138 research outputs found
NMR detection with an atomic magnetometer
We demonstrate detection of NMR signals using a non-cryogenic atomic
magnetometer and describe several novel applications of this technique. A water
free induction decay (FID) signal in a 0.5 T field is detected using a
spin-exchange-relaxation-free K magnetometer and the possibility of using a
multi-channel magnetometer for 3-D MRI requiring only a single FID signal is
described. We also demonstrate detection of less than Xe
atoms whose NMR signal is enhanced by a factor of 540 due to Fermi-contact
interaction with K atoms. This technique allows detection of less than
Xe spins in a flowing system suitable for remote NMR applications
High-Temperature Alkali Vapor Cells with Anti-Relaxation Surface Coatings
Antirelaxation surface coatings allow long spin relaxation times in
alkali-metal cells without buffer gas, enabling faster diffusion of the alkali
atoms throughout the cell and giving larger signals due to narrower optical
linewidths. Effective coatings were previously unavailable for operation at
temperatures above 80 C. We demonstrate that octadecyltrichlorosilane (OTS) can
allow potassium or rubidium atoms to experience hundreds of collisions with the
cell surface before depolarizing, and that an OTS coating remains effective up
to about 170 C for both potassium and rubidium. We consider the experimental
concerns of operating without buffer gas and with minimal quenching gas at high
vapor density, studying the stricter need for effective quenching of excited
atoms and deriving the optical rotation signal shape for atoms with resolved
hyperfine structure in the spin-temperature regime. As an example of a
high-temperature application of antirelaxation coated alkali vapor cells, we
operate a spin-exchange relaxation-free atomic magnetometer with sensitivity of
6 fT/sqrt(Hz) and magnetic linewidth as narrow as 2 Hz.Comment: 8 pages, 5 figures. The following article appeared in Journal of
Applied Physics and may be found at http://link.aip.org/link/?jap/106/11490
Sub-femtotesla scalar atomic magnetometer using multipass cells
Scalar atomic magnetometers have many attractive features but their
sensitivity has been relatively poor. We describe a Rb scalar gradiometer using
two multi-pass optical cells. We use a pump-probe measurement scheme to
suppress spin-exchange relaxation and two probe pulses to find the spin
precession zero crossing times with a resolution of 1 psec. We realize magnetic
field sensitivity of 0.54 fT/Hz, which improves by an order of
magnitude the best scalar magnetometer sensitivity and surpasses the quantum
limit set by spin-exchange collisions for a scalar magnetometer with the same
measurement volume operating in a continuous regime.Comment: 5 pages, 4 figure
Correlation function of spin noise due to atomic diffusion
We use paramagnetic Faraday rotation to study spin noise spectrum from
unpolarized Rb vapor in a tightly focused probe beam in the presence of N
buffer gas. We derive an analytical form for the diffusion component of the
spin noise time-correlation function in a Gaussian probe beam. We also obtain
analytical forms for the frequency spectrum of the spin noise in the limit of a
tightly focused or a collimated Gaussian beam in the presence of diffusion. In
particular, we find that in a tightly focused probe beam the spectral lineshape
can be independent of the buffer gas pressure. Experimentally, we find good
agreement between the calculated and measured spin noise spectra for N gas
pressures ranging from 56 to 820 torr.Comment: 6 pages, 4 figure
Non-linear amplification of small spin precession using long range dipolar interactions
In measurements of small signals using spin precession the precession angle
usually grows linearly in time. We show that non-linear interactions between
particles can lead to an exponentially growing spin precession angle, resulting
in an amplification of small signals and raising them above the noise level of
a detection system. We demonstrate amplification by a factor of greater than 8
of a spin precession signal due to a small magnetic field gradient in a
spherical cell filled with hyperpolarized liquid Xe. This technique can
improve the sensitivity in many measurements that are limited by the noise of
the detection system, rather then the fundamental spin-projection noise.Comment: 4 pages, 4 figure
Stroboscopic back-action evasion in a dense alkali-metal vapor
We explore experimentally quantum non-demolition (QND) measurements of atomic
spin in a hot potassium vapor in the presence of spin-exchange relaxation. We
demonstrate a new technique for back-action evasion by stroboscopic modulation
of the probe light. With this technique we study spin noise as a function of
polarization for atoms with spin greater than 1/2 and obtain good agreement
with a simple theoretical model. We point that in a system with fast
spin-exchange, where the spin relaxation rate is changing with time, it is
possible to improve the long-term sensitivity of atomic magnetometry by using
QND measurements
Limits on new long range nuclear spin-dependent forces set with a K-3He co-magnetometer
A magnetometer using spin-polarized K and He atoms occupying the same
volume is used to search for anomalous nuclear spin-dependent forces generated
by a separate He spin source. We measure changes in the He spin
precession frequency with a resolution of 18 pHz and constrain anomalous spin
forces between neutrons to be less than of their magnetic or
less than of their gravitational interactions on a length
scale of 50 cm. We present new limits on neutron coupling to light pseudoscalar
and vector particles, including torsion, and constraints on recently proposed
models involving unparticles and spontaneous breaking of Lorentz symmetry.Comment: 4 pages, 4 figures, latest version as appeared in PR
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