically trap 1.0 ( 1 ) × 10 9 atoms within one second, cool them to 14.1 ( 3 ) μ K , and transfer a quarter of them into the magnetic chip trap. This is a key step towards simple portable quantum sensors employing (ultra-)cold atoms.
We present a two-dimensional grating magneto-optical trap (2D gMOT) for strontium, which produces a slow atomic beam in a compact form factor. The strontium 2D gMOT, using permanent magnets with an atomic dispenser, cools and traps atoms along two dimensions in the diffraction plane of a grating chip using the 1 S 0 → 1 P 1 (blue) transition. The system is configured in such a way that the atoms emitted from the dispenser source do not degrade the diffraction efficiency of the grating for long-term stable use. The performance of the 2D gMOT is analyzed with plug and probe beams, where the atomic source achieves a flux of 2.1 × 10 8 atoms/s and mean velocity of 6.4 m/s for an input laser power of 75 mW. The velocity measurement allows for the precise characterization of atom-photon scattering properties, showing that the compact 2D gMOT is suitable for portable quantum devices such as atomic clocks, quantum sensors, and precision spectroscopy.