186 research outputs found
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
A low-noise ferrite magnetic shield
Ferrite materials provide magnetic shielding performance similar to commonly
used high permeability metals but have lower intrinsic magnetic noise generated
by thermal Johnson currents due to their high electrical resistivity.
Measurements inside a ferrite shield with a spin-exchange relaxation-free
atomic magnetometer reveal a noise level of 0.75 fT Hz^(-1/2), 25 times lower
than what would be expected in a comparable mu-metal shield. The authors
identify a 1/f component of the magnetic noise due to magnetization
fluctuations and derive general relationships for the Johnson current noise and
magnetization noise in cylindrical ferromagnetic shields in terms of their
conductivity and complex magnetic permeability.Comment: 4 pages, 3 figures. Published in Appl. Phys. Lett.; replacement
reflects published wor
High Bandwidth Atomic Magnetometery with Continuous Quantum Non-demolition Measurements
We describe an experimental study of spin-projection noise in a high
sensitivity alkali-metal magnetometer. We demonstrate a four-fold improvement
in the measurement bandwidth of the magnetometer using continuous quantum
non-demolition (QND) measurements. Operating in the scalar mode with a
measurement volume of 2 cm^3 we achieve magnetic field sensitivity of 22
fT/Hz^(1/2) and a bandwidth of 1.9 kHz with a spin polarization of only 1%. Our
experimental arrangement is naturally back-action evading and can be used to
realize sub-fT sensitivity with a highly polarized spin-squeezed atomic vapor.Comment: 4 page
A Low-Noise High-Density Alkali Metal Scalar Magnetometer
We present an experimental and theoretical study of a scalar atomic
magnetometer using an oscillating field-driven Zeeman resonance in a
high-density optically-pumped potassium vapor. We describe an experimental
implementation of an atomic gradiometer with a noise level below 10
fT/Hz^{1/2}, fractional field sensitivity below 10^{-9}/Hz^{1/2}, and an active
measurement volume of about 1.5 cm^3. We show that the fundamental field
sensitivity of a scalar magnetometer is determined by the rate of alkali-metal
spin-exchange collisions even though the resonance linewidth can be made much
smaller than the spin-exchange rate by pumping most atoms into a stretched spin
state.Comment: 10 pages, 7 figures. Version 2 is longer, with more complete
description of theoretical analysis and comparison between analytical and
experimental result
CP violation versus flavour in supersymmetric theories
We show that the quark flavour structure and CP violating phenomena are
strongly correlated in supersymmetric theories. For a generic pattern of
supersymmetry breaking the two broad categories of Yukawa couplings, democratic
and hierarchical textures, have entirely different phenomenological
implications. With hierarchical Yukawas, the rephasing invariant phase,
arg(V_us V_cb V_cb^* V_cs^*), in the CKM mixing matrix has to be of order
unity, while the SUSY CP violating phases are severely constrained by electric
dipole moments, giving rise to the so-called SUSY CP problem. With democratic
Yukawas, all experimental CP results can be accommodated with small values for
the CKM and SUSY CP violating phases (i.e., CP can be considered as an
approximate symmetry at the high energy scale). We also show that within this
scenario, an entirely real CKM matrix in supersymmetric models is still allowed
by the present experimental results.Comment: 16 pages, 6 eps figure
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