Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Precise Measurement of Magnetic Field Gradients from Free Spin
  Precession Signals of $^{3}$He and $^{129}$Xe Magnetometers   We report on precise measurements of magnetic field gradients extracted from
transverse relaxation rates of precessing spin samples. The experimental
approach is based on the free precession of gaseous, nuclear spin polarized
$^3$He and $^{129}$Xe atoms in a spherical cell inside a magnetic guiding field
of about 400 nT using LT$_C$ SQUIDs as low-noise magnetic flux detectors. The
transverse relaxation rates of both spin species are simultaneously monitored
as magnetic field gradients are varied. For transverse relaxation times
reaching 100 h, the residual longitudinal field gradient across the spin sample
could be deduced to be$|\vec{\nabla}B_z|=(5.6 \pm 0.4)$ pT/cm. The method takes
advantage of the high signal-to-noise ratio with which the decaying spin
precession signal can be monitored that finally leads to the exceptional
accuracy to determine magnetic field gradients at the sub pT/cm scale.

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The categories of this paper are: funct-an
0
The categories of this paper are: hep-ph
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The categories of this paper are: ao-sci
14
The categories of this paper are: math-ph
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The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph
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The categories of this paper are: acc-phys
7
The categories of this paper are: hep-th
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The categories of this paper are: chem-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: plasm-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: eess
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The categories of this paper are: adap-org
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The categories of this paper are: hep-ex
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The categories of this paper are: cs