Superconducting quantum magnetometer for magnetic relaxation measurements

B. V. Vasiliev, V. G. Grebinnik, V. G. Simkin

Qingqian Guo, Tao Hu, Chun-qiao Chen +6 more

Spin-exchange relaxation-free (SERF) atomic magnetometers are the promising non-cryogenic sensors to potentially replace the superconducting quantum interference device (SQUID) in the ultra-weak magnetic-field measurements. Although the SERF magnetometers have achieved a sensitivity of sub-femtotesla, the bandwidth is limited at a narrow range. In this work, we developed a closed-loop SERF magnetometer under proportional-integral (PI) control, the bandwidth could be adaptively tuned and extended above 1.2 kHz. A nearly 40-fold enhancement of the typical bandwidth was achieved in comparison with the open-loop system and the sensitivity was maintained at 15 fT/Hz1/2from 30 Hz to 750 Hz. Moreover, the magnetic field dynamic range could also be greatly improved. This proposed atomic magnetometer with higher bandwidth, sensitivity, and dynamic range has a good prospect in developing a compact, portable, and non-cryogenic magnetic field sensor and may find more applications in biomedical, nuclear magnetic resonance, and fundamental physics research.

N. V. Zavaritskiǐ, Михаил Семенович Легкоступов

Lijun Liu, Shuming Cheng, Bo Qi +2 more

Ultra sensitive detection and high precision measurement of magnetic fields have been of great importance for both fundamental physics and practical applications. Recent developments in the technology of atomic magnetometers have enabled the spin-exchange relaxation free (SERF) atomic magnetometers as the most sensitive devices for detecting and measuring static or quasi-static magnetic fields. In this paper, we analyze the effect of the most prominent relaxation mechanism (i.e., the spin-destruction collisions) on the precision of SERF magnetometers. For static magnetic fields, it is explicitly demonstrated how the spin-destruction collisions degrade the precision of the SERF magnetometers from the Heisenberg limit to the standard limit even with quantum resources being employed.

N. V. Zavaritskiǐ, Legkostupov

Huanyu Zhou, Yi Zhangu, Jin Liu +3 more

The deterioration of spin coherence has been a significant challenge in the field of quantum magnetic measurements based on optically pumped atomic magnetometers (OPAMs). However, measurement and evaluation methods for specific relaxation components of OPAMs under working conditions remain lacking, which impedes further improvement in OPAM performance. To address this, we propose a methodology for quantifying the relaxation components of an OPAM under realistic operating conditions. Using this method, we confirm the existence of an anomalous relaxation mechanism induced by radio-frequency (RF) magnetic fields and develop an empirical expression to describe its behavior. The results experimentally demonstrate that, in addition to the well-known spin-exchange relaxation, the dominant contributions to spin relaxation arise from optical pumping and RF magnetic fields. This work paves the way for sensitivity enhancement in quantum magnetometry and refines the theoretical understanding of relaxation mechanisms in OPAMs.