123 research outputs found
Randomness, Nonlocality and information in entagled correlations
It is shown that the Einstein, Podolsky and Rosen (EPR) correlations for
arbitrary spin-s and the Greenberger, Horne and Zeilinger (GHZ) correlations
for three particles can be described by nonlocal joint and conditional quantum
probabilities. The nonlocality of these probabilities makes the Bell's
inequalities void. A description that exhibits the relation between the
randomness and the nonlocality of entangled correlations is introduced.
Entangled EPR and GHZ correlations are studied using the Gibbs-Shannon entropy.
The nonlocal character of the EPR correlations is tested using the information
Bell's inequalities. Relations between the randomness, the nonlocality and the
entropic information for the EPR and the GHZ correlations are established and
discussed.Comment: 19 pages, REVTEX, 8 figures included in the uuencoded postscript fil
String Entanglement and D-branes as Pure States
We study the entanglement of closed strings degrees of freedom in order to
investigate the microscopic structure and statistics of objects as D-branes. By
considering the macroscopic pure state (MPS) limit, whenever the entanglement
entropy goes to zero (in such a way that the macroscopic properties of the
state are preserved), we show that boundary states may be recovered in this
limit and, furthermore, the description through closed string (perturbative)
degrees of freedom collapses. We also show how the thermal properties of branes
and closed strings could be described by this model, and it requires that
dissipative effects be taken into account. Extensions of the MPS analysis to
more general systems at finite temperature are finally emphasized.Comment: 14 pages. Minor improvements. Published in Phys. Rev.
Depolarization channels with zero-bandwidth noises
A simple model describing depolarization channels with zero-bandwidth
environment is presented and exactly solved. The environment is modelled by
Lorentzian, telegraphic and Gaussian zero-bandwidth noises. Such channels can
go beyond the standard Markov dynamics and therefore can illustrate the
influence of memory effects of the noisy communication channel on the
transmitted information. To quantify the disturbance of quantum states the
entanglement fidelity between arbitrary input and output states is
investigated.Comment: 15 pages, 3 figure
Analysis of complete positivity conditions for quantum qutrit channels
We present an analysis of complete positivity (CP) constraints on qutrit
quantum channels that have a form of affine transformations of generalized
Bloch vector. For diagonal (damping) channels we derive conditions analogous to
the ones that in qubit case produce tetrahedron structure in the channel
parameter space.Comment: 12 pages, 8 figures (.eps), minor changes in the text and formula
Equivalence between two-mode spin squeezed states and pure entangled states with equal spin
We prove that a pure entangled state of two subsystems with equal spin is
equivalent to a two-mode spin-squeezed state under local operations except for
a set of bipartite states with measure zero, and we provide a counterexample to
the generalization of this result to two subsystems of unequal spin.Comment: 6 pages, no figure
Generation and control of resonance states in crossed magnetic and electric fields
A two-dimensional electron system interacting with an impurity and placed in
crossed magnetic and electric fields is under investigation. Since it is
assumed that an impurity center interacts as an attractive -like
potential a renormalization procedure for the retarded Green's function has to
be carried out. For the vanishing electric field we obtain a close analytical
expression for the Green's function and we find one bound state localized
between Landau levels. It is also shown by numerical investigations that
switching on the electric field new long-living resonance states localized in
the vicinity of Landau levels can be generated.Comment: 6 pages, 6 figures, 1 tabl
Finite-Time Disentanglement via Spontaneous Emission
We show that under the influence of pure vacuum noise two entangled qubits
become completely disentangled in a finite time, and in a specific example we
find the time to be given by times the
usual spontaneous lifetime.Comment: revtex, 4 pages, 2 figure
Time-frequency Domain Analogues of Phase Space Sub-Planck Structures
We present experimental data of the frequency resolved optical gating (FROG)
measurements of light pulses revealing interference features corresponding to
sub-Planck structures in phase space. For superpositions of pulses a small,
sub-Fourier shift in the carrier frequency leads to a state orthogonal to the
initial one, although in the representation of standard time-frequency
distributions these states seem to have a nonvanishing overlap.Comment: New title, minor change
Nonlocality of Two-Mode Squeezing with Internal Noise
We examine the quantum states produced through parametric amplification with
internal quantum noise. The internal diffusion arises by coupling both modes of
light to a reservoir for the duration of the interaction time. The Wigner
function for the diffused two-mode squeezed state is calculated. The
nonlocality, separability, and purity of these quantum states of light are
discussed. In addition, we conclude by studying the nonlocality of two other
continuous variable states: the Werner state and the phase-diffused state for
two light modes.Comment: 7 pages, 5 figures, submitted to PR
Improvement of measurement accuracy in SU(1,1) interferometers
We consider an SU(1,1) interferometer employing four-wave mixers that is fed
with two-mode states which are both coherent and intelligent states of the
SU(1,1) Lie group. It is shown that the phase sensitivity of the interferometer
can be essentially improved by using input states with a large photon-number
difference between the modes.Comment: LaTeX, 5 pages, 1 figure (compressed PostScript, available at
http://www.technion.ac.il/~brif/graphics/interfer_graph/qopt.ps.gz ). More
information on http://www.technion.ac.il/~brif/science.htm
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