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ABSTRACT: We report a fully fibered source emitting cross time-bin entangled photons at
1540 nm from type-II spontaneous parametric down conversion. Compared to
standard time-bin entanglement realizations, the preparation interferometer
requires no phase stabilization, simplifying its implementation in quantum key
distribution experiments. Franson/Bell-type tests of such a cross time-bin
state are performed and lead to two-photon interference raw visibilities
greater than 95%, which are only limited by the dark-counts in the detectors
and imperfections in the analysis system. Just by trusting the randomness of
the beam-splitters, the correlations generated by the source can be proved of
non-classical origin even in a passive implementation. The obtained results
confirm the suitability of this source for time-bin based quantum key
distribution.
07/2012;
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ABSTRACT: A Comment on the Letter by Se-Wan Ji et al. [Phys. Rev. Lett. 105, 170404 (2010)]. The authors of the Letter offer a Reply.
Physical Review Letters 05/2011; 106(20):208901; author reply 208902. · 7.37 Impact Factor
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ABSTRACT: The inequalities proposed in [Phys. Rev. Lett. 105, 170404 (2010)] are not
Bell's inequalities in the usual sense: there are local classical models that
violate these inequalities. Thus, their violation demonstrates nonlocality only
under assumptions about the physical implementation and moreover they cannot be
used as a device-independent test of nonlocality.
10/2010;
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ABSTRACT: The only information available about an alleged source of entangled quantum states is the amount S by which the Clauser-Horne-Shimony-Holt inequality is violated: nothing is known about the nature of the system or the measurements that are performed. We discuss how the quality of the source can be assessed in this black-box scenario, as compared to an ideal source that would produce maximally entangled states (more precisely, any state for which S=2√2). To this end, we present several inequivalent notions of fidelity, each one related to the use one can make of the source after having assessed it, and we derive quantitative bounds for each of them in terms of the violation S. We also derive a lower bound on the entanglement of the source as a function of S only.
Phys. Rev. A. 07/2009; 80(6).
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ABSTRACT: We present an entanglement swapping experiment realized for the first time with independent photon pairs created in continuous wave (CW) mode. Pairs of entangled photons are created by the process of spontaneous parametric down conversion in nonlinear periodically poled lithium niobate (PPLN) waveguide crystals. Two photons, one from each pair are combined on a beamsplitter (BS) and projected via a joint measurement onto one of the four Bell states.
Lasers and Electro-Optics, 2007 and the International Quantum Electronics Conference. CLEOE-IQEC 2007. European Conference on; 07/2007
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ABSTRACT: We investigated the preservation of information encoded into the relative phase and amplitudes of optical pulses during storage and retrieval in an optical memory based on stimulated photon echo. By interfering photon echoes produced in a single-mode Ti:Er:LiNbO(3) waveguide, we found that decoherence in the medium translates only as loss and not as degradation of information. We measured a visibility for interfering echoes close to 100%. These results may have important implications for future long-distance quantum communication protocols.
Physical Review Letters 04/2007; 98(11):113601. · 7.37 Impact Factor
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ABSTRACT: Pseudo-telepathy is the most recent form of rejection of locality. Many of its properties have already been discovered: for instance, the minimal entanglement, as well as the minimal cardinality of the output sets, have been characterized. This paper contains two main results. First, we prove that no bipartite pseudo-telepathy game exists, in which one of the partners receives only two questions; as a corollary, we show that the minimal "input cardinality", that is, the minimal number of questions required in a bipartite pseudo-telepathy game, is 3x3. Second, we study the Bell-type inequality derived from the pseudo-telepathy game known as the Magic Square game: we demonstrate that it is a tight inequality for 3 inputs and 4 outputs on each side and discuss its weak resistance to noise.
11/2006;
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ABSTRACT: We show that oblivious transfer can be seen as the classical analogue to a quantum channel in the same sense as non-local boxes are for maximally entangled qubits.
Information Theory Workshop, 2006. ITW '06 Punta del Este. IEEE; 04/2006
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ABSTRACT: Ever since the work of Bell, it has been known that entangled quantum states can rise non-local correlations. However, for almost forty years, it has been assumed that the most non-local states would be the maximally entangled ones. Surprisingly it is not the case: non-maximally entangled states are generally more non-local than maximally entangled states for all the measures of non-locality proposed to date: Bell inequalities, the Kullback-Leibler distance, entanglement simulation with communication or with non-local boxes, the detection loophole and efficiency of cryptography. In fact, one can even find simple examples in low dimensions, confirming that it is not an artefact of a specifically constructed Hilbert space or topology. This anomaly shows that entanglement and non-locality are not only different concepts, but also truly different resources. We review the present knowledge on this anomaly, point out that Hardy's theorem has the same feature, and discuss the perspectives opened by these discoveries.
03/2006;
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ABSTRACT: Correlated photons produced by spontaneous parametric
down-conversion are an essential tool for quantum communication,
especially suited for long-distance connections. To have a
reasonable count rate after all the losses in the propagation and
the filters needed to improve the coherence, it is convenient to
increase the intensity of the laser that pumps the non-linear
crystal. By doing so, however, the importance of the four-photon
component of the down-converted field increases, thus degrading
the quality of two-photon interferences. In this paper, we present
an easy derivation of this nuisance valid for any form of
entanglement generated by down-conversion, followed by a full
study of the problem for time-bin entanglement. We find that the
visibility of two-photon interferences decreases asV=1-2,
where is, in usual situations, the probability per pulse of
creating a detectable photon pair. In particular, the decrease ofV is independent of the coherence of the four-photon term.
Thanks to the fact that can be measured independently ofV, the experimental verification of our prediction is provided
for two different configuration of filters.
The European Physical Journal D 12/2004; 32(1):129-138. · 1.48 Impact Factor
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ABSTRACT: We create pairs of non-degenerate time-bin entangled photons at telecom wavelengths with ultra-short pump pulses. Entanglement is shown by performing Bell kind tests of the Franson type with visibilities of up to 91 time-bin entanglement can easily be protected from decoherence as encountered in optical fibers, this experiment opens the road for complex quantum communication protocols over long distances.
Fortschritte der Physik 04/2003; 51(4‐5):428 - 434. · 1.16 Impact Factor
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ABSTRACT: We create pairs of nondegenerate time-bin entangled photons at telecom wavelengths with ultrashort pump pulses. Entanglement is shown by performing Bell kind tests of the Franson type with visibilities of up to 91%. As time-bin entanglement can easily be protected from decoherence as encountered in optical fibers, this experiment opens the road for complex quantum communication protocols over long distances. We also investigate the creation of more than one photon pair in a laser pulse and present a simple tool to quantify the probability of such events to happen.
Phys. Rev. A. 12/2002; 66(6).
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ABSTRACT: We consider quantum systems composed of $N$ qubits, and the family of all Bell's correlation inequalities for two two-valued measurements per site. We show that if a $N$-qubit state $\rho$ violates any of these inequalities, then it is at least bipartite distillable. Indeed there exists a link between the amount of Bell's inequality violation and the degree of distillability. Thus, we strengthen the interpretation of Bell's inequalities as detectors of useful entanglement. Comment: 6 pages, 3 figures, REVTEX. List of authors extended. Partially rewritten, a rather qualitative explanation of the results. Conclusions unchanged
12/2001;
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ABSTRACT: We consider a family of quantum communication protocols involving N partners. We demonstrate the existence of a link between the security of these protocols against individual attacks by the eavesdropper, and the violation of some Bell's inequalities, generalizing the link that was noticed some years ago for two-partners quantum cryptography. The arguments are independent of the local hidden variable debate.
Physical Review Letters 10/2001; 87(11):117901. · 7.37 Impact Factor
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ABSTRACT: Past, present and future experimental tests of quantum nonlocality are discussed. Consequences of assuming that the state-vector collapse is a real physical phenomenon in space-time are developed. These lead to experiments feasible with today's technology. Comment: 6 pages + 1 Fig. Talk to be presented for the "100 years of Quantum Theory", in the Symposium on "Modern Tests of the Foundations of Quantum Physics", Berlin 11-15 December, 2000
09/2000;
