7,937 research outputs found
Entanglement sudden death and sudden birth in two uncoupled spins
We investigate the entanglement evolution of two qubits interacting with a
common environment trough an Heisenberg XX mechanism. We reveal the possibility
of realizing the phenomenon of entanglement sudden death as well as the
entanglement sudden birth acting on the environment. Such analysis is of
maximal interest at the light of the large applications that spin systems have
in quantum information theory
Interaction-free evolving states of a bipartite system
We show that two interacting physical systems may admit entangled pure or non
separable mixed states evolving in time as if the mutual interaction
hamiltonian were absent. In this paper we define these states Interaction Free
Evolving (IFE) states and characterize their existence for a generic binary
system described by a time independent Hamiltonian. A comparison between IFE
subspace and the decoherence free subspace is reported. The set of all pure IFE
states is explicitly constructed for a non homogeneous spin star system model.Comment: submitted to Phys. Rev.
Elementary symmetric functions of two solvents of a quadratic matrix equation
Quadratic matrix equations occur in a variety of applications. In this paper
we introduce new permutationally invariant functions of two solvents of the n
quadratic matrix equation X^2- L1X - L0 = 0, playing the role of the two
elementary symmetric functions of the two roots of a quadratic scalar equation.
Our results rely on the connection existing between the QME and the theory of
linear second order difference equations with noncommutative coefficients. An
application of our results to a simple physical problem is briefly discussed.Comment: 20 page
state generation of three Josephson qubits in presence of bosonic baths
We analyze an entangling protocol to generate tripartite
Greenberger-Horne-Zeilinger states in a system consisting of three
superconducting qubits with pairwise coupling. The dynamics of the open quantum
system is investigated by taking into account the interaction of each qubit
with an independent bosonic bath with an ohmic spectral structure. To this end
a microscopic master equation is constructed and exactly solved. We find that
the protocol here discussed is stable against decoherence and dissipation due
to the presence of the external baths.Comment: 16 pages and 4 figure
Cell motility: a viscous fingering analysis of active gels
The symmetry breaking of the actin network from radial to longitudinal
symmetry has been identified as the major mechanism for keratocytes (fish
cells) motility on solid substrate. For strong friction coefficient, the two
dimensional actin flow which includes the polymerisation at the edge and
depolymerisation in the bulk can be modelled as a Darcy flow, the cell shape
and dynamics being then modelled by standard complex analysis methods. We use
the theory of active gels to describe the orientational order of the filaments
which varies from the border to the bulk. We show analytically that the
reorganisation of the cortex is enough to explain the motility of the cell and
find the velocity as a function of the orientation order parameter in the bulk.Comment: 15 pages, 4 figures, accepted for publication in EPJ - Plu
W-like states of N uncoupled spins 1/2
The exact dynamics of a disordered spin star system, describing a central
spin coupled to N distinguishable and non interacting spins 1/2, is reported.
Exploiting their interaction with the central single spin system, we present
possible conditional schemes for the generation of W-like states, as well as of
well-defined angular momentum states, of the N uncoupled spins. We provide in
addition a way to estimate the coupling intensity between each of the N spins
and the central one. Finally the feasibility of our procedure is briefly
discussed.Comment: 8 pages, 2 figures, accepted for publication in European Physical
Journal Special Topic
Non-Markovian dissipative dynamics of two coupled qubits in independent reservoirs: a comparison between exact solutions and master equation approaches
The reduced dynamics of two interacting qubits coupled to two independent
bosonic baths is investigated. The one-excitation dynamics is derived and
compared with that based on the resolution of appropriate non-Markovian master
equations. The Nakajima-Zwanzig and the time-convolutionless projection
operator techniques are exploited to provide a description of the non-Markovian
features of the dynamics of the two-qubits system. The validity of such
approximate methods and their range of validity in correspondence to different
choices of the parameters describing the system are brought to light.Comment: 6 pages, 3 figures. Submitted to PR
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