818 research outputs found
Bi-partite mode entanglement of bosonic condensates on tunneling graph
We study a set of spatial bosonic modes localized on a graph
The particles are allowed to tunnel from vertex to vertex by hopping along the
edges of We analyze how, in the exact many-body eigenstates of the
system i.e., Bose-Einstein condensates over single-particle eigenfunctions, the
bi-partite quantum entanglement of a lattice vertex with respect to the rest of
the graph depends on the topology of Comment: 3 Pages LaTeX, 2 Figures include
Subdecoherent Information Encoding in a Quantum-Dot Array
A potential implementation of quantum-information schemes in semiconductor
nanostructures is studied. To this end, the formal theory of quantum encoding
for avoiding errors is recalled and the existence of noiseless states for model
systems is discussed. Based on this theoretical framework, we analyze the
possibility of designing noiseless quantum codes in realistic semiconductor
structures. In the specific implementation considered, information is encoded
in the lowest energy sector of charge excitations of a linear array of quantum
dots. The decoherence channel considered is electron-phonon coupling We show
that besides the well-known phonon bottleneck, reducing single-qubit
decoherence, suitable many-qubit initial preparation as well as register design
may enhance the decoherence time by several orders of magnitude. This behaviour
stems from the effective one-dimensional character of the phononic environment
in the relevant region of physical parameters.Comment: 12 pages LaTeX, 5 postscript figures. Final version accepted by PR
Quantum Entanglement in Fermionic Lattices
The Fock space of a system of indistinguishable particles is isomorphic (in a
non-unique way) to the state-space of a composite i.e., many-modes, quantum
system. One can then discuss quantum entanglement for fermionic as well as
bosonic systems. We exemplify the use of this notion -central in quantum
information - by studying some e.g., Hubbard,lattice fermionic models relevant
to condensed matter physics.Comment: 4 Pages LaTeX, 1 TeX Figure. Presentation improved, title changed. To
appear in PR
Dynamical Generation of Noiseless Quantum Subsystems
We present control schemes for open quantum systems that combine decoupling
and universal control methods with coding procedures. By exploiting a general
algebraic approach, we show how appropriate encodings of quantum states result
in obtaining universal control over dynamically-generated noise-protected
subsystems with limited control resources. In particular, we provide an
efficient scheme for performing universal encoded quantum computation in a wide
class of systems subjected to linear non-Markovian quantum noise and supporting
Heisenberg-type internal Hamiltonians.Comment: 4 pages, no figures; REVTeX styl
Non-Abelian Geometric Quantum Memory with Atomic Ensemble
We study a quantum information storage scheme based on an atomic ensemble
with near (also exact) three-photon resonance electromagnetically induced
transparency (EIT). Each 4-level-atom is coupled to two classical control
fields and a quantum probe field. Quantum information is adiabatically stored
in the associated dark polariton manifold. An intrinsic non-trivial topological
structure is discovered in our quantum memory implemented through the symmetric
collective atomic excitations with a hidden SU(3) dynamical symmetry. By
adiabatically changing the Rabi frequencies of two classical control fields,
the quantum state can be retrieved up to a non-abelian holonomy and thus
decoded from the final state in a purely geometric way.Comment: 4 pages, 2 figure
The Effect Of Maternal Near Miss On Adverse Infant Nutritional Outcomes
To evaluate the association between self-reported maternal near miss and adverse nutritional status in children under one year of age. METHODS: This study is a secondary analysis of a study in which women who took their children under one year of age to the national vaccine campaign were interviewed. The self-reported condition of maternal near miss used the criteria of Intensive Care Unit admission; eclampsia; blood transfusion and hysterectomy; and their potential associations with any type of nutritional disorder in children, including deficits in weight-for-age, deficits in height-for-age, obesity and breastfeeding. The rates of near miss for the country, regions and states were initially estimated. The relative risks of infant adverse nutritional status according to near miss and maternal/childbirth characteristics were estimated with their 95% CIs using bivariate and multiple analyses. RESULTS: The overall prevalence of near miss was 2.9% and was slightly higher for the Legal Amazon than for other regions. No significant associations were found with nutritional disorders in children. Only a 12% decrease in overall maternal breastfeeding was associated with near miss. Living in the countryside and child over 6 months of age increased the risk of altered nutritional status by approximately 15%, while female child gender decreased this risk by 30%. Maternal near miss was not associated with an increased risk of any alteration in infant nutritional status. CONCLUSIONS: There was no association between maternal near miss and altered nutritional status in children up to one year of age. The risk of infant adverse nutritional status was greater in women living in the countryside, for children over 6 months of age and for male gender.711059359
Multi-distributed Entanglement in Finitely Correlated Chains
The entanglement-sharing properties of an infinite spin-chain are studied
when the state of the chain is a pure, translation-invariant state with a
matrix-product structure. We study the entanglement properties of such states
by means of their finitely correlated structure. These states are recursively
constructed by means of an auxiliary density matrix \rho on a matrix algebra B
and a completely positive map E: A \otimes B -> B, where A is the spin 2\times
2 matrix algebra. General structural results for the infinite chain are
therefore obtained by explicit calculations in (finite) matrix algebras. In
particular, we study not only the entanglement shared by nearest-neighbours,
but also, differently from previous works, the entanglement shared between
connected regions of the spin-chain. This range of possible applications is
illustrated and the maximal concurrence C=1/\sqrt{2} for the entanglement of
connected regions can actually be reached.Comment: 7 pages, 2 figures, to be published in Eur.Phys.Let
Universal Fault-Tolerant Computation on Decoherence-Free Subspaces
A general scheme to perform universal quantum computation within
decoherence-free subspaces (DFSs) of a system's Hilbert space is presented.
This scheme leads to the first fault-tolerant realization of universal quantum
computation on DFSs with the properties that (i) only one- and two-qubit
interactions are required, and (ii) the system remains within the DFS
throughout the entire implementation of a quantum gate. We show explicitly how
to perform universal computation on clusters of the four-qubit DFS encoding one
logical qubit each under "collective decoherence" (qubit-permutation-invariant
system-bath coupling). Our results have immediate relevance to a number of
solid-state quantum computer implementations, in particular those in which
quantum logic is implemented through exchange interactions, such as the
recently proposed spin-spin coupled GaAs quantum dot arrays and the Si:P
nuclear spin arrays.Comment: 5 pages, no figures. Many small changes and clarifications. Expanded
discussion of relevance to solid-state implementations. This version to
appear in Phys. Rev. Let
Quantum phase transitions in the Kondo-necklace model: Perturbative continuous unitary transformation approach
The Kondo-necklace model can describe magnetic low-energy limit of strongly
correlated heavy fermion materials. There exist multiple energy scales in this
model corresponding to each phase of the system. Here, we study quantum phase
transition between the Kondo-singlet phase and the antiferromagnetic long-range
ordered phase, and show the effect of anisotropies in terms of quantum
information properties and vanishing energy gap. We employ the "perturbative
continuous unitary transformations" approach to calculate the energy gap and
spin-spin correlations for the model in the thermodynamic limit of one, two,
and three spatial dimensions as well as for spin ladders. In particular, we
show that the method, although being perturbative, can predict the expected
quantum critical point, where the gap of low-energy spectrum vanishes, which is
in good agreement with results of other numerical and Green's function
analyses. In addition, we employ concurrence, a bipartite entanglement measure,
to study the criticality of the model. Absence of singularities in the
derivative of concurrence in two and three dimensions in the Kondo-necklace
model shows that this model features multipartite entanglement. We also discuss
crossover from the one-dimensional to the two-dimensional model via the ladder
structure.Comment: 12 pages, 6 figure
Effects of environmental parameters to total, quantum and classical correlations
We quantify the total, quantum, and classical correlations with entropic
measures, and quantitatively compare these correlations in a quantum system, as
exemplified by a Heisenberg dimer which is subjected to the change of
environmental parameters: temperature and nonuniform external field. Our
results show that the quantum correlation may exceed the classical correlation
at some nonzero temperatures, though the former is rather fragile than the
later under thermal fluctuation. The effect of the external field to the
classical correlation is quite different from the quantum correlation.Comment: 6 pages, 4 figure
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