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1. Frequency‐Scanning Considerations in Axionlike Dark Matter Spin‐Precession Experiments

   https://doi.org/10.1002/andp.202300223  

   Zhang, Yuzhe; Tumturk, Deniz Aybas; Bekker, Hendrik; Budker, Dmitry; Kimball, Derek F. Jackson; Sushkov, Alexander O.; Wickenbrock, Arne (November 2023, Annalen der Physik)

   Abstract Galactic dark matter may consist of axionlike particles (ALPs) that can be described as an “ultralight bosonic field” oscillating at the ALP Compton frequency. The ALP field can be searched for using nuclear magnetic resonance (NMR), where resonant precession of spins of a polarized sample can be sensitively detected. The ALP mass to which the experiment is sensitive is scanned by sweeping the bias magnetic field. The scanning either results in detection of ALP dark matter or rules out ALP dark matter with sufficiently strong couplings to nuclear spins over the range of ALP masses corresponding to the covered span of Larmor frequencies. In this work, scanning strategies are analyzed with the goal of optimizing the parameter‐space coverage via a proper choice of experimental parameters (e.g., the effective transverse relaxation time). 

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2. Constraints on bosonic dark matter from ultralow-field nuclear magnetic resonance

   https://doi.org/10.1126/sciadv.aax4539  

   Garcon, Antoine; Blanchard, John W.; Centers, Gary P.; Figueroa, Nataniel L.; Graham, Peter W.; Jackson Kimball, Derek F.; Rajendran, Surjeet; Sushkov, Alexander O.; Stadnik, Yevgeny V.; Wickenbrock, Arne; et al (October 2019, Science Advances)

   The nature of dark matter, the invisible substance making up over 80% of the matter in the universe, is one of the most fundamental mysteries of modern physics. Ultralight bosons such as axions, axion-like particles, or dark photons could make up most of the dark matter. Couplings between such bosons and nuclear spins may enable their direct detection via nuclear magnetic resonance (NMR) spectroscopy: As nuclear spins move through the galactic dark-matter halo, they couple to dark matter and behave as if they were in an oscillating magnetic field, generating a dark-matter–driven NMR signal. As part of the cosmic axion spin precession experiment (CASPEr), an NMR-based dark-matter search, we use ultralow-field NMR to probe the axion-fermion “wind” coupling and dark-photon couplings to nuclear spins. No dark matter signal was detected above background, establishing new experimental bounds for dark matter bosons with masses ranging from 1.8 × 10 −16 to 7.8 × 10 −14 eV. 

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3. Calibration of the Solid‐State Nuclear Magnetic Resonance Search for Axion‐Like Dark Matter

   https://doi.org/10.1002/andp.202300252  

   Winter, Andrew J.; Marić, Tanja; Balabanova, Viktoriya A.; Ádám, János; Randall, Glenn; Wickenbrock, Arne; Jackson Kimball, Derek F.; Budker, Dmitry; Sushkov, Alexander O. (November 2023, Annalen der Physik)

   Abstract Calibration of nuclear‐magnetic‐resonance‐based searches for axion‐like dark matter can be performed by free induction decay (FID) measurements. This manu‐ script describes FID experiments on several solid materials, motivated by the Cosmic Axion Spin Precession Experiment (CASPEr) program. Experiments with²⁰⁷Pb nuclear spins in ferroelectrics, lead magnesium niobate‐lead titanate (PbMg_1/3Nb_2/3O₃) (PbTiO₃)_1/3(PMN‐PT) and lead zirconium titante PbZr_0.52Ti_0.48O₃(PZT) are directly relevant to the CASPEr‐electric search for the electric dipole moment interaction of axion‐like dark matter. Experiments with³¹P nuclear spins in gadolinium‐doped hydroxypyromorphite Pb_4.95Gd_0.05(PO₄)₃OH (HPM:Gd) are used for apparatus calibration. The measurements characterized the nuclear spin ensemble coherence time and the magnetic resonance detection sensitivity for these samples. Calibration is performed using small tip‐angle pulses. 

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4. Source Mass Characterization in the ARIADNE Axion Experiment

   https://doi.org/10.1007/978-3-030-43761-9_9  

   Lohmeyer, C.; Aggarwal, N.; Arvanitaki, A.; Brown, A.; Fang, A.; Geraci, A.; Kapitulnik, A.; Kim, D.; Kim, Y; . Lee, I; et al (January 2020, Springer proceedings in physics)

   The Axion Resonant InterAction Detection Experiment (ARIADNE) is a collaborative effort to search for the QCD axion using nuclear magnetic resonance (NMR), where the axion acts as a mediator of spin-dependent forces between an unpolarized tungsten source mass and a sample of polarized helium-3 gas. Since the experiment involves precision measurement of a small magnetization, it relies on limiting ordinary magnetic noise with superconducting magnetic shielding. In addition to the shielding, proper characterization of the noise level from other sources is crucial.We investigate one such noise source in detail: the magnetic noise due to impurities and Johnson noise in the tungsten source mass. 

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5. A method for controlling the magnetic field near a superconducting boundary in the ARIADNE axion experiment

   https://doi.org/10.1088/2058-9565/abf1cc  

   Fosbinder-Elkins, H.; Kim, Y.; Dargert, J.; Harkness, M.; Geraci, A. A.; Levenson-Falk, E.; Mumford, S.; Fang, A.; Kapitulnik, A.; Matlashov, A.; et al (January 2022, Quantum Science and Technology)

   Abstract The QCD axion is a particle postulated to exist since the 1970s to explain the strong-CP problem in particle physics. It could also account for all of the observed dark matter in the Universe. The axion resonant interaction detection experiment (ARIADNE) intends to detect the QCD axion by sensing the fictitious ‘magnetic field’ created by its coupling to spin. Short-range axion-mediated interactions can occur between a sample of laser-polarized³He nuclear spins and an unpolarized source-mass sprocket. The experiment must be sensitive to magnetic fields below the 10⁻¹⁹T level to achieve its design sensitivity, necessitating tight control of the experiment’s magnetic environment. We describe a method for controlling three aspects of that environment which would otherwise limit the experimental sensitivity. Firstly, a system of superconducting magnetic shielding is described to screen ordinary magnetic noise from the sample volume at the 10⁸level, which should be sufficient to reduce the contribution of Johnson noise in the sprocket-shaped source mass, expected to be at the 10⁻¹²T $/\sqrt{\mathrm{H}\mathrm{z}}$level, to below the threshold for signal detection. Secondly, a method for reducing magnetic field gradients within the sample up to 10²times is described, using a simple and cost-effective design geometry. Thirdly, a novel coil design is introduced which allows the generation of fields similar to those produced by Helmholtz coils in regions directly abutting superconducting boundaries. This method allows the nuclear Larmor frequency of the sample to be tuned to match the axion field modulation frequency set by the sprocket rotation. Finally, we experimentally investigate the magnetic shielding factor of sputtered thin-film superconducting niobium on quartz substrates for various geometries and film thicknesses relevant for the ARIADNE axion experiment using SQUID magnetometry. The methods may be generally useful for magnetic field control near superconducting boundaries in other experiments where similar considerations apply. 

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