change interaction. In a K-Rb- 21 Ne co-magnetometer which was used for rotation sensing, Rb atomic spins and the 21 Ne nuclear spins couple together by spin exchange. Due to the large Rb density and the Fermi contact constant of Rb- 21 Ne pair, the magnetization field of Rb atomic spins is much larger than that of the K in a K- 3 He co-magnetometer. At the co-magnetometer working point, the precession frequency of Rb atomic spins are much larger than that of the 21 Ne spins. The decay rate and precession frequency of 21 Ne atoms is much smaller than that of the point when the precession frequencies of the Rb and 21 Ne atoms are the same. In this experiment, the dynamics of the Rb- 21 Ne pair at different holding magnetic field point were studied. The frequency response of the co-magnetometer to oscillating magnetic field at different holding magnetic field point was also studied.
Abstract In a K-Rb- 21 Ne co-magnetometer, the Rb electron magnetic field which is experienced by the nuclear spin is about 100 times larger than that of the K in a K- 3 He co-magnetometer. The large electron magnetic field which is neglected in the K- 3 He co-magnetometer coupled Bloch equations model is considered here in the K-Rb- 21 Ne co-magnetometer to study the low frequency magnetic field suppression effect. Theoretical analysis and experimental results shows that in the K-Rb- 21 Ne spin co-magnetometer, not only the nuclear spin but also the large electron spin magnetic field compensate the external magnetic field noise. By comparison, only the 3 He nuclear spins mainly compensate the external magnetic field noise in a K- 3 He co-magnetometer. With this study, in addition to just increasing the magnetic field of the nuclear spins, we can suppress the magnetic field noise by increasing the density of the electron spin. We also studied how the magnetic field suppression effect relates to the scale factor of the K-Rb- 21 Ne co-magnetometer and we compared the scale factor with that of the K- 3 He co-magnetometer. Lastly, we show the sensitivity of our co-magnetometer. The magnetic field noise, the air density fluctuation noise and pumping power optimization are studied to improve the sensitivity of the co-magnetometer.
Abstract We report on the dynamics of spin-polarized Rb and 21 Ne ensembles in which the 21 Ne spin ensemble in a glass vapor cell experiences a high magnetic field produced by a Rb electron-spin ensemble. The coupled spin ensembles are modeled and the response of the transverse-step magnetic field excitation is solved and studied experimentally. Moreover, we analyze the frequency response of the ensembles to a transverse-oscillating magnetic field. We demonstrate the strong transverse damping and large frequency shift of the 21 Ne spin ensemble as the precession frequencies of 21 Ne spin and Rb spin match and the magnetic resonance spectroscopies of the two ensembles merge into one. We also demonstrate the operation of the spin ensembles as a self-compensating co-magnetometer that is insensitive to low-frequency magnetic fields that would be useful for rotation rate sensing. For such sensing applications, a large Rb density is achieved to polarize the 21 Ne spins. This density leads to a high Rb electron spin magnetic field and we demonstrate its effect on the dynamics of the co-magnetometer.
Abstract Searches for pseudo-magnetic spin couplings require implementation of techniques capable of sensitive detection of such interactions. While Spin-Exchange Relaxation Free (SERF) magnetometry is one of the most powerful approaches enabling the searches, it suffers from a strong magnetic coupling, deteriorating the pseudo-magnetic coupling sensitivity. To address this problem, here, we compare, via numerical simulations, the performance of SERF magnetometer and noble-gas-alkali-metal co-magnetometer, operating in a so-called self-compensating regime. We demonstrate that the co-magnetometer allows reduction of the sensitivity to low-frequency magnetic fields without loss of the sensitivity to nonmagnetic couplings. Based on that we investigate the responses of both systems to the oscillating and transient spin perturbations. Our simulations reveal about five orders of magnitude stronger response to the neutron pseudo-magnetic coupling and about three orders of magnitude stronger response to the proton pseudo-magnetic coupling of the co-magnetometer than those the SERF magnetometer. Different frequency responses of the co-magnetometer to magnetic and nonmagnetic perturbations enables differentiation between these two types of interactions. This outlines the ability to implement the co-magnetometer as an advanced sensor for the Global Network of Optical Magnetometer for Exotic Physics searches (GNOME), aiming at detection of ultra-light bosons (e.g., axion-like particles).
We have studied the polarization of the 85Rb and the fundamental sensitivity of two types of hybrid optical pumping spin exchange relaxation free (SERF) co-magnetometers based on 39K-85Rb-21Ne and 133Cs-85Rb-21Ne with taking the wall relaxation rate into account,which has a big effect on the polarization and fundamental sensitivity,but it is often neglected in the experiments,respectively.The polarization of the 85Rb varies with the thirteen systemic parameters: the number density of buffer gas 21Ne and quench gas N2,frequency rate of pump beam,cell temperature,the photon number flux,mole fraction of 85Rb,cell effective radius,pump beam spot radius,power density of pump beam,input rotation velocity in the x and y direction,external magnetic field in the y and z direction,respectively.The number density of the 21Ne,photon number flux,pump beam spot radius and frequency rate will affect the polarization of the 85Rb greatly by affecting the the pumping rate of pump beam,a magnetic field produced by 85Rb atom spins and experienced by the 21Ne spins.We obtain a general formula on the fundamental sensitivity of the hybrid optical pumping SERF co-magnetometers due to shot-noise,where the fundamental sensitivity varies with the twelve systemic parameters: the number density of buffer gas and quench gas,frequency rate of pump beam,photon number flux,mole fraction of 85Rb,cell effective radius,pump beam spot radius,power density of pump beam,external magnetic field,measurement volume,cell temperature and measurement time.The highest fundamental sensitivity
7.5878×10−11 rad/s/Hz1/2 of 133Cs-85Rb-21Ne co-magnetometer is higher than the ultimate theoretical sensitivity
2×10−10 rad/s/Hz1/2 of K-21Ne co-magnetometer.The fundamental sensitivity limit of the hybrid optical pumping SERF co-magnetometers is superior to
3.7334×10−12 rad/s/Hz1/2.
Abstract Atomic co-magnetometers can be utilized for high-precision angular velocity sensing or fundamental physics tests. The sensitivity of a co-magnetometer determines the angle random walk of an angular velocity sensor and the detection limit for a fundamental physics test. A high-sensitivity K-Rb-21Ne co-magnetometer, which is utilized for angular velocity sensing, is presented in this paper. A new type of spin relaxation of Rb atom spins, which can broaden the zero-field magnetic resonance lines of the co-magnetometer, is discovered. Further studies show that the spin relaxation of Rb atoms is caused by a high Rb electron magnetization field. With this discovery, the total relaxation rate of Rb atoms is optimized to improve the sensitivity of the co-magnetometer. Moreover, its sensitivity is optimized by suppressing various noises. Especially, to suppress laser-related noises, the co-magnetometer is designed such that the sensitive axis of the co-magnetometer can be fixed to the direction in which the projection input of the earth’s rotation is 0. This is called a rotating co-magnetometer. A magnetic field sensitivity of 1.0 fT/Hz−1/2@5 Hz, which is equal to an angular velocity sensitivity of 2.1 × 10−8 rad s−1 Hz−1/2@5 Hz, is demonstrated using a spherical vapour cell with a diameter of 14 mm.