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.

We report the results of a search for axionlike dark matter using nuclear magnetic resonance (NMR) techniques. This search is part of the multi-faceted Cosmic Axion Spin Precession Experiment (CASPEr) program. In order to distinguish axionlike dark matter from magnetic fields, we employ a comagnetometry scheme measuring ultralow-field NMR signals involving two different nuclei ( 13 C and 1 H) in a liquid-state sample of acetonitrile-2-13 C ( 13 CH3CN). No axionlike dark matter signal was detected above background. This result constrains the parameter space describing the coupling of the gradient of the axionlike dark matter field to nucleons to be gaNN < 6 × 10 −5 GeV −1 (95% confidence level) for particle masses ranging from 10 −22 eV to 1.3 × 10 −17 eV, improving over previous laboratory limits for masses below 10 −21 eV. The result also constrains the coupling of nuclear spins to the gradient of the square of the axionlike dark matter field, improving over astrophysical limits by orders of magnitude over the entire range of particle masses probed.

We use magnetic-field-dependent features in the photoluminescence of negatively charged nitrogen-vacancy centers to measure magnetic fields without the use of microwaves. In particular, we present a magnetometer based on the level anti-crossing in the triplet ground state at 102.4 mT with a demonstrated noise floor of 6 nT/$\sqrt{\text{Hz}}$, limited by the intensity noise of the laser and the performance of the background-field power supply. The technique presented here can be useful in applications where the sensor is placed closed to conductive materials, e.g. magnetic induction tomography or magnetic field mapping, and in remote-sensing applications since principally no electrical access is needed.Comment: 5 pages, 4 figure

International audienceWe present a highly sensitive miniaturized cavity-enhanced room-temperature magnetic-field sensor based on nitrogen-vacancy centers in diamond. The magnetic resonance signal is detected by probing absorption on the 1042-nm spin-singlet transition. To improve the absorptive signal the diamond is placed in an optical resonator. The device has a magnetic-field sensitivity of 28  pT/Hz, a projected photon shot-noise-limited sensitivity of 22  pT/Hz, and an estimated quantum projection-noise-limited sensitivity of 0.43  pT/Hz with the sensing volume of ∼390  μm×4500  μm2. The presented miniaturized device is the basis for an endoscopic magnetic-field sensor for biomedical applications