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1. 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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2. 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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3. 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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4. Hunt for magnetic signatures of hidden-photon and axion dark matter in the wilderness

   https://doi.org/10.1103/PhysRevD.108.096026  

   Sulai, Ibrahim A; Kalia, Saarik; Arza, Ariel; Bloch, Itay M; Muñoz, Eduardo Castro; Fabian, Christopher; Fedderke, Michael A; Forseth, Madison; Garthwaite, Brian; Graham, Peter W; et al (November 2023, Physical Review D)

   Earth can act as a transducer to convert ultralight bosonic dark matter (axions and hidden photons) into an oscillating magnetic field with a characteristic pattern across its surface. Here we describe the first results of a dedicated experiment, the Search for Noninteracting Particles Experimental Hunt, that aims to detect such dark-matter-induced magnetic-field patterns by performing correlated measurements with a network of magnetometers in relatively quiet magnetic environments (in the wilderness far from human-generated magnetic noise). Our experiment constrains parameter space describing hidden-photon and axion dark matter with Compton frequencies in the 0.5–5.0 Hz range. Limits on the kinetic-mixing parameter for hidden-photon dark matter represent the best experimental bounds to date in this frequency range. 

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5. An improved synthetic signal injection routine for the Haloscope At Yale Sensitive To Axion Cold dark matter (HAYSTAC)

   https://doi.org/10.1063/5.0137870  

   Zhu, Yuqi; Jewell, M. J.; Laffan, Claire; Bai, Xiran; Ghosh, Sumita; Graham, Eleanor; Cahn, S. B.; Maruyama, Reina H.; Lamoreaux, S. K. (May 2023, Review of Scientific Instruments)

   Microwave cavity haloscopes are among the most sensitive direct detection experiments searching for dark matter axions via their coupling to photons. When the power of the expected microwave signal due to axion–photon conversion is on the order of 10−24 W, having the ability to validate the detector response and analysis procedure by injecting realistic synthetic axion signals becomes helpful. Here, we present a method based on frequency hopping spread spectrum for synthesizing axion signals in a microwave cavity haloscope experiment. It allows us to generate a narrow and asymmetric shape in frequency space that mimics an axion’s spectral distribution, which is derived from a Maxwell–Boltzmann distribution. In addition, we show that the synthetic axion’s power can be calibrated with reference to the system noise. Compared to the synthetic axion injection in the Haloscope At Yale Sensitive to Axion Cold dark matter (HAYSTAC) Phase I, we demonstrated synthetic signal injection with a more realistic line shape and calibrated power. 

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