555 research outputs found
A Precessing Ferromagnetic Needle Magnetometer
A ferromagnetic needle is predicted to precess about the magnetic field axis
at a Larmor frequency under conditions where its intrinsic spin
dominates over its rotational angular momentum, ( is
the moment of inertia of the needle about the precession axis and is the
number of polarized spins in the needle). In this regime the needle behaves as
a gyroscope with spin maintained along the easy axis of the needle by
the crystalline and shape anisotropy. A precessing ferromagnetic needle is a
correlated system of spins which can be used to measure magnetic fields for
long times. In principle, by taking advantage of rapid averaging of quantum
uncertainty, the sensitivity of a precessing needle magnetometer can far
surpass that of magnetometers based on spin precession of atoms in the gas
phase. Under conditions where noise from coupling to the environment is
subdominant, the scaling with measurement time of the quantum- and
detection-limited magnetometric sensitivity is . The phenomenon of
ferromagnetic needle precession may be of particular interest for precision
measurements testing fundamental physics.Comment: Main text: 6 pages, 2 figures; Supplementary material: 3 pages, 1
figur
Magnetic shielding and exotic spin-dependent interactions
Experiments searching for exotic spin-dependent interactions typically employ
magnetic shielding between the source of the exotic field and the interrogated
spins. We explore the question of what effect magnetic shielding has on
detectable signals induced by exotic fields. Our general conclusion is that for
common experimental geometries and conditions, magnetic shields should not
significantly reduce sensitivity to exotic spin-dependent interactions,
especially when the technique of comagnetometry is used. However, exotic fields
that couple to electron spin can induce magnetic fields in the interior of
shields made of a soft ferro- or ferrimagnetic material. This induced magnetic
field must be taken into account in the interpretation of experiments searching
for new spin-dependent interactions and raises the possibility of using a flux
concentrator inside magnetic shields to amplify exotic spin-dependent signals.Comment: 8 pages, 5 figure
How do you know if you ran through a wall?
Stable topological defects of light (pseudo)scalar fields can contribute to
the Universe's dark energy and dark matter. Currently the combination of
gravitational and cosmological constraints provides the best limits on such a
possibility. We take an example of domain walls generated by an axion-like
field with a coupling to the spins of standard-model particles, and show that
if the galactic environment contains a network of such walls, terrestrial
experiments aimed at detection of wall-crossing events are realistic. In
particular, a geographically separated but time-synchronized network of
sensitive atomic magnetometers can detect a wall crossing and probe a range of
model parameters currently unconstrained by astrophysical observations and
gravitational experiments.Comment: 5 pages, 2 figure; to appear in the PR
Influence of magnetic-field inhomogeneity on nonlinear magneto-optical resonances
In this work, a sensitivity of the rate of relaxation of ground-state atomic
coherences to magnetic-field inhomogeneities is studied. Such coherences give
rise to many interesting phenomena in light-atom interactions, and their
lifetimes are a limiting factor for achieving better sensitivity, resolution or
contrast in many applications. For atoms contained in a vapor cell, some of the
coherence-relaxation mechanisms are related to magnetic-field inhomogeneities.
We present a simple model describing relaxation due to such inhomogeneities in
a buffer-gas-free anti-relaxation coated cell. A relation is given between
relaxation rate and magnetic-field inhomogeneities including the dependence on
cell size and atomic spices. Experimental results, which confirm predictions of
the model, are presented. Different regimes, in which the relaxation rate is
equally sensitive to the gradients in any direction and in which it is
insensitive to gradients transverse to the bias magnetic field, are predicted
and demonstrated experimentally.Comment: 6 pages, 4 figures, Submitted to Phys. Rev.
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