1,937 research outputs found
Charge transfer and coherence dynamics of tunnelling system coupled to a harmonic oscillator
We study the transition probability and coherence of a two-site system,
interacting with an oscillator. Both properties depend on the initial
preparation. The oscillator is prepared in a thermal state and, even though it
cannot be considered as an extended bath, it produces decoherence because of
the large number of states involved in the dynamics. In the case in which the
oscillator is intially displaced a coherent dynamics of change entangled with
oscillator modes takes place. Coherency is however degraded as far as the
oscillator mass increases producing a increasingly large recoherence time.
Calculations are carried on by exact diagonalization and compared with two
semiclassical approximations. The role of the quantum effects are highlighted
in the long-time dynamics, where semiclassical approaches give rise to a
dissipative behaviour. Moreover, we find that the oscillator dynamics has to be
taken into account, even in a semiclassical approximation, in order to
reproduce a thermally activated enhancement of the transition probability
Entanglement properties of spin models in triangular lattices
The different quantum phases appearing in strongly correlated systems as well
as their transitions are closely related to the entanglement shared between
their constituents. In 1D systems, it is well established that the entanglement
spectrum is linked to the symmetries that protect the different quantum phases.
This relation extends even further at the phase transitions where a direct link
associates the entanglement spectrum to the conformal field theory describing
the former. For 2D systems much less is known. The lattice geometry becomes a
crucial aspect to consider when studying entanglement and phase transitions.
Here, we analyze the entanglement properties of triangular spin lattice models
by considering also concepts borrowed from quantum information theory such as
geometric entanglement.Comment: 19 pages, 8 figure
A case study of spin- Heisenberg model in a triangular lattice
We study the spin- model in a triangular lattice in presence of a uniaxial
anisotropy field using a Cluster Mean-Field approach (CMF). The interplay
between antiferromagnetic exchange, lattice geometry and anisotropy forces
Gutzwiller mean-field approaches to fail in a certain region of the phase
diagram. There, the CMF yields two supersolid (SS) phases compatible with those
present in the spin- XXZ model onto which the spin- system maps.
Between these two SS phases, the three-sublattice order is broken and the
results of the CMF depend heavily on the geometry and size of the cluster. We
discuss the possible presence of a spin liquid in this region.Comment: 7 pages, 4 figures, RevTeX 4. The abstract and conclusions have been
modified and the manuscript has been extende
Insights from a Case of Good’s Syndrome (Immunodeficiency with Thymoma)
Immunodeficiency with thymoma was described by R.A. Good in 1954 and is also named after him. The syndrome is characterized by hypogammaglobulinemia associated with thymoma and recurrent infections, bacterial but also viral, fungal and parasitic. Autoimmune diseases, mainly pure red cell aplasia, other hematological disorders and erosive lichen planus are a common finding. We describe here a typical case exhibiting all these clinical features and report a detailed immunophenotypic assessment, as well as the positivity for autoantibodies against three cytokines (IFN-alpha, IL-6 and GM-CSF), which may add to known immune abnormalities. A review of the published literature, based on case series and immunological studies, offers some hints on the still unsolved issues of this rare condition
Mesoscopic continuous and discrete channels for quantum information transfer
We study the possibility of realizing perfect quantum state transfer in
mesoscopic devices. We discuss the case of the Fano-Anderson model extended to
two impurities. For a channel with an infinite number of degrees of freedom, we
obtain coherent behavior in the case of strong coupling or in weak coupling
off-resonance. For a finite number of degrees of freedom, coherent behavior is
associated to weak coupling and resonance conditions
Pretargeted adjuvant radioimmunotherapy with Yttrium-90-biotin in malignant glioma patients: A pilot study
In a previous study we applied a three-step avidin–biotin pretargeting approach to target 90Y-biotin to the tumour in patients with recurrent high grade glioma. The encouraging results obtained in this phase I–II study prompted us to apply the same approach in an adjuvant setting, to evaluate (i) time to relapse and (ii) overall survival. We enrolled 37 high grade glioma patients, 17 with grade III glioma and 20 with glioblastoma, in a controlled open non-randomized study. All patients received surgery and radiotherapy and were disease-free by neuroradiological examinations. Nineteen patients (treated) received adjuvant treatment with radioimmunotherapy. In the treated glioblastoma patients, median disease-free interval was 28 months (range=9–59); median survival was 33.5 months and one patient is still without evidence of disease. All 12 control glioblastoma patients died after a median survival from diagnosis of 8 months. In the treated grade III glioma patients median disease-free interval was 56 months (range=15–60) and survival cannot be calculated as only two, within this group, died. Three-step radioimmunotherapy promises to have an important role as adjuvant treatment in high grade gliomas, particularly in glioblastoma where it impedes progression, prolonging time to relapse and overall survival. A further randomized trial is justified
Two qubits entanglement dynamics in a symmetry-broken environment
We study the temporal evolution of entanglement pertaining to two qubits
interacting with a thermal bath. In particular we consider the simplest
nontrivial spin bath models where symmetry breaking occurs and treat them by
mean field approximation. We analytically find decoherence free entangled
states as well as entangled states with an exponential decay of the quantum
correlation at finite temperature.Comment: 10 pages, 2 figure
Double dot chain as a macroscopic quantum bit
We consider an array of N quantum dot pairs interacting via Coulomb
interaction between adjacent dots and hopping inside each pair. We show that at
the first order in the ratio of hopping and interaction amplitudes, the array
maps in an effective two level system with energy separation becoming
exponentially small in the macroscopic (large N) limit. Decoherence at zero
temperature is studied in the limit of weak coupling with phonons. In this case
the macroscopic limit is robust with respect to decoherence. Some possible
applications in quantum information processing are discussed.Comment: Phys. Rev. A (in press
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