| 1. |
- Ahrens, Johan, et al.
(författare)
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Experimental device independent tests of classical and quantum dimensions
- 2012
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Ingår i: Nature Physics. - 1745-2473 .- 1745-2481. ; 8:8, s. 592-595
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Tidskriftsartikel (refereegranskat)abstract
- A fundamental resource in any communication and computation task is the amount of information that can be transmitted and processed. The classical information encoded in a set of states is limited by the number of distinguishable states or classical dimension d(c) of the set. The sets used in quantum communication and information processing contain states that are neither identical nor distinguishable, and the quantum dimension d(q) of the set is the dimension of the Hilbert space spanned by these states. An important challenge is to assess the (classical or quantum) dimension of a set of states in a device-independent way, that is, without referring to the internal working of the device generating the states. Here we experimentally test dimension witnesses designed to efficiently determine the minimum dimension of sets of (three or four) photonic states from the correlations originated from measurements on them, and distinguish between classical and quantum sets of states.
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| 2. |
- Andersson, Ole, et al.
(författare)
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Device-independent certification of two bits of randomness from one entangled bit and Gisin's elegant Bell inequality
- 2018
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 97:1
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Tidskriftsartikel (refereegranskat)abstract
- We prove that as conjectured by Acín et al. [Phys. Rev. A 93, 040102(R) (2016)], two bits of randomness can be certified in a device-independent way from one bit of entanglement using the maximal quantum violation of Gisin's elegant Bell inequality. This suggests a surprising connection between maximal entanglement, complete sets of mutually unbiased bases, and elements of symmetric informationally complete positive operator-valued measures, on one side, and the optimal way of certifying maximal randomness, on the other.
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| 3. |
- Andersson, Ole, et al.
(författare)
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Self-testing properties of Gisin's elegant Bell inequality
- 2017
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 96:3
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Tidskriftsartikel (refereegranskat)abstract
- An experiment in which the Clauser-Horne-Shimony-Holt inequality is maximally violated is self-testing (i.e., it certifies in a device-independent way both the state and the measurements). We prove that an experiment maximally violating Gisin's elegant Bell inequality is not similarly self-testing. The reason can be traced back to the problem of distinguishing an operator from its complex conjugate. We provide a complete and explicit characterization of all scenarios in which the elegant Bell inequality is maximally violated. This enables us to see exactly how the problem plays out.
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| 4. |
- Badziag, Piotr, et al.
(författare)
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Pentagrams and Paradoxes
- 2011
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Ingår i: FOUNDATIONS OF PHYSICS. - : Springer Science Business Media. - 0015-9018 .- 1572-9516. ; 41:3, s. 414-423
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Tidskriftsartikel (refereegranskat)abstract
- Klyachko and coworkers consider an orthogonality graph in the form of a pentagram, and in this way derive a Kochen-Specker inequality for spin 1 systems. In some low-dimensional situations Hilbert spaces are naturally organised, by a magical choice of basis, into SO(N) orbits. Combining these ideas some very elegant results emerge. We give a careful discussion of the pentagram operator, and then show how the pentagram underlies a number of other quantum "paradoxes", such as that of Hardy.
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| 5. |
- Bengtsson, Ingemar, et al.
(författare)
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Pentagrams and paradoxes
- 2011
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Ingår i: Foundations of Physics. ; 41, s. 414-
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Tidskriftsartikel (refereegranskat)
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| 6. |
- Bengtsson, Ingemar, et al.
(författare)
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Universality of State-Independent Violation of Correlation Inequalities for Non-Contextual Theories
- 2009
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 103:5, s. 050401-
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Tidskriftsartikel (refereegranskat)abstract
- We show that the state-independent violation of inequalities for noncontextual hidden variable theories introduced in [Phys. Rev. Lett. 101, 210401 (2008)] is universal, i.e., occurs for any quantum mechanical system in which noncontextuality is meaningful. We describe a method to obtain state-independent violations for any system of dimension d >= 3. This universality proves that, according to quantum mechanics, there are no "classical'' states.
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| 7. |
- Cabello, Adan, et al.
(författare)
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Simple Hardy-Like Proof of Quantum Contextuality
- 2013
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 111:18, s. 180404-
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Tidskriftsartikel (refereegranskat)abstract
- Contextuality and nonlocality are two fundamental properties of nature. Hardy's proof is considered the simplest proof of nonlocality and can also be seen as a particular violation of the simplest Bell inequality. A fundamental question is: Which is the simplest proof of contextuality? We show that there is a Hardy-like proof of contextuality that can also be seen as a particular violation of the simplest noncontextuality inequality. Interestingly, this new proof connects this inequality with the proof of the Kochen-Specker theorem, providing the missing link between these two fundamental results, and can be extended to an arbitrary odd number n of settings, an extension that can be seen as a particular violation of the n-cycle inequality.
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| 8. |
- Lisonek, Petr, et al.
(författare)
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Kochen-Specker set with seven contexts
- 2014
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 89:4, s. 042101-
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Tidskriftsartikel (refereegranskat)abstract
- The Kochen-Specker (KS) theorem is a central result in quantum theory and has applications in quantum information. Its proof requires several yes-no tests that can be grouped in contexts or subsets of jointly measurable tests. Arguably, the best measure of simplicity of a KS set is the number of contexts. The smaller this number is, the smaller the number of experiments needed to reveal the conflict between quantum theory and noncontextual theories and to get a quantum vs classical outperformance. The original KS set had 132 contexts. Here we introduce a KS set with seven contexts and prove that this is the simplest KS set that admits a symmetric parity proof.
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| 9. |
- Sadiq, Muhammad, et al.
(författare)
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Bell inequalities for the simplest exclusivity graph
- 2013
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 87:1
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Tidskriftsartikel (refereegranskat)abstract
- Which is the simplest logical structure for which there is quantum nonlocality? We show that there are only three bipartite Bell inequalities with quantum violation associated with the simplest graph of relationships of exclusivitywith a quantum-classical gap. These are the most elementary logical Bell inequalities. We showthat the quantum violation of some well-known Bell inequalities is related to them. We test the three Bell inequalities with pairs of polarization-entangled photons and report violations in good agreement with the quantum predictions. Unlike other experiments testing noncontextuality inequalities with pentagonal exclusivity, the ones reported here are free of the compatibility loophole.
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