Among the prominent candidates for dark matter are bosonic fields with small scalar couplings to the Standard-Model particles. Several techniques are employed to search for such couplings and the current best constraints are derived from tests of gravity or atomic probes. In experiments employing atoms, observables would arise from expected dark-matter-induced oscillations in the fundamental constants of nature. These studies are primarily sensitive to underlying particle masses below 10 −14 eV. We present a method to search for fast oscillations of fundamental constants using atomic spectroscopy in cesium vapor. We demonstrate sensitivity to scalar interactions of dark matter associated with a particle mass in the range 8 · 10 −11 to 4 · 10 −7 eV. In this range our experiment yields constraints on such interactions, which within the framework of an astronomicalsize dark matter structure, are comparable with, or better than, those provided by experiments probing deviations from the law of gravity.
We demonstrate microwave-free eddy-current imaging using nitrogen-vacancy centers in diamond. By detecting the eddy-current induced magnetic field of conductive samples, we can distinguish between different materials and shapes and identify structural defects. Our technique allows for the discrimination of different materials according to their conductivity. The sensitivity of the measurements is calculated as 8×10 5 S/m √ Hz at 3.5 MHz, for a cylindrical sample with radius r 0 = 1 mm and height h = 0.1 mm (volume ∼ 0.3 mm 3 ), at a distance of 0.5 mm. In comparison with existing technologies, the diamond-based device exhibits a superior bandwidth and spatial resolution. In particular, we demonstrate a flat frequency response from DC to 3.5 MHz and a spatial resolution of 348 ± 2 µm.
We present a new cavity-based polarimetric scheme for highly sensitive and time-resolved measurements of birefringence and dichroism, linear and circular, that employs rapidly pulsed single-frequency continuous wave (CW) laser sources and extends current cavity-based spectropolarimetric techniques. We demonstrate how the use of a CW laser source allows for gains in spectral resolution, signal intensity, and data acquisition rate compared to traditional pulsed-based cavity ring-down polarimetry (CRDP). We discuss a particular CW-CRDP modality that is different from intensity-based cavity-enhanced polarimetric schemes as it relies on the determination of the polarization rotation frequency during a ring-down event generated by large intracavity polarization anisotropies. We present the principles of CW-CRDP and validate the applicability of this technique for the measurement of the non-resonant Faraday effect in solid SiO2 and CeF3 and gaseous butane. We give a general analysis of the fundamental sensitivity limits for CRDP techniques and show how the presented frequency-based methodology alleviates the requirement for high finesse cavities to achieve high polarimetric sensitivities and, thus, allows for the extension of cavity-based polarimetric schemes into different spectral regimes, but most importantly renders the CW-CRDP methodology particularly suitable for robust portable polarimetric instrumentations.
Light scalar dark matter (DM) with scalar couplings to matter is expected within several scenarios to induce variations in the fundamental constants of nature. Such variations can be searched for, among other ways, via atomic spectroscopy. Sensitive atomic observables arise primarily due to possible changes in the fine-structure constant or the electron mass. Most of the searches to date have focused on slow variations of the constants (i.e. modulation frequencies <1 Hz). In a recent experiment (2019 Phys. Rev. Lett. 123 141102) called weekend relaxion-search laboratory (WReSL), we reported on a direct search for rapid variations in the radio-frequency band. Such a search is particularly motivated within a class of relaxion DM models. We discuss the WReSL experiment, report on progress toward improved measurements of rapid fundamental constant variations, and discuss the planned extension of the work to molecules, in which rapid variations of the nuclear mass can be sensitively searched for.
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