868 research outputs found
Weight, volume, and center of mass of segments of the human body
Weight, volume, and center of mass of segments of human bod
Is Quantum Mechanics Compatible with a Deterministic Universe? Two Interpretations of Quantum Probabilities
Two problems will be considered: the question of hidden parameters and the
problem of Kolmogorovity of quantum probabilities. Both of them will be
analyzed from the point of view of two distinct understandings of quantum
mechanical probabilities. Our analysis will be focused, as a particular
example, on the Aspect-type EPR experiment. It will be shown that the quantum
mechanical probabilities appearing in this experiment can be consistently
understood as conditional probabilities without any paradoxical consequences.
Therefore, nothing implies in the Aspect experiment that quantum theory is
incompatible with a deterministic universe.Comment: REVISED VERSION! ONLY SMALL CHANGES IN THE TEXT! compressed and
uuencoded postscript, a uuencoded version of a demo program file (epr.exe for
DOS) is attached as a "Figure
General criterion for the entanglement of two indistinguishable particles
We relate the notion of entanglement for quantum systems composed of two
identical constituents to the impossibility of attributing a complete set of
properties to both particles. This implies definite constraints on the
mathematical form of the state vector associated with the whole system. We then
analyze separately the cases of fermion and boson systems, and we show how the
consideration of both the Slater-Schmidt number of the fermionic and bosonic
analog of the Schmidt decomposition of the global state vector and the von
Neumann entropy of the one-particle reduced density operators can supply us
with a consistent criterion for detecting entanglement. In particular, the
consideration of the von Neumann entropy is particularly useful in deciding
whether the correlations of the considered states are simply due to the
indistinguishability of the particles involved or are a genuine manifestation
of the entanglement. The treatment leads to a full clarification of the subtle
aspects of entanglement of two identical constituents which have been a source
of embarrassment and of serious misunderstandings in the recent literature.Comment: 18 pages, Latex; revised version: Section 3.2 rewritten, new Theorems
added, reference [1] corrected. To appear on Phys.Rev.A 70, (2004
Entropy inequalities and Bell inequalities for two-qubit systems
Sufficient conditions for (the non-violation of) the Bell-CHSH inequalities
in a mixed state of a two-qubit system are: 1) The linear entropy of the state
is not smaller than 0.5, 2) The sum of the conditional linear entropies is
non-negative, 3) The von Neumann entropy is not smaller than 0.833, 4) The sum
of the conditional von Neumann entropies is not smaller than 0.280.Comment: Errors corrected. See L. Jakobcyk, quant-ph/040908
Atomic vapor-based high efficiency optical detectors with photon number resolution
We propose a novel approach to the important fundamental problem of detecting
weak optical fields at the few photon level. The ability to detect with high
efficiency (>99%), and to distinguish the number of photons in a given time
interval is a very challenging technical problem with enormous potential
pay-offs in quantum communications and information processing. Our proposal
diverges from standard solid-state photo-detector technology by employing an
atomic vapor as the active medium, prepared in a specific quantum state using
laser radiation. The absorption of a photon will be aided by a dressing laser,
and the presence or absence of an excited atom will be detected using the
``cycling transition'' approach perfected for ion traps. By first incorporating
an appropriate upconversion scheme, our method can be applied to a wide variety
of optical wavelengths.Comment: 4 pages, 2 figure
Comment on "Nonlocality of a Single Photon"
A Comment on the Letter by S. M. Tan, D. F. Walls, and M. J. Collett, Phys. Rev. Lett. 66, 252 (1991)
Proof of Kolmogorovian Censorship
Many argued (Accardi and Fedullo, Pitowsky) that Kolmogorov's axioms of
classical probability theory are incompatible with quantum probabilities, and
this is the reason for the violation of Bell's inequalities. Szab\'o showed
that, in fact, these inequalities are not violated by the experimentally
observed frequencies if we consider the real, ``effective'' frequencies. We
prove in this work a theorem which generalizes this result: ``effective''
frequencies associated to quantum events always admit a Kolmogorovian
representation, when these events are collected through different experimental
set ups, the choice of which obeys a classical distribution.Comment: 19 pages, LaTe
New optimal tests of quantum nonlocality
We explore correlation polytopes to derive a set of all Boole-Bell type
conditions of possible classical experience which are both maximal and
complete. These are compared with the respective quantum expressions for the
Greenberger-Horne-Zeilinger (GHZ) case and for two particles with spin state
measurements along three directions.Comment: 10 page
Non-Contextual Hidden Variables and Physical Measurements
For a hidden variable theory to be indistinguishable from quantum theory for
finite precision measurements, it is enough that its predictions agree for some
measurement within the range of precision. Meyer has recently pointed out that
the Kochen-Specker theorem, which demonstrates the impossibility of a
deterministic hidden variable description of ideal spin measurements on a spin
1 particle, can thus be effectively nullified if only finite precision
measurements are considered. We generalise this result: it is possible to
ascribe consistent outcomes to a dense subset of the set of projection valued
measurements, or to a dense subset of the set of positive operator valued
measurements, on any finite dimensional system. Hence no Kochen-Specker like
contradiction can rule out hidden variable theories indistinguishable from
quantum theory by finite precision measurements in either class.Comment: Typo corrected. Final version: to appear in Phys. Rev. Let
Jamming non-local quantum correlations
We present a possible scheme to tamper with non-local quantum correlations in
a way that is consistent with relativistic causality, but goes beyond quantum
mechanics. A non-local ``jamming" mechanism, operating within a certain
space-time window, would not violate relativistic causality and would not lead
to contradictory causal loops. The results presented in this Letter do not
depend on any model of how quantum correlations arise and apply to any jamming
mechanism.Comment: 10 pp, LaTe
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