| 1. |
- 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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| 2. |
- Aolita, Leandro, et al.
(författare)
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Fully nonlocal quantum correlations
- 2012
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 85:3, s. 032107-
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Tidskriftsartikel (refereegranskat)abstract
- Quantum mechanics is a nonlocal theory, but not as nonlocal as the no-signalling principle allows. However, there exist quantum correlations that exhibit maximal nonlocality: they are as nonlocal as any nonsignalling correlation and thus have a local content, quantified by the fraction p(L) of events admitting a local description, equal to zero. We exploit the known link between the Kochen-Specker and Bell theorems to derive a maximal violation of a Bell inequality from every Kochen-Specker proof. We then show that these Bell inequalities lead to experimental bounds on the local content of quantum correlations that are significantly better than those based on other constructions. We perform the experimental demonstration of a Bell test originating from the Peres-Mermin Kochen-Specker proof, providing an upper bound on the local content pL less than or similar to 0.22.
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| 3. |
- Araujo, Mateus, et al.
(författare)
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Tests of bell inequality with arbitrarily low photodetection efficiency and homodyne measurements
- 2012
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 86:3, s. 030101-
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Tidskriftsartikel (refereegranskat)abstract
- We show that hybrid local measurements combining homodyne measurements and photodetection provide violations of a Bell inequality with arbitrarily low photodetection efficiency. This is shown in two different scenarios: when one part receives an atom entangled to the field mode to be measured by the other part and when both parts make similar photonic measurements. Our findings promote the hybrid measurement scenario as a candidate for loophole-free Bell tests beyond previous expectations.
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| 4. |
- Cabello, Adan, et al.
(författare)
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Hybrid ququart-encoded quantum cryptography protected by Kochen-Specker contextuality
- 2011
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 84:3, s. 030302-
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Tidskriftsartikel (refereegranskat)abstract
- Quantum cryptographic protocols based on complementarity are not secure against attacks in which complementarity is imitated with classical resources. The Kochen-Specker (KS) theorem provides protection against these attacks, without requiring entanglement or spatially separated composite systems. We analyze the maximum tolerated noise to guarantee the security of a KS-protected cryptographic scheme against these attacks and describe a photonic realization of this scheme using hybrid ququarts defined by the polarization and orbital angular momentum of single photons.
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| 5. |
- Cabello, Adan, et al.
(författare)
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Minimum detection efficiency required for a loophole-free violation of the Braunstein-Caves chained Bell inequalities
- 2009
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 79:6, s. 062109-1-062109-7
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Tidskriftsartikel (refereegranskat)abstract
- The chained Bell inequalities of Braunstein and Caves involving N settings per observer have some interesting applications. Here we obtain the minimum detection efficiency required for a loophole-free violation of the Braunstein-Caves inequalities for any N greater than= 2. We discuss both the case in which both particles are detected with the same efficiency and the case in which the particles are detected with different efficiencies.
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| 6. |
- Cabello, Adan, et al.
(författare)
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Proposed experiments of qutrit state-independent contextuality and two-qutrit contextuality-based nonlocality
- 2012
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 85:3, s. 032108-
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Tidskriftsartikel (refereegranskat)abstract
- Recent experiments have demonstrated ququart state-independent quantum contextuality and qutrit state-dependent quantum contextuality. So far, the most basic form of quantum contextuality pointed out by Kochen and Specker, and Bell, has eluded experimental confirmation. Here we present an experimentally feasible test to observe qutrit state-independent quantum contextuality using single photons in a three-path setup. In addition, we show that if the same measurements are performed on two entangled qutrits, rather than sequentially on the same qutrit, then the noncontextual inequality becomes a Bell inequality. We show that this connection also applies to other recently introduced noncontextual inequalities.
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| 7. |
- Chen, Jing-Ling, et al.
(författare)
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Quantum contextuality for a relativistic spin-1/2 particle
- 2013
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 87:2, s. 022109-
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Tidskriftsartikel (refereegranskat)abstract
- The quantum predictions for a single nonrelativistic spin-1/2 particle can be reproduced by noncontextual hidden variables. Here we show that quantum contextuality for a relativistic electron moving in a Coulomb potential naturally emerges if relativistic effects are taken into account. The contextuality can be identified through the violation of noncontextuality inequalities. We also discuss quantum contextuality for the free Dirac electron as well as the relativistic Dirac oscillator. DOI: 10.1103/PhysRevA.87.022109
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| 8. |
- Guehne, Otfried, et al.
(författare)
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Bounding the quantum dimension with contextuality
- 2014
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 89:6
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Tidskriftsartikel (refereegranskat)abstract
- We show that the phenomenon of quantum contextuality can be used to certify lower bounds on the dimension accessed by the measurement devices. To prove this, we derive bounds for different dimensions and scenarios of the simplest noncontextuality inequalities. Some of the resulting dimension witnesses work independently of the prepared quantum state. Our constructions are robust against noise and imperfections, and we show that a recent experiment can be viewed as an implementation of a state-independent quantum dimension witness.
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| 9. |
- Kolenderski, Piotr, et al.
(författare)
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Aharon-Vaidman quantum game with a Young-type photonic qutrit
- 2012
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 86:1, s. 012321-
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Tidskriftsartikel (refereegranskat)abstract
- The Aharon-Vaidman (AV) game exemplifies the advantage of using simple quantum systems to outperform classical strategies. We present an experimental test of this advantage by using a three-state quantum system (qutrit) encoded in a spatial mode of a single photon passing through three slits. The preparation of a particular state is controlled as the photon propagates through the slits by varying the number of open slits and their respective phases. The measurements are achieved by placing detectors in the specific positions in the near and far fields after the slits. This set of tools allowed us to perform tomographic reconstructions of generalized qutrit states, and to implement the quantum version of the AV game with compelling evidence of the quantum advantage.
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| 10. |
- 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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