765 research outputs found
Particle-Hole Asymmetry and Brightening of Solitons in A Strongly Repulsive BEC
We study solitary wave propagation in the condensate of a system of hard-core
bosons with nearest-neighbor interactions. For this strongly repulsive system,
the evolution equation for the condensate order parameter of the system,
obtained using spin coherent state averages is different from the usual
Gross-Pitaevskii equation (GPE). The system is found to support two kinds of
solitons when there is a particle-hole imbalance: a dark soliton that dies out
as the velocity approaches the sound velocity, and a new type of soliton which
brightens and persists all the way up to the sound velocity, transforming into
a periodic wave train at supersonic speed. Analogous to the GPE soliton, the
energy-momentum dispersion for both solitons is characterized by Lieb II modes.Comment: Accepted for publication in PRL, Nov 12, 200
Dimer Decimation and Intricately Nested Localized-Ballistic Phases of Kicked Harper
Dimer decimation scheme is introduced in order to study the kicked quantum
systems exhibiting localization transition. The tight-binding representation of
the model is mapped to a vectorized dimer where an asymptotic dissociation of
the dimer is shown to correspond to the vanishing of the transmission
coefficient thru the system. The method unveils an intricate nesting of
extended and localized phases in two-dimensional parameter space. In addition
to computing transport characteristics with extremely high precision, the
renormalization tools also provide a new method to compute quasienergy
spectrum.Comment: There are five postscript figures. Only half of the figure (3) is
shown to reduce file size. However, missing part is the mirror image of the
part show
Ordering of localized moments in Kondo lattice models
We describe the transition from a ferromagnetic phase, to a disordered para-
magnetic phase, which occurs in one-dimensional Kondo lattice models with
partial conduction band filling. The transition is the quantum order-disorder
transition of the transverse-field Ising chain, and reflects double-exchange
ordered regions of localized spins being gradually destroyed as the coupling to
the conduction electrons is reduced. For incommensurate conduction band
filling, the low-energy properties of the localized spins near the transition
are dominated by anomalous ordered (disordered) regions of localized spins
which survive into the paramagnetic (ferromagnetic) phase. Many interesting
properties follow, including a diverging susceptibility for a finite range of
couplings into the paramagnetic phase. Our critical line equation, together
with numerically determined transition points, are used to determine the range
of the double-exchange interaction. Models we consider are the spin 1/2 Kondo
lattices with antiferromagnetic (Kondo) coupling, with ferromagnetic (Hund's
rule) coupling, and the Kondo lattice with repulsive interactions between the
conduction electrons.Comment: 18 pages, 6 embedded eps figures. To appear in Phys Rev
Hanbury Brown-Twiss Interferometry for Fractional and Integer Mott Phases
Hanbury-Brown-Twiss interferometry (HBTI) is used to study integer and
fractionally filled Mott Insulator (MI) phases in period-2 optical
superlattices. In contrast to the quasimomentum distribution, this second order
interferometry pattern exhibits high contrast fringes in the it insulating
phases. Our detailed study of HBTI suggests that this interference pattern
signals the various superfluid-insulator transitions and therefore can be used
as a practical method to determine the phase diagram of the system. We find
that in the presence of a confining potential the insulating phases become
robust as they exist for a finite range of atom numbers. Furthermore, we show
that in the trapped case the HBTI interferogram signals the formation of the MI
domains and probes the shell structure of the system.Comment: 13 pages, 15 figure
Phase transitions, entanglement and quantum noise interferometry in cold atoms
We show that entanglement monotones can characterize the pronounced
enhancement of entanglement at a quantum phase transition if they are sensitive
to long-range high order correlations. These monotones are found to develop a
sharp peak at the critical point and to exhibit universal scaling. We
demonstrate that similar features are shared by noise correlations and verify
that these experimentally accessible quantities indeed encode entanglement
information and probe separability.Comment: 4 pages 4 figure
Study of fetomaternal arterial doppler parameters in early onset pre-eclampsia and its correlation with perinatal outcomes
Background: Development of pre-eclampsia (PE) at less than 34 weeks of gestation is known as early onset PE (EOPE) and is commonly associated with more severe adverse maternal and fetal outcomes. The purpose of this study was to study Doppler parameters of uterine, umbilical and fetal middle cerebral arteries exclusively in women with EOPE and its correlation with perinatal outcomes. This study was a hospital-based observational prospective study.Methods: 60 patient of early onset PE with singleton live pregnancy were included in the study and followed up. The results of sonographic and Doppler examination were analysed and correlated with perinatal outcomes.Results: Adverse perinatal outcomes were seen in 66.66% cases of early onset PE. To predict adverse perinatal outcomes, umbilical artery (Umb A) RI, PI were found to be most sensitive, cerebroplacental ratio (CPR) was most specific indicator with highest positive predictive value (PPV). Absent end diastolic flow /reverse end diastolic flow (AEDF/REDF) were ominous signs.Conclusions: Early onset PE is recently considered a more severe disease with different etiopathogenesis. Doppler study is the primary imaging modality for fetomaternal surveillance for follow up and prediction of perinatal outcome, thus allowing planning of timely management in early onset PE patients, as these patients are at higher risk of adverse perinatal outcomes
Preliminary Development of a Nearly-Instantaneous Three- Dimensional Imaging Technique for High-Speed Flow Fields
Recent advances in high-repetition rate laser and camera technology present a new opportunity to develop three-dimensional diagnostics for high-speed flows. The design of a three-dimensional imaging system based on a pulse burst laser, a high-speed laser scanner and a high speed camera is described here. The pulse burst laser system is the 5 th of its kind in the world and can produce high energy pulses at up to 10 MHz repetition rates. A highspeed optical deflector, such as a rotating mirror or acousto-optic deflector, can be used to rapidly deflect a laser sheet through the flow field. A high-speed camera can then be used to collect images at different planes in the flow field, from which a three-dimensional image can be reconstructed. The state-of-the-art of these technologies are described. The high-speed characteristics of an acousto-optic deflector were tested using an Nd:YAG laser where it was found that a full sweep through at least 32 resolvable spots could be completed in 10 μsec. Future work will include testing of a galvanometric scanning mirror and assembly of a complete system
Orbital Configurations and Magnetic Properties of Double-Layered Antiferromagnet CsCuClBr
We report the single-crystal X-ray analysis and magnetic properties of a new
double-layered perovskite antiferromagnet, CsCuClBr. This
structure is composed of CuClBr double layers with elongated
CuClBr octahedra and is closely related to the SrTiO
structure. An as-grown crystal has a singlet ground state with a large
excitation gap of K, due to the strong
antiferromagnetic interaction between the two layers. CsCuClBr
undergoes a structural phase transition at K accompanied
by changes in the orbital configurations of Cu ions. Once a
CsCuClBr crystal is heated above , its magnetic
susceptibility obeys the Curie-Weiss law with decreasing temperature even below
and does not exhibit anomalies at . This implies that in
the heated crystal, the orbital state of the high-temperature phase remains
unchanged below , and thus, this orbital state is the metastable
state. The structural phase transition at is characterized as an
order-disorder transition of Cu orbitals.Comment: 6pages. 6figures, to appear in J. Phys. Soc. Jpn. Vol.76 No.
Noise Correlations of Hard-core Bosons: Quantum Coherence and Symmetry Breaking
Noise correlations, such as those observable in the time of flight images of
a released cloud, are calculated for hard-core bosonic (HCB) atoms. We find
that the standard mapping of HCB systems onto spin-1/2 XY models fails in
application to computation of noise correlations due to the contribution of
multiply occupied virtual states in HCB systems. Such states do not exist in
spin models. An interesting manifestation of such states is the breaking of
particle-hole symmetry in HCB. We use noise correlations to explore quantum
coherence of strongly correlated bosons in the fermionized regime with and
without external parabolic confinement. Our analysis points to distinctive new
experimental signatures of the Mott phase.Comment: 17 pages, 6 figures. This is a detailed revised version of
quant-ph/0507153. It has been submitted to Journal of Physics B: the special
edition for the Cortona BEC worksho
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