263 research outputs found
First-principles quantum dynamics for fermions: Application to molecular dissociation
We demonstrate that the quantum dynamics of a many-body Fermi-Bose system can
be simulated using a Gaussian phase-space representation method. In particular,
we consider the application of the mixed fermion-boson model to ultracold
quantum gases and simulate the dynamics of dissociation of a Bose-Einstein
condensate of bosonic dimers into pairs of fermionic atoms. We quantify
deviations of atom-atom pair correlations from Wick's factorization scheme, and
show that atom-molecule and molecule-molecule correlations grow with time, in
clear departures from pairing mean-field theories. As a first-principles
approach, the method provides benchmarking of approximate approaches and can be
used to validate dynamical probes for characterizing strongly correlated phases
of fermionic systems.Comment: Final published versio
Atom-atom correlations in colliding Bose-Einstein condensates
We analyze atom-atom correlations in the s-wave scattering halo of two colliding condensates. By developing a simple perturbative approach, we obtain explicit analytic results for the collinear (CL) and back-to-back (BB) correlations corresponding to realistic density profiles of the colliding condensates with interactions. The results in the short-time limit are in agreement with the first-principles simulations using the positive-P representation and provide analytic insights into the experimental observations of Perrin et al. [Phys. Rev. Lett. 99, 150405 (2007)]. For long collision durations, we predict that the BB correlation becomes broader than the CL correlatio
Uniform semiclassical trace formula for U(3) --> SO(3) symmetry breaking
We develop a uniform semiclassical trace formula for the density of states of
a three-dimensional isotropic harmonic oscillator (HO), perturbed by a term
. This term breaks the U(3) symmetry of the HO, resulting in a
spherical system with SO(3) symmetry. We first treat the anharmonic term in
semiclassical perturbation theory by integration of the action of the perturbed
periodic HO orbits over the manifold P which characterizes
their 4-fold degeneracy. Then we obtain an analytical uniform trace formula
which in the limit of strong perturbations (or high energy) asymptotically goes
over into the correct trace formula of the full anharmonic system with SO(3)
symmetry, and in the limit (or energy) restores the HO trace
formula with U(3) symmetry. We demonstrate that the gross-shell structure of
this anharmonically perturbed system is dominated by the two-fold degenerate
diameter and circular orbits, and {\it not} by the orbits with the largest
classical degeneracy, which are the three-fold degenerate tori with rational
ratios of radial and angular frequencies. The same
holds also for the limit of a purely quartic spherical potential .Comment: LaTeX (revtex4), 26pp., 5 figures, 1 table; final version to be
published in J. Phys. A (without appendices C and D
Bell's inequality for n spin-s particles
The Mermin-Klyshko inequality for n spin-1/2 particles and two dichotomic
observables is generalized to n spin-s particles and two maximal observables.
It is shown that some multiparty multilevel Greenberger-Horne-Zeilinger states
[A. Cabello, Phys. Rev. A 63, 022104 (2001)] maximally violate this inequality
for any s. For a fixed n, the magnitude of the violation is constant for any s,
which provides a simple demonstration and generalizes the conclusion reached by
Gisin and Peres for two spin-s particles in the singlet state [Phys. Lett. A
162, 15 (1992)]. For a fixed s, the violation grows exponentially with n, which
provides a generalization to any s of Mermin's conclusion for n spin-1/2
particles [Phys. Rev. Lett. 65, 1838 (1990)].Comment: REVTeX4, 4 page
Semiclassical description of shell effects in finite fermion systems
A short survey of the semiclassical periodic orbit theory, initiated by M.
Gutzwiller and generalized by many other authors, is given. Via so-called
semiclassical trace formmulae, gross-shell effects in bound fermion systems can
be interpreted in terms of a few periodic orbits of the corresponding classical
systems. In integrable systems, these are usually the shortest members of the
most degenerate families or orbits, but in some systems also less degenerate
orbits can determine the gross-shell structure. Applications to nuclei, metal
clusters, semiconductor nanostructures, and trapped dilute atom gases are
discussed.Comment: LaTeX (revteX4) 6 pages; invited talk at Int. Conference "Finite
Fermionic Systems: Nilsson Model 50 Years", Lund, Sweden, June 14-18, 200
Faraday waves in quasi-one-dimensional superfluid Fermi-Bose mixtures
Generation of Faraday waves in superfluid Fermi-Bose mixtures in elongated
traps is investigated. The generation of waves is achieved by periodically
changing a parameter of the system in time. Two types of modulations of
parameters are considered, first a variation of the fermion-bosons scattering
length, and secondly the boson-boson scattering length. We predict the
properties of the generated Faraday patterns and study the parameter regions
where they can be excited.Comment: Final published versio
Portal vein thrombosis following laparoscopic cholecystectomy complicated by dengue viral infection: a case report
<p>Abstract</p> <p>Introduction</p> <p>Portal vein thrombosis is an uncommon post-operative complication following abdominal surgery. Although therapeutic anticoagulation is recommended, this treatment may be questionable when the patient has an associated bleeding diathesis.</p> <p>Case presentation</p> <p>We report a case of a 63-year-old woman of Asian Indian ethnicity who developed portal vein thrombosis following an uneventful laparoscopic cholecystectomy for symptomatic gallstones. Her condition was further complicated by dengue viral infection in the post-operative period, with thrombocytopenia immediately preceding the diagnosis of portal vein thrombosis. The etiological connections between dengue viral infection with thrombocytopenia, laparoscopic cholecystectomy, portal vein thrombosis as well as the treatment dilemmas posed in treating a patient with portal vein thrombosis with a bleeding diathesis are discussed.</p> <p>Conclusion</p> <p>When portal vein thrombosis occurs in patients with contraindications to anticoagulation, there is a role for initial conservative management without aggressive anticoagulation therapy and such patients must be approached on an individualized basis.</p
Currency Unions
A currency union is when several independent sovereign nations share a common currency. This has been a recurring phenomenon in monetary history. In this article I study the theoretical foundations of such unions, and discuss some important currency unions in history, most notably the case of the US. Finally I contrast the design of the EMU with economic theories and historical experiences of currency unions
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