Recent advances in tabletop quantum sensor technology have enabled searches for nongravitational interactions of dark matter (DM). Traditional axion DM experiments rely on sharp resonance, resulting in extensive scanning time to cover a wide mass range. In this work, we present a broadband approach in an alkali- 21 Ne spin system. We identify two distinct hybrid spin-coupled regimes: a self-compensation regime at low frequencies and a hybrid spin resonance regime at higher frequencies. By utilizing these two distinct regimes, we significantly enhance the bandwidth of 21 Ne nuclear spin compared to conventional nuclear magnetic resonance, while maintaining competitive sensitivity. We present a comprehensive broadband search for axion-like DM, covering 5 orders of magnitude of Compton frequencies range within [ 10 − 2 , 10 3 ] Hz. We set new constraints on the axion DM interactions with neutrons and protons, accounting for the effects of DM stochasticity. For the axion–neutron coupling, our results reach a low value of | g ann | ⩽ 3 × 10 − 10 in the frequency range [ 2 × 10 − 2 , 4 ] Hz surpassing astrophysical limits and providing the strongest laboratory constraints in the [ 10 , 100 ] Hz range. For the axion-proton coupling, we offer the best terrestrial constraints for the frequency ranges [ 2 × 10 − 2 , 5 ] Hz and [ 16 , 7 × 10 2 ] Hz.

The search for axions sits at the intersection of solving critical problems in fundamental physics, including the strong C P problem in QCD, uncovering the nature of dark matter, and understanding the origin of the Universe’s matter-antimatter asymmetry. The measurement of axion mediated spin-dependent interactions offers a powerful approach for axion detection. However, it has long been restricted to regions outside the “axion window” due to a significant trade-off: the need to effectively suppress the magnetic leakage from highly polarized spin sources while simultaneously detecting subfemtotesla level exotic physics signals at sub-decimeter-scale distances. In this work, we report new experimental results on axion mediated exotic spin-spin interactions using an iron-shielded SmCo 5 spin source in combination with a specially designed self-compensation comagnetometer. Employing a composite shielding structure, we achieved a suppression of the magnetic field by up to 10 11 . This enabled us to establish new constraints on the coupling between electrons and neutrons, improving previous experimental limits by up to 10 000 times within the axion window. Furthermore, we also set the strongest constraints on the coupling between electrons and protons. The proposed method holds substantial potential not only for advancing the search for new physics beyond the standard model but also for enabling transformative applications in biological and chemical research.

Hybrid spin-exchange optical pumping is widely used in precision measurements and tests of fundamental physics. In these researches and applications, accurate measurement of the spin polarizations of hybrid alkali atoms and noble gas atoms has a significant role. Here we propose a novel method of measuring the spin polarizations of hybrid K-Rb and ²¹ Ne atoms simultaneously. We study the mixture of the slowing-down factors of hybrid alkali atoms due to spin-exchange interactions between hybrid alkali atoms, and the resonance-frequency shift of alkali atoms due to spin-exchange interactions with noble-gas atoms. We investigate the relationship between the hybrid resonance frequency and the polarizations. The spin polarizations of alkali atoms and noble-gas atoms have been measured based on this method, which is from 0.082 to 0.756 and from 0.018 to 0.124 with uncertainties smaller than 10.4 % and 12.7 % respectively. This method is promising for the applications requiring simultaneous and real-time measurement of the polarizations of alkali and noble-gas atoms, such as inertial sensors and tests of fundamental physics.

Optical rotation detection system (ORDS) utilizing quantum nondemolition measurement methods is widely applied in the field of quantum metrology and quantum information. However, the sensitivity of ORDS is limited by the uncertainty from optical-couple noise during the measurement of the atomic spin ensemble. In this study, we specifically analyze the mechanism of optical-couple noise caused by the fluctuations of probe light’s polarization in the modulated ORDS with a new model established to describe atomic spin precession in this particular condition. It is discovered that transverse electron-spin polarization errors are generated by the residual probe photon spin polarization in the ORDS, which results in extra coupling magnetic noise. In order to suppress this noise, a novel in-situ method is proposed that the resultant electron-spin errors are reduced by a specifically designed closed-loop system. The results are verified through the ORDS in a co-magnetometer. After zeroing the extra probe photon spin polarization, an angular sensitivity better than 1×10 ^-8 rad/Hz ^1/2 is achieved for frequencies higher than 5 Hz, demonstrating a probe background noise of 0.26 fT/Hz ^1/2 @14.5 Hz, approaching electronic noise and photon shot noise. With closed-loop control, the optical rotation bias instability is promoted by 4.2 times (from 107.9 to 25.7 μrad/h), and the angular noise of the ORDS is reduced by 2.4 times at 1-100 Hz. The measurement uncertainty of the realized ORDS nears the standard quantum limit, paving the road for long-term ultrasensitive measurements for new physics explorations.

As the measurement of multiple parameters in a spin-exchange relaxation-free (SERF) comagnetometer requires a long time and complex experimentation, we present a novel dynamic frequency response-based method for the accurate and rapid measurement of key parameters in a SERF comagnetometer. By testing the dynamic frequency response to a transverse oscillating magnetic field, we can obtain multiple parameters simultaneously and quickly without interrupting the operation of the comagnetometer. This method simultaneously measures the nuclear longitudinal relaxation rate and alkali metal number density within minutes, with uncertainties of less than 20.8% and 14.0%, respectively. The main error sources in the nuclear longitudinal relaxation rate and alkali metal number density are the spin-exchange rate constant and spin-exchange enhancement factor, respectively. In addition, the polarization of alkali metal and noble gas atoms can be obtained during the experimental process, and the fast measurement of these parameters is beneficial for applications requiring simultaneous and in situ measurement of spin ensemble performance.

Ultra-sensitive comagnetometers, which are designed to detect nuclear- and electron-spin-dependent interaction, have important applications ranging from basic research to inertial navigation systems (INSs). Unfortunately, electric heating, which is typically used in comagnetometers, introduces noise and instability because of the unavoidable generation of a modulated magnetic field. In this study, we investigate and introduce a K-Rb-²¹Ne comagnetometer that uses laser heating for the first time, when operated in the spin exchange relaxation free regime. The performance of the comagnetometer, which is equipped with both laser heating and electric heating, is investigated, and the two heating modes are compared. The temperature characteristics of the comagnetometer are studied theoretically and experimentally. By optimizing the operating temperature and power density of the pump-light, an equivalent rotation sensitivity of 2.5 × 10 − 7 rad⁻¹ s⁻¹ Hz 1 / 2 @1 Hz is achieved in laser heating mode. The improvement of laser-heating technology could prove essential to reduce electron relaxation and increase the low-frequency sensitivity of comagnetometers. Our results indicate that laser heating can make comagnetometers more suitable for applications in basic research (fifth forces, dark matter, etc), INSs, and other accurate measurements of electronic and nuclear precession.