<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mi>He</mml:mi> <mml:mprescripts/> <mml:none/> <mml:mn>3</mml:mn> </mml:mmultiscripts> </mml:math> absolute magnetometer at geomagnetic field

The high accuracy of the nuclear spin <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mi>g</a:mi> </a:math> factor provides a feasible way to construct absolute magnetometry. However, at geomagnetic field, the sensitivity and accuracy of the nuclear spin magnetometer are limited by the ratio of nuclear-spin polarization and the detection efficiency of low-frequency signal. We propose an absolute magnetometer scheme based on the nuclear spin of <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mmultiscripts> <b:mi mathvariant="normal">He</b:mi> <b:mprescripts/> <b:none/> <b:mn>3</b:mn> </b:mmultiscripts> </b:math> , demonstrating an order-of-magnitude improved sensitivity and onefold improved accuracy compared to a proton magnetometer for the current geomagnetic field standard. We present systematic estimations on the sources of errors within the <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mmultiscripts> <d:mi mathvariant="normal">He</d:mi> <d:mprescripts/> <d:none/> <d:mn>3</d:mn> </d:mmultiscripts> </d:math> magnetometer. Through adopting multipass-probe scheme and radio-frequency power stabilization, it is promising to further improve the accuracy of the <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"> <f:mmultiscripts> <f:mi mathvariant="normal">He</f:mi> <f:mprescripts/> <f:none/> <f:mn>3</f:mn> </f:mmultiscripts> </f:math> magnetometer to 100 ppb at geomagnetic field, paving the way to the next generation of geomagnetic field standard.