36 research outputs found
Witnessing Entanglement with Second-Order Interference and Stokes Parameters
We propose to use Stokes parameter as an entanglement witness for correlated
EPR mixed states of light. Such states can be generated with a beam splitter
acting on two mixed squeezed states of light. Stokes witness operators are
closely related to the Hanbury-Brown and Twiss interference and can be used to
test entanglement in balanced homodyne experiments involving fluctuations of
quantum quadratures of the electric field.Comment: 10 pages, 2 figur
Effective generation of cat and kitten states
We present an effective method of coherent state superposition (cat state)
generation using single trapped ion in a Paul trap. The method is
experimentally feasible for coherent states with amplitude using
available technology. It works both in and beyond the Lamb-Dicke regime.Comment: 11 pages, 8 figure
Witnessing Entanglement with Second-Order Interference
Second-order interference and Hanbury-Brown and Twiss type experiments can
provide an operational framework for the construction of witness operators that
can test classical and nonclassical properties of a Gaussian squeezed state
(GSS), and provide entanglement witness operators to study the separability
properties of correlated Gaussian squeezed sates.Comment: 10 pages, 12 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
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
Witnessing Entanglement of EPR States With Second-Order Interference
The separability of the continuous-variable EPR state can be tested with
Hanbury-Brown and Twiss type interference. The second-order visibility of such
interference can provide an experimental test of entanglement. It is shown that
time-resolved interference leads to the Hong, Ou and Mandel deep, that provides
a signature of quantum non-separability for pure and mixed EPR states. A
Hanbury-Brown and Twiss type witness operator can be constructed to test the
quantum nature of the EPR entanglement.Comment: 9 pages, 5 figure
Classical phase-space descriptions of continuous-variable teleportation
The nonnegative Wigner function of all quantum states involved in
teleportation of Gaussian states using the standard continuous-variable
teleportation protocol means that there is a local realistic phase-space
description of the process. This includes the coherent states teleported up to
now in experiments. We extend the phase-space description to teleportation of
non-Gaussian states using the standard protocol and conclude that teleportation
of non-Gaussian states with fidelity of 2/3 is a "gold standard" for this kind
of teleportation.Comment: New version contains minor changes requested by journal referee
Bloch Equations and Completely Positive Maps
The phenomenological dissipation of the Bloch equations is reexamined in the
context of completely positive maps. Such maps occur if the dissipation arises
from a reduction of a unitary evolution of a system coupled to a reservoir. In
such a case the reduced dynamics for the system alone will always yield
completely positive maps of the density operator. We show that, for Markovian
Bloch maps, the requirement of complete positivity imposes some Bloch
inequalities on the phenomenological damping constants. For non-Markovian Bloch
maps some kind of Bloch inequalities involving eigenvalues of the damping basis
can be established as well. As an illustration of these general properties we
use the depolarizing channel with white and colored stochastic noise.Comment: Talk given at the Conference "Quantum Challenges", Falenty, Poland,
September 4-7, 2003. 21 pages, 3 figure