4,669 research outputs found
Comments on "Limits on possible new nucleon monopole-dipole interactions from the spin relaxation rate of polarized He gas"
In the article "Limits on possible new nucleon monopole-dipole interactions
from the spin relaxation rate of polarized He gas", new limits on
short-range, Axion-like interactions are presented. In this comment it is shown
that the theoretical treatement of the data overestimates the sensitivity of
the proposed method. We provide the corrected limits
Geometric phases in electric dipole searches with trapped spin-1/2 particles in general fields and measurement cells of arbitrary shape with smooth or rough walls
The important role of geometric phases in searches for a permanent electric
dipole moment of the neutron, using Ramsey separated oscillatory field nuclear
magnetic resonance, was first noted by Commins and investigated in detail by
Pendlebury et al. Their analysis was based on the Bloch equations. In
subsequent work using the spin density matrix Lamoreaux and Golub showed the
relation between the frequency shifts and the correlation functions of the
fields seen by trapped particles in general fields (Redfield theory). More
recently we presented a solution of the Schr\"odinger equation for spin-
particles in circular cylindrical traps with smooth walls and exposed to
arbitrary fields [Steyerl et al.] Here we extend this work to show how the
Redfield theory follows directly from the Schr\"odinger equation solution. This
serves to highlight the conditions of validity of the Redfield theory, a
subject of considerable discussion in the literature [e.g., Nicholas et al.]
Our results can be applied where the Redfield result no longer holds, such as
observation times on the order of or shorter than the correlation time and
non-stochastic systems and thus we can illustrate the transient spin dynamics,
i.e. the gradual development of the shift with increasing time subsequent to
the start of the free precession. We consider systems with rough, diffuse
reflecting walls, cylindrical trap geometry with arbitrary cross section, and
field perturbations that do not, in the frame of the moving particles, average
to zero in time. We show by direct, detailed, calculation the agreement of the
results from the Schr\"odinger equation with the Redfield theory for the cases
of a rectangular cell with specular walls and of a circular cell with diffuse
reflecting walls.Comment: 20 pages, 8 figure
Frequency shifts and relaxation rates for spin 1/2 particles moving in electromagnetic fields
We discuss the behaviour of the Larmor frequency shift and the longitudinal
relaxation rate due to non-uniform electromagnetic fields on an assembly of
spin 1/2 particles, in adiabatic and nonadiabatic regimes. We also show some
general relations between the various frequency shifts and between the
frequency shifts and relaxation rates. The remarkable feature of all our
results is that they were obtained without any specific assumptions on the
explicit form of the correlation functions of the fields. Hence, we expect that
our results are valid both for diffusive and ballistic regime of motion and
arbitrary cell shapes and surface scattering. These results can then be applied
to a wide variety of realistic systems
The Child is Father of the Man: Foresee the Success at the Early Stage
Understanding the dynamic mechanisms that drive the high-impact scientific
work (e.g., research papers, patents) is a long-debated research topic and has
many important implications, ranging from personal career development and
recruitment search, to the jurisdiction of research resources. Recent advances
in characterizing and modeling scientific success have made it possible to
forecast the long-term impact of scientific work, where data mining techniques,
supervised learning in particular, play an essential role. Despite much
progress, several key algorithmic challenges in relation to predicting
long-term scientific impact have largely remained open. In this paper, we
propose a joint predictive model to forecast the long-term scientific impact at
the early stage, which simultaneously addresses a number of these open
challenges, including the scholarly feature design, the non-linearity, the
domain-heterogeneity and dynamics. In particular, we formulate it as a
regularized optimization problem and propose effective and scalable algorithms
to solve it. We perform extensive empirical evaluations on large, real
scholarly data sets to validate the effectiveness and the efficiency of our
method.Comment: Correct some typos in our KDD pape
Geometry of effective Hamiltonians
We give a complete geometrical description of the effective Hamiltonians
common in nuclear shell model calculations. By recasting the theory in a
manifestly geometric form, we reinterpret and clarify several points. Some of
these results are hitherto unknown or unpublished. In particular, commuting
observables and symmetries are discussed in detail. Simple and explicit proofs
are given, and numerical algorithms are proposed, that improve and stabilize
common methods used today.Comment: 1 figur
Spin and transport effects in quantum microcavities with polarization splitting
Transport properties of exciton-polaritons in anisotropic quantum
microcavities are considered theoretically. Microscopic symmetry of the
structure is taken into account by allowing for both the
longitudinal-transverse (TE-TM) and anisotropic splitting of polariton states.
The splitting is equivalent to an effective magnetic field acting on polariton
pseudospin, and polarization conversion in microcavities is shown to be caused
by an interplay of exciton-polariton spin precession and elastic scattering. In
addition, we considered the spin-dependent interference of polaritons leading
to weak localization and calculated coherent backscattering intensities in
different polarizations. Our findings are in a very good agreement with the
recent experimental data.Comment: 8 pages, 6 figure
Deformed Wigner crystal in a one-dimensional quantum dot
The spatial Fourier spectrum of the electron density distribution in a finite
1D system and the distribution function of electrons over single-particle
states are studied in detail to show that there are two universal features in
their behavior, which characterize the electron ordering and the deformation of
Wigner crystal by boundaries. The distribution function has a -like
singularity at the Fermi momentum . The Fourier spectrum of the density
has a step-like form at the wavevector , with the harmonics being absent
or vanishing above this threshold. These features are found by calculations
using exact diagonalization method. They are shown to be caused by Wigner
ordering of electrons, affected by the boundaries. However the common Luttinger
liquid model with open boundaries fails to capture these features, because it
overestimates the deformation of the Wigner crystal. An improvement of the
Luttinger liquid model is proposed which allows one to describe the above
features correctly. It is based on the corrected form of the density operator
conserving the particle number.Comment: 10 pages, 11 figures. Misprints fixe
Calculation of geometric phases in electric dipole searches with trapped spin-1/2 particles based on direct solution of the Schr\"odinger equation
Pendlebury [Phys. Rev. A , 032102 (2004)] were
the first to investigate the role of geometric phases in searches for an
electric dipole moment (EDM) of elementary particles based on Ramsey-separated
oscillatory field magnetic resonance with trapped ultracold neutrons and
comagnetometer atoms. Their work was based on the Bloch equation and later work
using the density matrix corroborated the results and extended the scope to
describe the dynamics of spins in general fields and in bounded geometries. We
solve the Schr\"odinger equation directly for cylindrical trap geometry and
obtain a full description of EDM-relevant spin behavior in general fields,
including the short-time transients and vertical spin oscillation in the entire
range of particle velocities. We apply this method to general macroscopic
fields and to the field of a microscopic magnetic dipole.Comment: 11 pages, 4 figure
Optimal purification of a generic n-qudit state
We propose a quantum algorithm for the purification of a generic mixed state
of a -qudit system by using an ancillary -qudit system. The
algorithm is optimal in that (i) the number of ancillary qudits cannot be
reduced, (ii) the number of parameters which determine the purification state
exactly equals the number of degrees of freedom of , and (iii)
is easily determined from the density matrix . Moreover, we
introduce a quantum circuit in which the quantum gates are unitary
transformations acting on a -qudit system. These transformations are
determined by parameters that can be tuned to generate, once the ancillary
qudits are disregarded, any given mixed -qudit state.Comment: 8 pages, 9 figures, remarks adde
Fluctuation-induced interactions between dielectrics in general geometries
We study thermal Casimir and quantum non-retarded Lifshitz interactions
between dielectrics in general geometries. We map the calculation of the
classical partition function onto a determinant which we discretize and
evaluate with the help of Cholesky factorization. The quantum partition
function is treated by path integral quantization of a set of interacting
dipoles and reduces to a product of determinants. We compare the approximations
of pairwise additivity and proximity force with our numerical methods. We
propose a ``factorization approximation'' which gives rather good numerical
results in the geometries that we study
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