Realistic limits on the nonlocality of an<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>N</mml:mi></mml:math>-partite single-photon superposition

Laghaout, Amine; Björk, Gunnar; Andersen, Ulrik L.

doi:10.1103/physreva.84.062127

Cited by 9 publications

(14 citation statements)

References 17 publications

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“…Some studies have considered the effect of noise on the non-locality exhibited by multipartite states. It was shown, for instance, that the asymptotic increase in violation of the inequality of [8] with the number of parties is reversed in the presence of decoherence as non-local correlations become increasingly fragile for high number arXiv:1411.4489v1 [quant-ph] 17 Nov 2014 of qubits [21,22]. We see then that indeed sensitivity to noise can drastically affect conclusions concerning non-locality.…”

Section: Introductionmentioning

confidence: 87%

Decoherence effects on the nonlocality of symmetric states

et al. 2015

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The observation of the non-local properties of multipartite entangled states is of great importance for quantum information protocols. Such properties, however, are fragile and may not be observed in the presence of decoherence exhibited by practical physical systems. In this work, we investigate the robustness of the non-locality of symmetric states experiencing phase and amplitude damping, using suitable Bell inequalities based on an extended version of Hardy's paradox. We derive thresholds for observing non-locality in terms of experimental noise parameters, and demonstrate the importance of the choice of the measurement bases for optimizing the robustness. For W states, in the phase damping case, we show that this choice can lead to a trade-off between obtaining a high violation of the non-local test and optimal robustness thresholds; we also show that in this setting the nonlocality of W states is particularly robust for a large number of qubits. Furthermore, we apply our techniques to the discrimination of symmetric states belonging to different entanglement classes, thus illustrating their usefulness for a wide range of practical quantum information applications.

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Section: Introductionmentioning

confidence: 87%

Decoherence effects on the nonlocality of symmetric states

et al. 2015

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“…The list of both fundamental and application-oriented quantum tasks and protocols in a quantum communication setting, i.e., with at least two spatially separated parties sharing classical and quantum resources, can be further extended. There are the fundamental Bell tests, which are to negate local realism even by means of realistic, imperfect detectors, and for this, combined DV and CV measurements may help [130,131]. Gaussian CV entangled states, having an immediate hidden-variable description in form of a positive Wigner function, can never violate a Bell inequality based upon CV homodyne measurements; only the detection of a set of discrete variables such as photon-number parities [132] would work.…”

Section: Quantum Information Processingmentioning

confidence: 99%

Hybrid discrete- and continuous-variable quantum information

et al. 2015

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The development of quantum information processing has traditionally followed two separate and not immediately connected lines of study. The main line has focused on the implementation of quantum bit (qubit) based protocols whereas the other line has been devoted to implementations based on high-dimensional Gaussian states (such as coherent and squeezed states). The separation has been driven by the experimental difficulty in interconnecting the standard technologies of the two lines. However, in recent years, there has been a significant experimental progress in refining and connecting the technologies of the two fields which has resulted in the development and experimental realization of numerous new hybrid protocols. In this Review, we summarize these recent efforts on hybridizing the two types of schemes based on discrete and continuous variables.

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“…Therefore, the limit of 86% derived in [3] should not be directly be compared to our 95% limit, as the latter includes also the inefficiency of the photodetector in an otherwise optimized, unbalanced homodyne receiver when making an x-basis measurement. Therefore, our analysis puts a stricter limit on how efficient the photodetectors need to be [4]. This said, Chaves and Bohr Brask's inequality is more robust against detector inefficiency than that of Heaney et al…”

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confidence: 89%

Erratum: Feasibility of Bell tests with theWstate [Phys. Rev. A81, 033823 (2010)]

Laghaout¹,

Björk²

2012

Phys. Rev. A

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The three-particle Bell inequality, Eq. (11) in [1], as used in our paper reads 1 + P (z i = −1,z j = −1,z k = 1) + P (z i = −1,z j = 1,z k = −1) + P (z i = 1,z j = −1,z k = −1)This interpretation of Eq. (11) in [1] is unfortunately not a true Bell inequality because, for a given mapping of the particle number {1,2,3} onto {i,j,k}, one can find a local hidden variable (LHV) model that violates the inequality. At the time of writing, we believed that while one can find LHV models that violate any specific mapping, one could not, with the same model, violate more than one of the three ensuing inequalities due to different mappings. Thus, if the choice of mapping (and hence the choice of measurement performed) was done outside the light cone (to close the communication loophole), the inequalities would discriminate between LHV and nonlocal models. We have, however, found that this is not true. Denote a LHV preparation of the three particles ), where z 1 = −1 means that if particle 1 is measured in the Z basis, the result is always −1, and if it is instead measured in the X basis, the result x 1 is 1 and so on. Assume the mapping i = 1, j = 2, and k = 3. This preparation has P (z 1 = −1,z 2 = 1,z 3 = −1) = 1, and the rest of the terms in the inequality (1) are zero. Hence, the left-hand side of (1) is 2, a clear violation of the inequality. Due to the i ↔ j symmetry of the inequality, the mapping i = 2, j = 1, and k = 3 gives the same violation of 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 Quantum efficiency η 2 Middle term of Bell's inequality FIG. 4. The sum of the middle terms in (2) as a function of the detector efficiency η 2 for β = 0.71 and measuring the x basis using unbalanced homodyning.the inequality. One also finds that, using this preparation but any of the four remaining mappings {1,2,3} onto {i,j,k}, the left-hand side of the inequality equals unity.Similarly, using the mappings i = 1, j = 3, and k = 2 or i = 3, j = 1, and k = 2 and the preparation ) or the mappings i = 2, j = 3, and k = 1 or i = 3, j = 2, and k = 1 and the preparation

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Realistic limits on the nonlocality of anN-partite single-photon superposition

Cited by 9 publications

References 17 publications

Decoherence effects on the nonlocality of symmetric states

Decoherence effects on the nonlocality of symmetric states

Hybrid discrete- and continuous-variable quantum information

Erratum: Feasibility of Bell tests with theWstate [Phys. Rev. A81, 033823 (2010)]

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