826 research outputs found
Constraints on short-range spin-dependent interactions from scalar spin-spin coupling in deuterated molecular hydrogen
A comparison between existing measurements and calculations of the scalar
spin-spin interaction (J-coupling) in deuterated molecular hydrogen (HD) yields
stringent constraints on anomalous spin-dependent potentials between nucleons
at the atomic scale (). The dimensionless coupling constant
associated with exchange of pseudoscalar (axion-like)
bosons between nucleons is constrained to be less than for
boson masses in the range of . This represents improvement by a
factor of about 100 over constraints placed by measurements of the
dipole-dipole interaction in molecular . The dimensionless coupling
constant associated with exchange of a heretofore
undiscovered axial-vector boson between nucleons is constrained to be
for bosons of mass , improving constraints at this distance scale by a factor of 100 for
proton-proton couplings and more than 8 orders of magnitude for neutron-proton
couplings. This limit is also a factor of 100 more stringent than recent
constraints obtained for axial-vector couplings between electrons and nucleons
obtained from comparison of measurements and calculations of hyperfine
structure.Comment: 4 pages 2 figure
Spin Diffusion and Relaxation in a Nonuniform Magnetic Field
We consider a quasiclassical model that allows us to simulate the process of
spin diffusion and relaxation in the presence of a highly nonuniform magnetic
field. The energy of the slow relaxing spins flows to the fast relaxing spins
due to the dipole-dipole interaction between the spins. The magnetic field
gradient suppresses spin diffusion and increases the overall relaxation time in
the system. The results of our numerical simulations are in a good agreement
with the available experimental data.Comment: 11 pages and 6 figure
Reduction of Magnetic Noise in Magnetic Resonance Force Microscopy
We study the opportunity to reduce a magnetic noise produced by a uniform
cantilever with a ferromagnetic particle in magnetic resonance force microscopy
(MRFM) applications. We demonstrate theoretically a significant reduction of
magnetic noise and the corresponding increase of the MRFM relaxation time using
a nonuniform cantilever
Regular and Random Magnetic Resonance Force Microscopy Signal with a Cantilever Oscillating Parallel to a Sample Surface
We study theoretically the magnetic resonance force microscopy (MRFM) in
oscillating cantilever-driven adiabatic reversals (OSCAR) technique, for the
case when the cantilever tip oscillates parallel to the surface of a sample.
The main contribution to the MRFM signal is associated with a part of the
resonance slice near the surface of the sample. The regular (approximately
exponential) decay of the MRFM signal is followed by the non-dissipating random
signal. The Fourier spectrum of the random signal has a characteristic peak
which can be used for the identification of the signal.Comment: 9 pages, 5 figure
Formation of ions by high energy photons
We calculate the electron energy spectrum of ionization by a high energy
photon, accompanied by creation of electron-positron pair. The total cross
section of the process is also obtained. The asymptotics of the cross section
does not depend on the photon energies. At the photon energies exceeding a
certain value this appeares to to be the dominant mechanism of
formation of the ions. The dependence of on the value of nuclear
charge is obtained. Our results are consistent with experimental data.Comment: 16 pages, 6 figure
Photon storage in Lambda-type optically dense atomic media. II. Free-space model
In a recent paper [Gorshkov et al., Phys. Rev. Lett. 98, 123601 (2007)], we
presented a universal physical picture for describing a wide range of
techniques for storage and retrieval of photon wave packets in Lambda-type
atomic media in free space, including the adiabatic reduction of the photon
group velocity, pulse-propagation control via off-resonant Raman techniques,
and photon-echo based techniques. This universal picture produced an optimal
control strategy for photon storage and retrieval applicable to all approaches
and yielded identical maximum efficiencies for all of them. In the present
paper, we present the full details of this analysis as well some of its
extensions, including the discussion of the effects of non-degeneracy of the
two lower levels of the Lambda system. The analysis in the present paper is
based on the intuition obtained from the study of photon storage in the cavity
model in the preceding paper [Gorshkov et al., Phys. Rev. A 76, 033804 (2007)].Comment: 26 pages, 8 figures. V2: significant changes in presentation, new
references, higher resolution of figure
Photon storage in Lambda-type optically dense atomic media. III. Effects of inhomogeneous broadening
In a recent paper [Gorshkov et al., Phys. Rev. Lett. 98, 123601 (2007)] and
in the two preceding papers [Gorshkov et al., Phys. Rev. A 76, 033804 (2007);
76, 033805 (2007)], we used a universal physical picture to optimize and
demonstrate equivalence between a wide range of techniques for storage and
retrieval of photon wave packets in homogeneously broadened Lambda-type atomic
media, including the adiabatic reduction of the photon group velocity,
pulse-propagation control via off-resonant Raman techniques, and
photon-echo-based techniques. In the present paper, we generalize this
treatment to include inhomogeneous broadening. In particular, we consider the
case of Doppler-broadened atoms and assume that there is a negligible
difference between the Doppler shifts of the two optical transitions. In this
situation, we show that, at high enough optical depth, all atoms contribute
coherently to the storage process as if the medium were homogeneously
broadened. We also discuss the effects of inhomogeneous broadening in solid
state samples. In this context, we discuss the advantages and limitations of
reversing the inhomogeneous broadening during the storage time, as well as
suggest a way for achieving high efficiencies with a nonreversible
inhomogeneous profile.Comment: 15 pages, 8 figures. V2: minor changes in presentation, new
references, higher resolution of figure
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