Experiments with the Grating MOTs of Strontium

We report realization of a strontium grating magneto-optical trap (MOT) operating on the narrow, ¹S₀ → ³P₁ transition and implementation of sawtooth wave adiabatic passage (SWAP). Grating MOTs, which use a nanofabricated diffraction grating to greatly simplify the MOT optical layout, are a platform that can realize quantum technologies outside the laboratory. Cold-alkaline earth atoms are a central component of many quantum devices, such as clock atom interferometers and optical clocks. The ¹S₀ → ³P₁ transition grating MOT traps as many as 3×10^{6 88}Sr atoms and cools them to an average temperature of 3.7 μK. Using SWAP, we can roughly double the transfer efficiency from the first stage of cooling, a ¹S₀ → ¹P₁ transition grating MOT, to the ¹S₀ → ³P₁ MOT. Despite being able to capture on the order of 3×10^{6 87}Sr atoms in the ¹S₀ → ¹P₁ MOT, we have been unable to observe trapping in the ¹S₀ → ³P₁ grating MOT. We present rate equation and optical Bloch equation simulations of the ¹S₀ → ³P₁ grating MOT, which suggest that grating MOTs of ⁸⁷Sr will be extremely difficult to realize because traditional "stirring" schemes are ineffective. Our results show that chip-scale quantum devices using bosonic strontium are within reach on the grating MOT platform.