Spin exchange broadening of magnetic resonance lines in a high-sensitivity rotating K-Rb-21Ne co-magnetometer

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.

Analysis on the Magnetic Field Response for Nuclear Spin Co-Magnetometer Operated in Spin-Exchange Relaxation-Free Regime

“…A tabletop K-Rb- 21 Ne SERFCM was developed and used to verify the theoretical analysis. The schematic of the co-magnetometer is shown in Fig.1.…”

“…As the gyromagnetic ratio of a 21 Ne atom is much smaller than that of a 3 He atom or a 129 Xe atom, the fundamental rotation measurement sensitivity of a K-Rb- 21 Ne co-magnetometer is estimated to be higher than that of a K-3 He co-magnetometer or a Cs-129 Xe co-magnetometer at the same magnetic field noise level. Therefore, we have turned from Cs-129 Xe to K-Rb- 21 Ne. Although a better sensitivity of 2.1 × 10 −8 rad/s/Hz 1/2 has been achieved with various noises in the co-magnetometer suppressed [21], the low-frequency angle drift is only on par with that of Romalis group [13], [19].…”

“…In the next decade, much efforts were devoted to inertial rotation sensing theory analysis [16], dual-axis cross-talk decoupling scheme study [17], [18] and novel atom manipulation and interrogation methods validation [19], [20]. As the gyromagnetic ratio of a 21 Ne atom is much smaller than that of a 3 He atom or a 129 Xe atom, the fundamental rotation measurement sensitivity of a K-Rb- 21 Ne co-magnetometer is estimated to be higher than that of a K-3 He co-magnetometer or a Cs-129 Xe co-magnetometer at the same magnetic field noise level. Therefore, we have turned from Cs-129 Xe to K-Rb- 21 Ne.…”

“…Therefore, we have turned from Cs-129 Xe to K-Rb- 21 Ne. Although a better sensitivity of 2.1 × 10 −8 rad/s/Hz 1/2 has been achieved with various noises in the co-magnetometer suppressed [21], the low-frequency angle drift is only on par with that of Romalis group [13], [19]. The long-term stability of the co-magnetometer improved little even though we reduce it to tabletop instrument size with a volume of 350 mm × 350 mm × 280 mm to suppress the temperature induced drifts from optical components.…”

“…In this paper, the magnetic field response model of the SERFCM is derived based on state space method and the model is experimentally validated on a tabletop K-Rb- 21 Ne co-magnetometer. We find that the transfer function between the low frequency transverse magnetic field and system output can be characterized with first order differentiation element instead of differentiation element, which means that the nuclear magnetization can no longer be able to completely cancel the magnetic field fluctuations as supposed in previous works [13], [23].…”