65 research outputs found
Nonlocality and entanglement in a strange system
We show that the relation between nonlocality and entanglement is subtler
than one naively expects. In order to do this we consider the neutral kaon
system--which is oscillating in time (particle--antiparticle mixing) and
decaying--and describe it as an open quantum system. We consider a Bell--CHSH
inequality and show a novel violation for non--maximally entangled states.
Considering the change of purity and entanglement in time we find that, despite
the fact that only two degrees of freedom at a certain time can be measured,
the neutral kaon system does not behave like a bipartite qubit system.Comment: 7 pages, 2 figures, extended versio
Violation of a Bell inequality in particle physics experimentally verified?
Relevant aspects for testing Bell inequalities with entangled meson-antimeson
systems are analyzed. In particular, we argue that the result of A. Go, J. Mod.
Optics 51, 991 (2004), which nicely illustrate the quantum entanglement of
B-meson pairs, cannot be considered as a Bell-test refuting local realism.Comment: 9 page
Bell inequality and CP violation in the neutral kaon system
For the entangled neutral kaon system we formulate a Bell inequality
sensitive to CP violation in mixing. Via this Bell inequality we obtain a bound
on the leptonic CP asymmetry which is violated by experimental data.
Furthermore, we connect the Bell inequality with a decoherence approach and
find a lower bound on the decoherence parameter which practically corresponds
to Furry's hypothesis.Comment: 10 pages, latex, no figure
Decoherence of entangled kaons and its connection to entanglement measures
We study the time evolution of the entangled kaon system by considering the
Liouville - von Neumann equation with an additional term which allows for
decoherence. We choose as generators of decoherence the projectors to the
2-particle eigenstates of the Hamiltonian. Then we compare this model with the
data of the CPLEAR experiment and find in this way an upper bound on the
strength of the decoherence. We also relate to an effective
decoherence parameter considered previously in literature. Finally we
discuss our model in the light of different measures of entanglement, i.e. the
von Neumann entropy , the entanglement of formation and the concurrence
, and we relate the decoherence parameter to the loss of
entanglement: .Comment: comments and references added, 18 pages, 1 figur
Quantitative complementarity in two-path interferometry
The quantitative formulation of Bohr's complementarity proposed by
Greenberger and Yasin is applied to some physical situations for which
analytical expressions are available. This includes a variety of conventional
double-slit experiments, but also particle oscillations, as in the case of the
neutral-kaon system, and Mott scattering of identical nuclei. For all these
cases, a unified description can be achieved including a new parameter, ,
which quantifies the effective number of fringes one can observe in each
specific interferometric set-up.Comment: 11 RevTex pages, 5 figure
Heisenberg's Uncertainty Relation and Bell Inequalities in High Energy Physics
An effective formalism is developed to handle decaying two-state systems.
Herewith, observables of such systems can be described by a single operator in
the Heisenberg picture. This allows for using the usual framework in quantum
information theory and, hence, to enlighten the quantum feature of such systems
compared to non-decaying systems. We apply it to systems in high energy
physics, i.e. to oscillating meson-antimeson systems. In particular, we discuss
the entropic Heisenberg uncertainty relation for observables measured at
different times at accelerator facilities including the effect of CP violation,
i.e. the imbalance of matter and antimatter. An operator-form of Bell
inequalities for systems in high energy physics is presented, i.e. a
Bell-witness operator, which allows for simple analysis of unstable systems.Comment: 17 page
Dissipation in a 2-dimensional Hilbert space: Various forms of complete positivity
We consider the time evolution of the density matrix in a
2-dimensional complex Hilbert space. We allow for dissipation by adding to the
von Neumann equation a term , which is of Lindblad type in order to
assure complete positivity of the time evolution. We present five equivalent
forms of . In particular, we connect the familiar dissipation matrix
with a geometric version of , where consists of a positive sum
of projectors onto planes in . We also study the minimal number
of Lindblad terms needed to describe the most general case of . All
proofs are worked out comprehensively, as they present at the same time a
practical procedure how to determine explicitly the different forms of
. Finally, we perform a general discussion of the asymptotic behaviour
of the density matrix and we relate the two types of asymptotic
behaviour with our geometric version of .Comment: 11 pages, LaTeX, no figures. Further aspects of complete positivity
worked out and references added; version accepted for publication in Phys.
Lett.
Entanglement, Bell Inequalities and Decoherence in Particle Physics
We demonstrate the relevance of entanglement, Bell inequalities and
decoherence in particle physics. In particular, we study in detail the features
of the ``strange'' system as an example of entangled
meson--antimeson systems. The analogies and differences to entangled spin--1/2
or photon systems are worked, the effects of a unitary time evolution of the
meson system is demonstrated explicitly. After an introduction we present
several types of Bell inequalities and show a remarkable connection to CP
violation. We investigate the stability of entangled quantum systems pursuing
the question how possible decoherence might arise due to the interaction of the
system with its ``environment''. The decoherence is strikingly connected to the
entanglement loss of common entanglement measures. Finally, some outlook of the
field is presented.Comment: Lectures given at Quantum Coherence in Matter: from Quarks to Solids,
42. Internationale Universit\"atswochen f\"ur Theoretische Physik,
Schladming, Austria, Feb. 28 -- March 6, 2004, submitted to Lecture Notes in
Physics, Springer Verlag, 45 page
Hawking Radiation from Non-Extremal D1-D5 Black Hole via Anomalies
We take the method of anomaly cancellation for the derivation of Hawking
radiation initiated by Robinson and Wilczek, and apply it to the non-extremal
five-dimensional D1-D5 black hole in string theory. The fluxes of the electric
charge flow and the energy-momentum tensor from the black hole are obtained.
They are shown to match exactly with those of the two-dimensional black body
radiation at the Hawking temperature.Comment: 14 page
Gravitational anomalies in a dispersive approach
The gravitational anomalies in two dimensions, specifically the Einstein
anomaly and the Weyl anomaly, are fully determined by means of dispersion
relations. In this approach the anomalies originate from the peculiar infrared
feature of the imaginary part of the relevant formfactor which approaches a
-function singularity at zero momentum squared when .Comment: 10 page
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