16,198 research outputs found
Quantum correlated light pulses from sequential superradiance of a condensate
We discover an inherent mechanism for entanglement swap associated with
sequential superradiance from an atomic Bose-Einstein condensate. Based on
careful examinations with both analytical and numerical approaches, we conclude
that as a result of the swap mechanism, Einstein-Podolsky-Rosen (EPR)-type
quantum correlations can be detected among the scattered light pulses.Comment: 10 pages, 6 figure
Tunnelling of condensate magnetization in a double-well potential
We study quantum dynamical properties of a spin-1 atomic Bose-Einstein
condensate in a double-well potential. Adopting a mean field theory and single
spatial mode approximation, we characterize our model system as two coupled
spins. For certain initial states, we find full magnetization oscillations
between wells not accompanied by mass (or atom numbers) exchange. We identify
dynamic regimes of collective spin variables arising from nonlinear
self-interactions that are different from the usual Josephson oscillations. We
also discuss magnetization beats and incomplete oscillations of collective spin
variables other than the magnetization. Our study points to an alternative
approach to observe coherent tunnelling of a condensate through a (spatial)
potential barrier.Comment: 5 pages, 5 figures, submitted to Physical Review
Superradiance induced topological vortex phase in a Bose-Einstein condensate
We investigate theoretically a topological vortex phase transition induced by
a superradiant phase transition in an atomic Bose-Einstein condensate driven by
a Laguerre-Gaussian optical mode. We show that superradiant radiation can
either carry zero angular momentum, or be in a rotating Laguerre-Gaussian mode
with angular momentum. The conditions leading to these two regimes are
determined in terms of the width for the pump laser and the condensate size for
the limiting cases where the recoil energy is both much smaller and larger than
the atomic interaction energy.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Spin dynamics of two-dimensional electrons with Rashba spin-orbit coupling and electron-electron interactions
We study the spin dynamics of two dimensional electron gases (2DEGs) with
Rashba spin-orbit coupling by taking account of electron-electron interactions.
The diffusion equations for charge and spin densities are derived by making use
of the path-integral approach and the quasiclassical Green's function.
Analyzing the effect of the interactions, we show that the spin-relaxation time
can be enhanced by the electron-electron interaction in the ballistic regime.Comment: accepted for publication in Phys. Rev.
Measuring the quality factor of a microwave cavity using superconduting qubit devices
We propose a method to create superpositions of two macroscopic quantum
states of a single-mode microwave cavity field interacting with a
superconducting charge qubit. The decoherence of such superpositions can be
determined by measuring either the Wigner function of the cavity field or the
charge qubit states. Then the quality factor Q of the cavity can be inferred
from the decoherence of the superposed states. The proposed method is
experimentally realizable within current technology even when the value is
relatively low, and the interaction between the qubit and the cavity field is
weak.Comment: 8 page
Basic Representations of A_{2l}^(2) and D_{l+1}^(2) and the Polynomial Solutions to the Reduced BKP Hierarchies
Basic representations of A_{2l}^(2) and D_{l+1}^(2) are studied. The weight
vectors are represented in terms of Schur's -functions. The method to get
the polynomial solutions to the reduced BKP hierarchies is shown to be
equivalent to a certain rule in Maya game.Comment: January 1994, 11 page
Genghis Khan's death (AD 1227): An unsolvable riddle or simply a pandemic disease?
The article examines Genghis Khan's death from the historico-medical perspective. Although several etiologies have been proposed over the years, most of these at a closer look appear to be later inventions by historians. A reassessment of the available evidence suggests instead bubonic plague as the most likely clinical scenario. Genghis Khan's death is also a reflection on the impact of pandemic diseases on leadership in ancient times as well as nowadays
Clusters in the Luminous Giant HII Regions in M101
(Abridged) We have obtained HST WFPC2 observations of three very luminous but
morphologically different giant HII regions (GHRs) in M101, NGC5461, NGC5462,
and NGC5471, in order to study cluster formation in GHRs. The measured (M_F547M
- M_F675W) colors and M_F547M magnitudes are used to determine the ages and
masses of the cluster candidates with M_F547M <= -9.0. NGC5461 is dominated by
a very luminous core, and has been suggested to host a super-star cluster
(SSC). Our observations show that it contains three R136-class clusters
superposed on a bright stellar background in a small region. This tight group
of clusters may dynamically evolve into an SSC in the future, and may appear
unresolved and be identified as an SSC at large distances, but at present
NGC5461 has no SSCs. NGC5462 has loosely distributed HII regions and clusters
without a prominent core. It has the largest number of cluster candidates among
the three GHRs, but most of them are faint and older than 10 Myr. NGC5471 has
multiple bright HII regions, and contains a large number of faint clusters
younger than 5 Myr. Two of the clusters in NGC5471 are older than R136, but
just as luminous; they may be the most massive clusters in the three GHRs. The
fraction of stars formed in massive clusters is estimated from the clusters'
contribution to the total stellar continuum emission and a comparison of the
ionizing power of the clusters to the ionizing requirement of the associated
HII regions. Both estimates show that <~ 50% of massive stars are formed in
massive clusters. The cluster luminosity functions (CLFs) of the three GHRs
show different slopes. NGC5462 has the steepest CLF and the most loosely
distributed interstellar gas, qualitatively consistent with the hypothesis that
massive clusters are formed in high-pressure interstellar environments.Comment: 36 pages (figures not included), 16 figures (3 of them are color
figures). Figures are in JPEG or GIF format with a lower resolution due to
the size limit of the file. For a higher resolution version of the paper,
please download from http://www.astro.uiuc.edu/~c-chen/clusters.pdf. accepted
for ApJ (scheduled for the ApJ 2005 February issue
Quantum entanglement of spin-1 bosons with coupled ground states in optical lattices
We examine particle entanglement, characterized by pseudo-spin squeezing, of
spin-1 bosonic atoms with coupled ground states in a one-dimensional optical
lattice. Both the superfluid and Mott-insulator phases are investigated
separately for ferromagnetic and antiferromagnetic interactions. Mode
entanglement is also discussed in the Mott insulating phase. The role of a
small but nonzero angle between the polarization vectors of counter-propagating
lasers forming the optical lattice on quantum correlations is investigated as
well.Comment: 18 pages, 8 figures. To be published in Journal of Physics
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