Alkaline earth atoms in optical tweezers

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.

Alkaline Earth Atoms in Optical Tweezers: A Detailed Exploration

The paper, "Alkaline Earth Atoms in Optical Tweezers," authored by Alexandre Cooper et al., presents a comprehensive study on the manipulation of strontium-88 ($\ce{^{88}Sr}$) atoms utilizing optical tweezers. This research explores the technical advancements in single-shot imaging and narrow-line cooling, primarily focusing on highly controlled atom arrays. The significant contributions of this work extend the capabilities of optical tweezer technology by integrating alkaline earth atoms (AEAs), broadening potential experimental applications and environments.

Key Results and Experimental Techniques

The authors achieve high-fidelity imaging of individual $\ce{^{88}Sr}$ atoms trapped in optical tweezers at $515.2~\text{nm}$ by leveraging broad singlet transition photon detection while simultaneous cooling on a narrow intercombination line. Central to this achievement is a novel narrow-line Sisyphus cooling mechanism, characterized by a previously unobserved behavior that shows promising application across diverse experimental setups. Notably, the calculated discrepancy in the branching ratio from $\ce{^{1}P_{1}}$ to $\ce{^{1}D_{2}}$—a critical parameter for loss determination during imaging—is found to be more than twice the conventional predictions, a result confirmed by theoretical ab initio calculations.

Impressively, the study details the fine-tuning of the optical tweezer configuration to achieve a "magic-trapping" state by altering the tweezer polarization. Through modification from linear to elliptical polarization, they determine the differential polarizability of the intercombination line, predicting compatibility with theoretical calculations. These findings underscore the precise control over tweezer arrays necessary to optimize trapping conditions for future experimentation.

Implications and Future Directions

The implications of this research are both far-reaching and profound. Practically, the work establishes a framework for utilizing AEAs in quantum computing, simulation, and metrology. The single-atom control and imaging fidelity demonstrated in this study are pivotal for the advancement of quantum simulation models requiring defect-free atomic arrays. The paper also sheds light on the potential for such systems in developing novel metrological instruments and standards, benefiting from the narrow-linewidth transitions inherent to AEAs.

Theoretical implications are equally significant. The new recoil-less Sisyphus mechanism opens up possibilities in cooling strategies beyond traditional parameters, potentially reducing system complexities required for achieving near-ground-state cooling. Moreover, the reevaluation of atomic properties such as branching ratios serves as a clarion call for further theoretical exploration, especially in improving the accuracy of atomic models.

The study suggests future exploration in various domains, including but not limited to, the interaction of AEAs with Rydberg states and cavity QED systems. Such interactions are crucial for quantum information processes where coherence and control are paramount. Additionally, the methodology presented could be adapted to other AEAs or even dipolar atoms, suggesting a versatile application across diverse atomic species. These prospects are particularly enticing for the development of highly precise quantum computing architectures leveraging the distinctive properties of AEAs.

In summary, the paper by Cooper et al. offers a detailed and methodical advancement in the control and application of alkaline earth atoms within optical tweezers. It serves as both a foundational and inspirational piece for ongoing research in quantum science, firmly setting the stage for subsequent breakthroughs in quantum technology applications.