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1. An efficient 2D array of blue-detuned optical traps

   Graham, Trent; Xiaoyu, Jiang; Poole, Cody; Sun, Yuan; Lichtman, Martin; Saffman, Mark (May 2018, Bulletin American Physical Society, DAMOP 2018)

   We demonstrate a 2D lattice of blue-detuned optical traps which uses laser power efficiently, is tolerant to perturbations in beam alignment, and is insensitive to interferometric phases. Blue traps have several advantages over red traps despite requir- ing a more complicated beam geometry. Since atoms in a blue trap sit at an intensity minimum, Stark shift noise and site-to-site calibrations are minimized. However, constructing a blue lattice which efficiently con- verts laser power into trap depth, is challenging. For example, a lattice of bottle beams is inefficient because neighboring sites are separated by two walls, limiting the number of traps that can be formed. An array of tightly spaced Gaussian beams is a more efficient blue trap, but the trap potentials are susceptible to alignment perturbations. We demonstrate an array which uses diffractive optical elements to create a cross-hatched pattern of lines in the focal region where the atoms are trapped in up to 121 sites. This "line array" is almost twice as efficient as the Gaussian beam array and is more resilient to perturbations in beam alignment. 

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2. Integrating planar photonics for multi-beam generation and atomic clock packaging on chip

   https://doi.org/10.1038/s41377-023-01081-x  

   Ropp, Chad; Zhu, Wenqi; Yulaev, Alexander; Westly, Daron; Simelgor, Gregory; Rakholia, Akash; Lunden, William; Sheredy, Dan; Boyd, Martin M.; Papp, Scott; et al (December 2023, Light: Science & Applications)

   Abstract The commercialization of atomic technologies requires replacing laboratory-scale laser setups with compact and manufacturable optical platforms. Complex arrangements of free-space beams can be generated on chip through a combination of integrated photonics and metasurface optics. In this work, we combine these two technologies using flip-chip bonding and demonstrate an integrated optical architecture for realizing a compact strontium atomic clock. Our planar design includes twelve beams in two co-aligned magneto-optical traps. These beams are directed above the chip to intersect at a central location with diameters as large as 1 cm. Our design also includes two co-propagating beams at lattice and clock wavelengths. These beams emit collinearly and vertically to probe the center of the magneto-optical trap, where they will have diameters of ≈100 µm. With these devices we demonstrate that our integrated photonic platform is scalable to an arbitrary number of beams, each with different wavelengths, geometries, and polarizations. 

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3. Tunable optical traps over nonreciprocal surfaces

   https://doi.org/10.1364/OE.476269  

   Paul, N. K.; Gomez-Diaz, J. S. (January 2022, Optics Express)

   We propose engineering optical traps over plasmonic surfaces and precisely controlling the trap position with an external bias by inducing in-plane nonreciprocity on the surface. The platform employs an incident Gaussian beam to polarize targeted nanoparticles, and exploits the interplay between nonreciprocal and spin-orbit lateral recoil forces to construct stable optical traps and manipulate their position within the surface. To model this process, we develop a theoretical framework based on the Lorentz force combined with nonreciprocal Green’s functions and apply it to calculate the trapping potential. Rooted on this formalism, we explore the exciting possibilities offered by graphene to engineer stable optical traps using low-power laser beams in the mid-IR and to manipulate the trap position in a continuous manner by applying a longitudinal drift bias. Nonreciprocal metasurfaces may open new possibilities to trap, assemble and manipulate nanoparticles and overcome many challenges faced by conventional optical tweezers while dealing with nanoscale objects. 

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4. Self-aligning recirculated crossed optical dipole trap for lithium atoms

   https://doi.org/10.1103/PhysRevA.110.063121  

   Lian, Ming; Mrozek-McCourt, Maximillian; Angyal, Christopher K; Shaddel, Dadbeh; Blogg, Zachary J; Griffin, John R; Crawley, Ian; Sommer, Ariel T (December 2024, Physical Review A)

   Crossed optical dipole traps (ODTs) provide three-dimensional confinement of cold atoms and other optically trappable particles. However, the need to maintain the intersection of the two trapping beams poses strict requirements on alignment stability and limits the ability to move the trap. Here we demonstrate a crossed ODT design that features inherent stability of the beam crossing, allowing the trap to move and remain aligned. The trap consists of a single high-power laser beam, imaged back onto itself at an angle to form a crossed trap. Self-aligning behavior results from employing an imaging system with positive magnification tuned precisely to unity. We employ laser-cooled samples of lithium-6 atoms to demonstrate that the trap remains well aligned over a 4.3-mm travel range along an axis approximately perpendicular to the plane containing the crossed beams. Our scheme can be applied to bring an atomic cloud held in a crossed ODT close to a surface or field source for various applications in quantum simulation, sensing, and information processing. 

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5. Interleaved dual-species arrays of single atoms using a passive optical element and one trapping laser

   https://doi.org/10.1126/sciadv.adw4166  

   Fang, Chengyu; Miles, Jared; Goldwin, Jonathan; Lichtman, Martin; Gillette, Matthew; Bergdolt, Michael; Deshpande, Sanket; Norrell, Sam A; Huft, Preston; Kats, Mikhail A; et al (July 2025, Science Advances)

   We demonstrate trapping of individual rubidium (Rb) and cesium (Cs) atoms in an interleaved array of bright tweezers and dark bottle-beam traps, using a microfabricated optical element illuminated by a single-laser beam and a 4fsystem with spatial filtering. Our approach exploits the opposite-sign dynamic polarizabilities of Rb and Cs, ensuring that each species is exclusively trapped in either bright or dark sites. The passive optical mask creates optimal trap depths for both species using three transmittance levels while minimizing the optical phase difference, implemented using a variable-thickness absorbing layer of amorphous germanium. This trapping architecture achieves atom loading rates close to 50% while reducing system complexity compared to conventional methods using active optoelectronic components and/or multiple-laser wavelengths. 

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