939 research outputs found
On the Correlation Between Polarized BECs
We consider the channels synthesized by the -fold application of
Ar\i{}kan's polar transform to a binary erasure channel (BEC). The synthetic
channels are BECs themselves, and we show that, asymptotically for almost all
these channels, the pairwise correlations between their erasure events are
extremely small: the correlation coefficients vanish faster than any
exponential in . Such a fast decay of correlations allows us to conclude
that the union bound on the block error probability of polar codes is very
tight.Comment: 9 pages, Extended version of a paper submitted to ISIT 201
Split spin-squeezed Bose-Einstein Condensates
We investigate and model the behaviour of split spin-squeezed Bose-Einstein
condensates (BECs) system. In such a system, a spin-polarized BEC is first
squeezed using a interaction, then are split into two separate
clouds. After the split, we consider that the particle number in each cloud
collapses to a fixed number. We show that this procedure is equivalent to
applying an interaction corresponding to squeezing each cloud individually plus
an entangling operation. We analyse the system's entanglement properties and
show that it can be detected using correlation-based entanglement criteria. The
nature of the states are illustrated by Wigner functions and have the form of a
correlated squeezed state. The conditional Wigner function shows high degrees
of non-classicality for dimensionless squeezing times beyond ,
where is the number of particles per BEC.Comment: 11 pages, 7 figure
Correlation-based entanglement criterion in bipartite multiboson systems
We describe a criterion for the detection of entanglement between two
multi-boson systems. The criterion is based on calculating correlations of
Gell-Mann matrices with a fixed boson number on each subsystem. This applies
naturally to systems such as two entangled spinor Bose-Einstein condensates. We
apply our criterion to several experimentally motivated examples, such as an entangled BECs, ac Stark shift induced two-mode squeezed BECs, and
photons under parametric down conversion. We find that entanglement can be
detected for all parameter regions for the most general criterion. Alternative
criteria based on a similar formalism are also discussed together with their
merits.Comment: 8 pages, 4 figures, journal versio
Experimental study of the transport of coherent interacting matter-waves in a 1D random potential induced by laser speckle
We present a detailed analysis of the 1D expansion of a coherent interacting
matterwave (a Bose-Einstein condensate) in the presence of disorder. A 1D
random potential is created via laser speckle patterns. It is carefully
calibrated and the self-averaging properties of our experimental system are
discussed. We observe the suppression of the transport of the BEC in the random
potential. We discuss the scenario of disorder-induced trapping taking into
account the radial extension in our experimental 3D BEC and we compare our
experimental results with the theoretical predictions
Spinor Bose-Einstein condensates
An overview on the physics of spinor and dipolar Bose-Einstein condensates
(BECs) is given. Mean-field ground states, Bogoliubov spectra, and many-body
ground and excited states of spinor BECs are discussed. Properties of
spin-polarized dipolar BECs and those of spinor-dipolar BECs are reviewed. Some
of the unique features of the vortices in spinor BECs such as fractional
vortices and non-Abelian vortices are delineated. The symmetry of the order
parameter is classified using group theory, and various topological excitations
are investigated based on homotopy theory. Some of the more recent developments
in a spinor BEC are discussed.Comment: To appear in Physics Reports. The PDF file with high resolution
figures is available from the following website:
http://cat.phys.s.u-tokyo.ac.jp/publication/review_of_spinorBEC.pd
Bose-Einstein correlations in hadron-pairs from lepto-production on nuclei ranging from hydrogen to xenon
Bose-Einstein correlations of like-sign charged hadrons produced in
deep-inelastic electron and positron scattering are studied in the HERMES
experiment using nuclear targets of H, H, He, He, N, Ne, Kr,
and Xe. A Gaussian approach is used to parametrize a two-particle correlation
function determined from events with at least two charged hadrons of the same
sign charge. This correlation function is compared to two different empirical
distributions that do not include the Bose-Einstein correlations. One
distribution is derived from unlike-sign hadron pairs, and the second is
derived from mixing like-sign pairs from different events. The extraction
procedure used simulations incorporating the experimental setup in order to
correct the results for spectrometer acceptance effects, and was tested using
the distribution of unlike-sign hadron pairs. Clear signals of Bose-Einstein
correlations for all target nuclei without a significant variation with the
nuclear target mass are found. Also, no evidence for a dependence on the
invariant mass W of the photon-nucleon system is found when the results are
compared to those of previous experiments
Holographic storage of multiple coherence gratings in a Bose-Einstein condensate
We demonstrate superradiant conversion between a two-mode collective atomic
state and a single-mode light field in an elongated cloud of Bose-condensed
atoms. Two off-resonant write beams induce superradiant Raman scattering,
producing two independent coherence gratings with a different wave vector in
the cloud. By applying phase-matched read beams after a controllable delay, the
gratings can be selectively converted into the light field also in a
superradiant way. Due to the large cooperativity parameter and the small
velocity width of the condensate, a high conversion efficiency of % and
a long storage time of s were achieved.Comment: 5 pages, 4 figure
Magnetoelectric Properties of Pb Free Bi2FeTiO6: A Theoretical Investigation
The structural, electronic, magnetic and ferroelectric properties of Pb free
double perovskite multiferroic Bi2FeTiO6 are investigated using density
functional theory within the general gradient approximation (GGA) method. Our
structural optimization using total energy calculations for different potential
structures show a minimum energy for a non-centrosymmetric rhombohedral
structure with R3 space group. Bi2FeTiO6 is found to be an antiferromagnetic
insulator with C-type magnetic ordering with bandgap value of 0.3 eV. The
calculated magnetic moment of 3.52 \mu_B at Fe site shows the high spin
arrangement of 3d electrons which is also confirmed by our orbital projected
density of states analysis. We have analyzed the characteristics of bonding
present between the constituents of Bi2FeTiO6 with the help of calculated
partial density of states and Born effective charges. The ground state of the
nearest centrosymmetric structure is found to be a G-type antiferromagnet with
half metallicity showing that by the application of external electric field we
can not only get a polarized state but also change the magnetic ordering and
electronic structure in the present compound indicating strong magnetoelectric
coupling. The cation sites the coexistence of Bi 6s lone pair (bring
disproportionate charge distribution) and Ti4+ d0 ions which brings covalency
produces off-center displacement and favors a non-centrosymmetric ground state
and thus ferroelectricity. Our Berry phase calculation gives a polarization of
48 \muCcm-2 for Bi2FeTiO6.Comment: 4 pages, 5 picture
Quantized vortices in superfluid helium and atomic Bose-Einstein condensates
This article reviews recent developments in the physics of quantized vortices
in superfluid helium and atomic Bose-Einstein condensates. Quantized vortices
appear in low-temperature quantum condensed systems as the direct product of
Bose-Einstein condensation. Quantized vortices were first discovered in
superfluid 4He in the 1950s, and have since been studied with a primary focus
on the quantum hydrodynamics of this system. Since the discovery of superfluid
3He in 1972, quantized vortices characteristic of the anisotropic superfluid
have been studied theoretically and observed experimentally using rotating
cryostats. The realization of atomic Bose-Einstein condensation in 1995 has
opened new possibilities, because it became possible to control and directly
visualize condensates and quantized vortices. Historically, many ideas
developed in superfluid 4He and 3He have been imported to the field of cold
atoms and utilized effectively. Here, we review and summarize our current
understanding of quantized vortices, bridging superfluid helium and atomic
Bose-Einstein condensates. This review article begins with a basic
introduction, which is followed by discussion of modern topics such as quantum
turbulence and vortices in unusual cold atom condensates.Comment: 99 pages, 20 figures, Review articl
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