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1. Rotational magic conditions for ultracold molecules in the presence of Raman and Rayleigh scattering

   https://doi.org/10.1088/1367-2630/ad56bf  

   Kotochigova, Svetlana; Guan, Qingze; Tiesinga, Eite; Scarola, Vito; DeMarco, Brian; Gadway, Bryce (June 2024, New Journal of Physics)

   Abstract Molecules have vibrational, rotational, spin-orbit and hyperfine degrees of freedom or quantum states, each of which responds in a unique fashion to external electromagnetic radiation. The control over superpositions of these quantum states is key to coherent manipulation of molecules. For example, the better the coherence time the longer quantum simulations can last. The important quantity for controlling an ultracold molecule with laser light is its complex-valued molecular dynamic polarizability. Its real part determines the tweezer or trapping potential as felt by the molecule, while its imaginary part limits the coherence time. Here, our study shows that efficient trapping of a molecule in its vibrational ground state can be achieved by selecting a laser frequency with a detuning on the order of tens of GHz relative to an electric-dipole-forbidden molecular transition. Close proximity to this nearly forbidden transition allows to create a sufficiently deep trapping potential for multiple rotational states without sacrificing coherence times among these states from Raman and Rayleigh scattering. In fact, we demonstrate that magic trapping conditions for multiple rotational states of the ultracold²³Na⁸⁷Rb polar molecule can be created. 

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2. Theory of the line shape of the 1S–2S transition for magnetically trapped antihydrogen

   https://doi.org/10.1088/1361-6455/ac2c8a  

   Gustafson, R A; Robicheaux, F (September 2021, Journal of Physics B: Atomic, Molecular and Optical Physics)

   Abstract The physics that determines the line shape of the 1S–2S transition in magnetically trapped H ¯ is explored. Besides obtaining an understanding of the line shape, one goal is to replace the dependence on large scale simulations of H ¯ with a simpler integration over well defined functions. For limiting cases, analytic formulas are obtained. Example calculations are performed to illustrate the limits of simplifying assumptions. We also describe a χ 2 method for choosing experimental parameters that can lead to the most accurate determination of the transition frequency. 

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3. Investigation of the fine structure of antihydrogen

   https://doi.org/10.1038/s41586-020-2006-5  

   Ahmadi, M.; Alves, B. X.; Baker, C. J.; Bertsche, W.; Capra, A.; Carruth, C.; Cesar, C. L.; Charlton, M.; Cohen, S.; Collister, R.; et al (February 2020, Nature)

   At the historic Shelter Island Conference on the Foundations of Quantum Mechanics in 1947, Willis Lamb reported an unexpected feature in the fine structure of atomic hydrogen: a separation of the 2S1/2 and 2P1/2 states1. The observation of this separation, now known as the Lamb shift, marked an important event in the evolution of modern physics, inspiring others to develop the theory of quantum electrodynamics2–5. Quantum electrodynamics also describes antimatter, but it has only recently become possible to synthesize and trap atomic antimatter to probe its structure. Mirroring the historical development of quantum atomic physics in the twentieth century, modern measurements on anti-atoms represent a unique approach for testing quantum electrodynamics and the foundational symmetries of the standard model. Here we report measurements of the fine structure in the n = 2 states of antihydrogen, the antimatter counterpart of the hydrogen atom. Using optical excitation of the 1S–2P Lyman-α transitions in antihydrogen6, we determine their frequencies in a magnetic field of 1 tesla to a precision of 16 parts per billion. Assuming the standard Zeeman and hyperfine interactions, we infer the zero-field fine-structure splitting (2P1/2–2P3/2) in antihydrogen. The resulting value is consistent with the predictions of quantum electrodynamics to a precision of 2 per cent. Using our previously measured value of the 1S–2S transition frequency6,7, we find that the classic Lamb shift in antihydrogen (2S1/2–2P1/2 splitting at zero field) is consistent with theory at a level of 11 per cent. Our observations represent an important step towards precision measurements of the fine structure and the Lamb shift in the antihydrogen spectrum as tests of the charge– parity–time symmetry8 and towards the determination of other fundamental quantities, such as the antiproton charge radius9,10, in this antimatter system. 

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4. Optical dipole trapping of Holmium

   Yip, C.; Booth, D.; Zhou, H.; Collett, J.; Hostetter, J.; Saffman, M. (January 2018, 49th annual meeting of the APS division of Atomic, Molecular, & optical physics)

   Neutral Holmiums 128 ground hyperfi ne states, the most of any non-radioactive element, is a test bed for quantum con- trol of a very high dimensional Hilbert space, and offers a promising platform for quantum computing. Previously we have cooled Holmium atoms in a MOT on a 410.5 nm transition and characterized its Ry- dberg spectra. We report here on the first optical dipole trapping of Holmium with a 532 nm wavelength trap laser. The trap lifetime is close to 1 sec., limited by photon scattering from nearby transitions. The trapped atoms are used to measure the dynamic scalar and tensor polarizabilities which are compared with calculations based on measured oscillator strengths. We also report progress towards narrow line cooling and magnetic trapping of single atoms. 

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5. A Spectroscopic Study of the Insulator–Metal Transition in Liquid Hydrogen and Deuterium

   https://doi.org/10.1002/advs.201901668  

   Jiang, Shuqing; Holtgrewe, Nicholas; Geballe, Zachary_M; Lobanov, Sergey_S; Mahmood, Mohammad_F; McWilliams, R_Stewart; Goncharov, Alexander_F (November 2019, Advanced Science)

   Abstract The insulator‐to‐metal transition in dense fluid hydrogen is an essential phenomenon in the study of gas giant planetary interiors and the physical and chemical behavior of highly compressed condensed matter. Using direct fast laser spectroscopy techniques to probe hydrogen and deuterium precompressed in a diamond anvil cell and laser heated on microsecond timescales, an onset of metal‐like reflectance is observed in the visible spectral range atP>150 GPa andT≥ 3000 K. The reflectance increases rapidly with decreasing photon energy indicating free‐electron metallic behavior with a plasma edge in the visible spectral range at high temperatures. The reflectance spectra also suggest much longer electronic collision time (≥1 fs) than previously inferred, implying that metallic hydrogen at the conditions studied is not in the regime of saturated conductivity (Mott–Ioffe–Regel limit). The results confirm the existence of a semiconducting intermediate fluid hydrogen state en route to metallization. 

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