Narrow-line imaging of single strontium atoms in shallow optical tweezers

Single strontium atoms held in optical tweezers have so far only been imaged using the

broad ¹S₀ - ¹P₁ transition. For Yb, use of the narrow (183 kHz-wide) ¹S₀ - ³P₁ transition

for simultaneous imaging and cooling has been demonstrated in tweezers with a magic

wavelength for the imaging transition. We demonstrate high-fidelity imaging of sin-

gle Sr atoms using its even narrower (7.4 kHz-wide) ¹S₀ - ³P₁ transition. The atoms are

trapped in non-magic-wavelength tweezers. We detect the photons scattered during

Sisyphus cooling, thus keeping the atoms near the motional ground state of the tweezer

throughout imaging. The fidelity of detection is 0.9991(4) with a survival probability exceeding

0.99. An atom in a tweezer can be held under imaging conditions for 79(3) seconds

allowing for hundreds of images to be taken, limited mainly by background gas colli-

sions. The use of a fully closed (cycling) transition for imaging will provide a useful

tool for state specific detection. We detect atoms in an array of 36 tweezers with 813.4-

nm light and trap depths of 135(20) μK. This trap depth is three times shallower than

typically used for imaging on the broad ¹S₀ - ¹P₁ transition. Narrow-line imaging opens

the possibility to even further reduce this trap depth, as long as all trap frequencies are

kept larger than the imaging transition linewidth. Imaging using a narrow-linewidth

transition in a non-magic-wavelength tweezer also allows for selective imaging of a

given tweezer. As a demonstration, we selectively image (hide) a single tweezer from

the array. This provides a useful tool for quantum error correction protocols.