[Paper Review] High-fidelity detection of large-scale atom arrays in an optical lattice

Renhao Tao, Maximilian Ammenwerth+3 more|arXiv (Cornell University)|Sep 9, 2023

Cold Atom Physics and Bose-Einstein Condensates4 citations

TL;DR

This paper demonstrates high-fidelity (99.9995(3)%) and high-survival (99.80(5)%) imaging of up to 399 strontium atoms in an optical lattice using repulsive Sisyphus cooling, enabling scalable, repeatable lattice-tweezer-lattice transfers and direct loading of over 10,000 atoms into a single-plane optical lattice for use as a reconfigurable, locally addressable reservoir in quantum simulation and computing platforms.

ABSTRACT

Recent advances in quantum simulation based on neutral atoms have largely benefited from high-resolution, single-atom sensitive imaging techniques. A variety of approaches have been developed to achieve such local detection of atoms in optical lattices or optical tweezers. For alkaline-earth and alkaline-earth-like atoms, the presence of narrow optical transitions opens up the possibility of performing novel types of Sisyphus cooling, where the cooling mechanism originates from the capability to spatially resolve the differential optical level shifts in the trap potential. Up to now, it has been an open question whether high-fidelity imaging could be achieved in a "repulsive Sisyphus" configuration, where the trap depth of the ground state exceeds that of the excited state involved in cooling. Here, we demonstrate high-fidelity ($99.971(1)\%$) and high-survival ($99.80(5)\%$) imaging of strontium atoms using repulsive Sisyphus cooling. We use an optical lattice as a pinning potential for atoms in a large-scale tweezer array with up to $399$ tweezers and show repeated, high-fidelity lattice-tweezer-lattice transfers. We furthermore demonstrate loading the lattice with approximately 10000 atoms directly from the MOT and scalable imaging over $>10000$ lattice sites with a combined survival probability and classification fidelity better than $99.2\%$. Our lattice thus serves as a locally addressable and sortable reservoir for continuous refilling of optical tweezer arrays in the future.

Motivation & Objective

• To achieve high-fidelity, low-loss detection of large-scale atom arrays in optical lattices using repulsive Sisyphus cooling, a regime previously unexplored for alkaline-earth atoms.
• To enable scalable, repeatable transfer of atoms between optical tweezers and optical lattices using a common lattice potential for pinning and readout.
• To demonstrate direct, high-density loading of over 10,000 atoms into a single plane of an optical lattice, creating a locally addressable reservoir for continuous refilling of optical tweezer arrays.
• To achieve sub-2.2% intensity inhomogeneity in optical tweezer arrays through spectroscopic feedback and phase optimization, ensuring uniform trapping for quantum control.

Proposed method

• Employed repulsive Sisyphus cooling on strontium atoms using the 1S₀–3P₁ transition at 689 nm, where the ground state has a deeper trap than the excited state, enabling high-fidelity imaging despite the repulsive nature of the cooling mechanism.
• Used a 1040 nm retro-reflected beam to form a 2D optical lattice with lattice spacings of 579(2) nm (x) and 1187(18) nm (y), providing a pinning potential for atoms in the tweezer array.
• Created a 399-site optical tweezer array using a spatial light modulator (SLM) at 520 nm, with precise alignment to the lattice via coordinate system calibration using fluorescence imaging and Gaussian fitting.
• Performed phase retrieval and amplitude equalization using a two-step Gerchberg–Saxton algorithm with spectroscopic feedback on differential light shifts to reduce intensity inhomogeneity below 2.2%.
• Calibrated diffraction efficiency of the SLM using a diagnostic camera and weighted the target tweezer amplitudes by 1/√η in the phase-retrieval algorithm to correct for non-uniformities.
• Verified lattice-tweezer commensurability by matching lattice and tweezer coordinate angles (θ_x^lat = -1.090(0)°, θ_x^tw = -1.0452(2)°) and spacing ratios (c_x^tw = 6a_x, c_y^tw = 3a_y).

Experimental results

Research questions

• RQ1 Can high-fidelity imaging be achieved in a repulsive Sisyphus cooling configuration, where the ground state is more deeply trapped than the excited state?
• RQ2 Is it possible to perform repeated, high-fidelity lattice-tweezer-lattice transfers using a common optical lattice potential for both pinning and detection?
• RQ3 Can over 10,000 atoms be directly loaded into a single plane of an optical lattice with sufficient homogeneity to serve as a reservoir for optical tweezer arrays?
• RQ4 To what extent can optical tweezer intensity inhomogeneity be reduced using spectroscopic feedback and iterative phase optimization?

Key findings

• Achieved single-shot imaging fidelity of 99.9995(3)% for strontium atoms in an optical lattice using repulsive Sisyphus cooling, demonstrating the feasibility of this regime for high-fidelity detection.
• Demonstrated high survival probability of 99.80(5)% during the imaging process, indicating minimal atomic loss or heating during detection.
• Successfully performed repeated lattice-tweezer-lattice transfers with high fidelity, enabling reusability of the lattice as a staging platform for atom arrays.
• Directly loaded more than 10,000 atoms into a single plane of the optical lattice, establishing a scalable, locally addressable reservoir for future tweezer array refilling.
• Reduced optical tweezer intensity inhomogeneity to below 2.2% after three iterations of spectroscopic feedback and amplitude equalization, enabling uniform trapping for quantum control.
• Achieved precise alignment between the optical lattice and tweezer arrays with coordinate angles matching to within 0.05° and spacing ratios consistent with design (c_x^tw = 6a_x, c_y^tw = 3a_y).