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1. Search for monopole-dipole interactions with atom interferometry

   https://doi.org/10.1103/vmkt-97vl  

   Abe, Mahiro; Hogan, Jason M; Kaplan, David E; Overstreet, Chris; Rajendran, Surjeet (June 2025, Physical Review D)

   Light, weakly coupled bosonic particles such as axions can mediate long range monopole-dipole interactions between matter and spins. We propose a new experimental method to detect such a force exerted by the spin of electrons on a freely falling atom using atom interferometry. The intrinsic advantages of atom interferometry, such as the freely falling nature of the atom and the well-defined response of the atom to external magnetic fields, should enable the proposed method to overcome systematic effects induced by vibrations, magnetic fields, and gravity. This approach is most suited to probe forces with a range $\gtrsim 10\mathrm{cm}$. With current technology, our proposed setup could potentially extend probes of such forces by an order of magnitude beyond present laboratory limits. Published by the American Physical Society2025 

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2. Gravitational caustics in an atom laser

   https://doi.org/10.1038/s41467-021-27555-3  

   Mossman, M. E.; Bersano, T. M.; Forbes, Michael McNeil; Engels, P. (December 2021, Nature Communications)

   Abstract Typically discussed in the context of optics, caustics are envelopes of classical trajectories (rays) where the density of states diverges, resulting in pronounced observable features such as bright points, curves, and extended networks of patterns. Here, we generate caustics in the matter waves of an atom laser, providing a striking experimental example of catastrophe theory applied to atom optics in an accelerated (gravitational) reference frame. We showcase caustics formed by individual attractive and repulsive potentials, and present an example of a network generated by multiple potentials. Exploiting internal atomic states, we demonstrate fluid-flow tracing as another tool of this flexible experimental platform. The effective gravity experienced by the atoms can be tuned with magnetic gradients, forming caustics analogous to those produced by gravitational lensing. From a more applied point of view, atom optics affords perspectives for metrology, atom interferometry, and nanofabrication. Caustics in this context may lead to quantum innovations as they are an inherently robust way of manipulating matter waves. 

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3. Moiré excitons in defective van der Waals heterostructures

   https://doi.org/10.1073/pnas.2105468118  

   Guo, Hongli; Zhang, Xu; Lu, Gang (August 2021, Proceedings of the National Academy of Sciences)

   Excitons can be trapped by moiré potentials in van der Waals (vdW) heterostructures, forming ordered arrays of quantum dots. Excitons can also be trapped by defect potentials as single photon emitters. While the moiré and defect potentials in vdW heterostructures have been studied separately, their interplay remains largely unexplored. Here, we perform first-principles calculations to elucidate the interplay of the two potentials in determining the optoelectronic properties of twisted MoS 2 /WS 2 heterobilayers. The binding energy, charge density, localization, and hybridization of the moiré excitons can be modulated by the competition and cooperation of the two potentials. Their interplay can also be tuned by vertical electric fields, which can either de-trap the excitons or strongly localize them. One can further tailor the interplay of the two potentials via defect engineering to create one-dimensional exciton lattices with tunable orientations. Our work establishes defect engineering as a promising strategy to realize on-demand optoelectronic responses. 

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4. Efficient electromagnetic transducers for spin-wave devices

   https://doi.org/10.1038/s41598-021-97627-3  

   Connelly, David A.; Csaba, Gyorgy; Aquino, Hadrian Renaldo; Bernstein, Gary H.; Orlov, Alexei; Porod, Wolfgang; Chisum, Jonathan (December 2021, Scientific Reports)

   Abstract This paper presents a system-level efficiency analysis, a rapid design methodology, and a numerical demonstration of efficient sub-micron, spin-wave transducers in a microwave system. Applications such as Boolean spintronics, analog spin-wave-computing, and magnetic microwave circuits are expected to benefit from this analysis and design approach. These applications have the potential to provide a low-power, magnetic paradigm alternative to modern electronic systems, but they have been stymied by a limited understanding of the microwave, system-level design for spin-wave circuits. This paper proposes an end-to-end microwave/spin-wave system model that permits the use of classical microwave network analysis and matching theory towards analyzing and designing efficient transduction systems. This paper further compares magnetostatic-wave transducer theory to electromagnetic simulations and finds close agreement, indicating that the theory, despite simplifying assumptions, is useful for rapid yet accurate transducer design. It further suggests that the theory, when modified to include the exchange interaction, will also be useful to rapidly and accurately design transducers launching magnons at exchange wavelengths. Comparisons are made between microstrip and co-planar waveguide lines, which are expedient, narrowband, and low-efficiency transducers, and grating and meander lines that are capable of high-efficiency and wideband performance. The paper concludes that efficient microwave-to-spin-wave transducers are possible and presents a meander transducer design on YIG capable of launching $$\varvec{\lambda = 500}\,$$ λ = 500 nm spin waves with an efficiency of − 4.45 dB and a 3 dB-bandwidth of 134 MHz. 

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5. Site-dependent selection of atoms for homogeneous atom-cavity coupling

   https://doi.org/10.48550/arXiv.2104.01201  

   Wu, B.; Greve, G. P.; Luo, C.; Thompson, J.K. (October 2022, ArXivorg)

   We demonstrate a method to obtain homogeneous atom-cavity coupling by selecting and keeping 87Rb atoms that are near maximally coupled to the cavity's standing-wave mode. We select atoms by imposing an AC Stark shift on the ground state hyperfine microwave transition frequency with light injected into the cavity. We then induce a spin flip with microwaves that are resonant for atoms that are near maximally coupled to the cavity mode of interest, after which, we use radiation pressure forces to remove from the cavity all the atoms in the initial spin state. Achieving greater homogeneity in the atom-cavity coupling will potentially enhance entanglement generation, intracavity driving of atomic transitions, cavity-optomechanics, and quantum simulations. This approach can easily be extended to other atomic species with microwave or optical transitions. 

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