158 research outputs found
Experimental demonstration of fractional orbital angular momentum entanglement of two photons
The singular nature of a non-integer spiral phase plate allows easy
manipulation of spatial degrees of freedom of photon states. Using two such
devices, we have observed very high dimensional (D > 3700) spatial entanglement
of twin photons generated by spontaneous parametric down-conversion.Comment: submitted to Phys. Rev. Let
Tomographic test of Bell's inequality
We present a homodyne detection scheme to verify Bell's inequality on correlated optical beams at the output of a nondegenerate parametric amplifier. Our approach is based on tomographic measurement of the joint detection probabilities, which allows high quantum efficiency at detectors. A self-homodyne scheme is suggested to simplify the experimental set-up
Generation of different Bell states within the SPDC phase-matching bandwidth
We study the frequency-angular lineshape for a phase-matched nonlinear
process producing entangled states and show that there is a continuous variety
of maximally-entangled states generated for different mismatch values within
the natural bandwidth. Detailed considerations are made for two specific
methods of polarization entanglement preparation, based on type-II spontaneous
parametric down-conversion (SPDC) and on SPDC in two subsequent type-I crystals
producing orthogonally polarized photon pairs. It turns out that different Bell
states are produced at the center of the SPDC line and on its slopes,
corresponding to about half-maximum intensity level. These Bell states can be
filtered out by either frequency selection or angular selection, or both. Our
theoretical calculations are confirmed by a series of experiments, performed
for the two above-mentioned schemes of producing polarization-entangled photon
pairs and with two kinds of measurements: frequency-selective and
angular-selective.Comment: submitted for publicatio
Does Clauser-Horne-Shimony-Holt Correlation or Freedman-Clauser Correlation lead to the largest violation of Bell's Inequality?
An inequality is deduced from Einstein's locality and a supplementary
assumption. This inequality defines an experiment which can actually be
performed with present technology to test local realism. Quantum mechanics
violate this inequality a factor of 1.5. In contrast, quantum mechanics
violates previous inequalities (for example, Clauser-Horne-Shimony-Holt
inequality of 1969, Freedman-Clauser inequality of 1972, Clauser-Horne
inequality of 1974) by a factor of . Thus the magnitude of violation
of the inequality derived in this paper is approximately larger than
the magnitude of violation of previous inequalities. This result can be
particularly important for the experimental test of locality.Comment: 15 pages, LaTeX file, no figure
First experimental test of Bell inequalities performed using a non-maximally entangled state
We report on the realisation of a new test of Bell inequalities using the
superposition of type I parametric down conversion produced in two different
non-linear crystals pumped by the same laser, but with different polarisation.
The produced state is non-maximally entangled. We discuss the advantages and
the possible developments of this configuration
Functional Bell inequalities can serve as a stronger entanglement witness
We consider a Bell inequality for a continuous range of settings of the
apparatus at each site. This "functional" Bell inequality gives a better range
of violation for generalized GHZ states. Also a family of N-qubit bound
entangled states violate this inequality for N>5.Comment: 4 pages, REVTeX
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
About Zitterbewegung and electron structure
We start from the spinning electron theory by Barut and Zanghi, which has
been recently translated into the Clifford algebra language. We "complete" such
a translation, first of all, by expressing in the Clifford formalism a
particular Barut-Zanghi (BZ) solution, which refers (at the classical limit) to
an internal helical motion with a time-like speed [and is here shown to
originate from the superposition of positive and negative frequency solutions
of the Dirac equation]. Then, we show how to construct solutions of the Dirac
equation describing helical motions with light-like speed, which meet very well
the standard interpretation of the velocity operator in the Dirac equation
theory (and agree with the solution proposed by Hestenes, on the basis
--however-- of ad-hoc assumptions that are unnecessary in the present
approach). The above results appear to support the conjecture that the
Zitterbewegung motion (a helical motion, at the classical limit) is responsible
for the electron spin.Comment: LaTeX; 11 pages; this is a corrected version of work appeared partly
in Phys. Lett. B318 (1993) 623 and partly in "Particles, Gravity and
Space-Time" (ed.by P.I.Pronin & G.A.Sardanashvily; World Scient., Singapore,
1996), p.34
About entanglement properties of kaons and tests of hidden variables models
In this letter we discuss entanglement properties of neutral kaons systems
and their use for testing local realism. In particular we show that, as
previous proposals, also a scheme recently suggested for performing a test of
hidden variable theories against standard quantum mechanics cannot be
conclusive
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