Abstract
We demonstrate single-shot imaging and narrow-line cooling of individual alkaline earth atoms in optical tweezers; specifically, strontium-88 atoms trapped in $515.2~\text{nm}$ light. We achieve high-fidelity single-atom-resolved imaging by detecting photons from the broad singlet transition while cooling on the narrow intercombination line, and extend this technique to highly uniform two-dimensional arrays of $121$ tweezers. Cooling during imaging is based on a previously unobserved narrow-line Sisyphus mechanism, which we predict to be applicable in a wide variety of experimental situations. Further, we demonstrate optically resolved sideband cooling of a single atom close to the motional ground state of a tweezer. Precise determination of losses during imaging indicate that the branching ratio from $^1$P$_1$ to $^1$D$_2$ is more than a factor of two larger than commonly quoted, a discrepancy also predicted by our ab initio calculations. We also measure the differential polarizability of the intercombination line in a $515.2~\text{nm}$ tweezer and achieve a magic-trapping configuration by tuning the tweezer polarization from linear to elliptical. We present calculations, in agreement with our results, which predict a magic crossing for linear polarization at $520(2)~\text{nm}$ and a crossing independent of polarization at 500.65(50)nm. Our results pave the way for a wide range of novel experimental avenues based on individually controlled alkaline earth atoms in tweezers -- from fundamental experiments in atomic physics to quantum computing, simulation, and metrology implementations.
Highlights
Optical tweezers and related optical micropotential techniques (OTs) have matured into a powerful tool for quantum science experiments with individually controlled atoms, illustrated by a variety of recent results spanning quantum simulation with Rydberg atoms [1,2,3], entangling operations [4,5,6,7], bottom-up assembly of Hubbard models [8,9], and cavity QED implementations [10,11,12]
Of particular interest are alkaline-earth(like) atoms (AEAs), which offer important features, e.g., narrow and ultranarrow optical transitions, which have already had a strong impact in various scientific fields, ranging from quantum metrology [31,32,33] and simulation [34,35,36,37,38,39] to novel approaches for atomic and molecular control [40,41]
At least one atom remains in the tweezer after the magneto-optical trap (MOT) cloud is dispersed with a probability greater than 99.95%, which corresponds to a mean number of at least 7 atoms, assuming a Poisson distribution for the loading statistics
Summary
Optical tweezers and related optical micropotential techniques (OTs) have matured into a powerful tool for quantum science experiments with individually controlled atoms, illustrated by a variety of recent results spanning quantum simulation with Rydberg atoms [1,2,3], entangling operations [4,5,6,7], bottom-up assembly of Hubbard models [8,9], and cavity QED implementations [10,11,12]. In addition to resolved sideband cooling, we study a previously unobserved narrow-line Sisyphus cooling mechanism [45,46] that counteracts fluorescence recoil heating over a wide parameter regime Such single-atom experiments in OTs provide a new tool for determining several important atomic properties of strontium, which we compare to theoretical models.
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