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arXiv:2604.22406

Near-deterministic loading of optical tweezer arrays via repulsive barricade potentials

Archie C. Baldock, Alex J. Matthies, Luke Caldwell, H. J. Williams

Published Apr 24, 2026• 0 citations
arXivHTMLPDF

Abstract

Optical tweezers are a powerful tool for creating defect-free arrays of atoms and molecules, enabling advances in quantum simulation, computation, and precision metrology. However, the achievable array size is limited by the initial loading fraction, typically $50\,\%$ for atoms and $35\,\%$ for molecules. Here, we propose a general scheme for enabling multiple loading cycles by protecting trapped particles using a repulsive barrier. We show that collision-limited lifetimes of particles in protected tweezers can exceed one second, leading to filling fractions of over $80\%$ after four loading cycles. Combined with existing rearrangement techniques, this approach enables efficient unity filling of tweezer arrays and provides a scalable pathway towards larger quantum technology platforms.

DOI
10.48550/arxiv.2604.22406

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Optical tweezers are a powerful tool for creating defect-free arrays of atoms and molecules, enabling advances in quantum simulation, computation, and precision metrology. However, the achievable array size is limited by the initial loading fraction, typically 50 %50\,\%50% for atoms and 35 %35\,\%35% for molecules. Here, we propose a general scheme for enabling multiple loading cycles by protecting trapped particles using a repulsive barrier. We show that collision-limited lifetimes of particles in protected tweezers can exceed one second, leading to filling fractions of over 80%80\%80% after four loading cycles. Combined with existing rearrangement techniques, this approach enables efficient unity filling of tweezer arrays and provides a scalable pathway towards larger quantum technology platforms.
Neutral atoms and molecules trapped in optical tweezers have become a prevalent resource for quantum simulation, computation, and metrology. However, the maximum achievable system sizes of such arrays are often limited by the stochastic nature of loading into optical tweezers, with a typical loading probability of only 50%. Here we present a species-agnostic method for dark-state enhanced loading (DSEL) based on real-time feedback, long-lived shelving states, and iterated array reloading. We demonstrate this technique with a 95-tweezer array of ^{88}Sr atoms, achieving a maximum loading probability of 84.02(4)% and a maximum array size of 91 atoms in one dimension. Our protocol is complementary to, and compatible with, existing schemes for enhanced loading based on direct control over light-assisted collisions, and we predict it can enable close-to-unity filling for arrays of atoms or molecules.
Molecular tweezer arrays offer great prospects for quantum simulation, sensing, and computing, and would benefit from methods that enhance loading efficiency. Whereas light-assisted collisions underpin enhanced loading methods for atomic tweezer arrays, this approach cannot be directly extended to molecular arrays due to collisional loss. We show how this collisional loss can be suppressed by shelving molecules in rotationally or vibrationally excited states, so that a shelved molecule interacts with a newly loaded molecule through a repulsive van der Waals interaction. By introducing microwave assisted collisions, we show how to control the final states and the energy released in a collision between a pair of molecules. Following this controlled collision, one of the two molecules can be ejected, and we explore several strategies for ensuring deterministic ejection. Our schemes rely on currently available techniques for laser-coolable molecules, and we predict achievable filling fractions up to 96%, paving the way for scalable molecular arrays.
We propose to repeatedly load laser-cooled molecules into optical tweezers, and transfer them to storage states that are rotationally excited by two additional quanta. Collisional loss of molecules in these storage states is suppressed, and a dipolar blockade prevents the accumulation of more than one molecule. Applying three cycles loads tweezers with single molecules at an 80% success rate, limited by residual collisional loss. This improved loading efficiency reduces the time needed for rearrangement of tweezer arrays, which would otherwise limit the scalability of neutral molecule quantum computers.
We introduce a method for improved loading into a single-atom optical tweezer array, utilizing iterative loading with multiple reservoir tweezers. Demonstrated with dual-wavelength tweezer arrays of Sr 88 atoms, our approach achieves a 96 % loading rate after four reload cycles. This method can significantly enhance existing tweezer rearrangement protocols and reduce optical power consumption for target tweezer arrays, thereby enabling a larger number of atoms in a quantum logic device. Our approach has the potential for implementation with different atomic species and combination with other enhanced loading methods.
Ultracold molecules are becoming an increasingly important technology for quantum simulation, computation, and sensing, but their state preparation in large, low-entropy arrays remains a key challenge. We propose to deterministically load single molecules into optical tweezer arrays or lattices from either thermal or degenerate gases, with a high probability of occupying the tweezer's motional ground state. Strong repulsion between microwave-shielded molecules prevents multiparticle occupancy. Our proposal represents a robust scheme for deterministic single molecule preparation directly in the motional ground state with expected fidelities exceeding 99 percent for small trap volumes and highly polar species. This method can be scaled to thousands of traps limited by the reservoir molecule number, opening the door to large, low-entropy polar molecule arrays for quantum computation, quantum simulation, and precision measurement.
We demonstrate rapid loading of a small array of optical tweezers with a single ^{87}Rb atom per site. We find that loading efficiencies of up to 90% per tweezer are achievable in less than 170 ms for traps separated by more than 1.7 μm. Interestingly, we find the load efficiency is affected by nearby traps and present the efficiency as a function of the spacing between two optical tweezers. This enhanced loading, combined with subsequent rearranging of filled sites, will enable the study of quantum many-body systems via quantum gas assembly.