| 31. |
- 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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| 32. |
- D'Ambrosio, Vincenzo, et al.
(författare)
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Experimental Implementation of a Kochen-Specker Set of Quantum Tests
- 2013
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Ingår i: Physical Review X. - 2160-3308. ; 3:1, s. 011012-
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Tidskriftsartikel (refereegranskat)abstract
- The conflict between classical and quantum physics can be identified through a series of yes-no tests on quantum systems, without it being necessary that these systems be in special quantum states. Kochen-Specker (KS) sets of yes-no tests have this property and provide a quantum-versus-classical advantage that is free of the initialization problem that affects some quantum computers. Here, we report the first experimental implementation of a complete KS set that consists of 18 yes-no tests on four-dimensional quantum systems and show how to use the KS set to obtain a state-independent quantum advantage. We first demonstrate the unique power of this KS set for solving a task while avoiding the problem of state initialization. Such a demonstration is done by showing that, for 28 different quantum states encoded in the orbital-angular-momentum and polarization degrees of freedom of single photons, the KS set provides an impossible-to-beat solution. In a second experiment, we generate maximally contextual quantum correlations by performing compatible sequential measurements of the polarization and path of single photons. In this case, state independence is demonstrated for 15 different initial states. Maximum contextuality and state independence follow from the fact that the sequences of measurements project any initial quantum state onto one of the KS set's eigenstates. Our results show that KS sets can be used for quantum-information processing and quantum computation and pave the way for future developments. DOI: 10.1103/PhysRevX.3.011012
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| 33. |
- Gaertner, Sascha, et al.
(författare)
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Experimental demonstration of a quantum protocol for byzantine agreement and liar detection
- 2008
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 100:7, s. 70504-
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Tidskriftsartikel (refereegranskat)abstract
- We introduce a new quantum protocol for solving detectable Byzantine agreement (also called detectable broadcast) between three parties, and also for solving the detectable liar detection problem. The protocol is suggested by the properties of a four-qubit entangled state, and the classical part of the protocol is simpler than that of previous proposals. In addition, we present an experimental implementation of the protocol using four-photon entanglement.
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| 34. |
- Gonzales-Ureta, Junior R., et al.
(författare)
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Device-independent quantum key distribution based on Bell inequalities with more than two inputs and two outputs
- 2021
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 103:5
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Tidskriftsartikel (refereegranskat)abstract
- Device-independent quantum key distribution (DI-QKD) offers the strongest form of security against eavesdroppers bounded by the laws of quantum mechanics. However, a practical implementation is still pending due to the requirement of combinations of visibility and detection efficiency that are beyond those possible with current technology. This mismatch motivates the search for DI-QKD protocols that can close the gap between theoretical and practical security. In this work, we present two DI-QKD protocols whose security relies on Bell inequalities with more than two inputs and two outputs. We show that, for maximally entangled states and perfect visibility, a protocol based on a Bell inequality with three inputs and four outputs requires a slightly lower detection efficiency than the protocols based on Bell inequalities with two inputs and two outputs.
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| 35. |
- Gonzales-Ureta, Junior R., 1992-, et al.
(författare)
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Optimal and tight Bell inequalities for state-independent contextuality sets
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Two fundamental quantum resources, nonlocality and contextuality, can be connected through Bell inequalities that are violated by state-independent contextuality (SI-C) sets. These Bell inequalities allow for applications requiring simultaneous nonlocality and contextuality. For existing Bell inequalities, the nonlocality produced by SI-C sets is very sensitive to noise. This precludes actual experiments. Here, we identify the Bell inequalities for which the nonlocality produced by SI-C sets is optimal, i.e., maximally robust to either noise or detection inefficiency, for the simplest SI-C [S. Yu and C. H. Oh, Phys. Rev. Lett. 108, 030402 (2012)] and Kochen-Specker sets [A. Cabello et al., Phys. Lett. A 212, 183 (1996)] and show that, in both cases, nonlocality is sufficiently resistant for experiments.
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| 36. |
- 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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| 37. |
- Guehne, Otfried, et al.
(författare)
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Compatibility and noncontextuality for sequential measurements
- 2010
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Ingår i: PHYSICAL REVIEW A. - 1050-2947. ; 81:2, s. 022121-
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Tidskriftsartikel (refereegranskat)abstract
- A basic assumption behind the inequalities used for testing noncontextual hidden variable models is that the observables measured on the same individual system are perfectly compatible. However, compatibility is not perfect in actual experiments using sequential measurements. We discuss the resulting "compatibility loophole" and present several methods to rule out certain hidden variable models that obey a kind of extended noncontextuality. Finally, we present a detailed analysis of experimental imperfections in a recent trapped-ion experiment and apply our analysis to that case.
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| 38. |
- Jogenfors, Jonathan, 1988-, et al.
(författare)
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Comment on "Franson Interference Generated by a Two-Level System"
- 2017
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In a recent Letter [Phys. Rev. Lett. 118, 030501 (2017)], Peiris, Konthasinghe, and Muller report a Franson interferometry experiment using pairs of photons generated from a two-level semiconductor quantum dot. The authors report a visibility of 66% and claim that this visibility “goes beyond the classical limit of 50% and approaches the limit of violation of Bell’s inequalities (70.7%).” We explain why we do not agree with this last statement and how to fix the problem.
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| 39. |
- Kleinmann, Matthias, et al.
(författare)
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Memory cost of quantum contextuality
- 2011
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Ingår i: New Journal of Physics. - : Institute of Physics. - 1367-2630. ; 13:113011
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Tidskriftsartikel (refereegranskat)abstract
- The simulation of quantum effects requires certain classical resources, and quantifying them is an important step to characterize the difference between quantum and classical physics. For a simulation of the phenomenon of state-independent quantum contextuality, we show that the minimum amount of memory used by the simulation is the critical resource. We derive optimal simulation strategies for important cases and prove that reproducing the results of sequential measurements on a two-qubit system requires more memory than the information-carrying capacity of the system.
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| 40. |
- Kleinmann, Matthias, et al.
(författare)
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Optimal Inequalities for State-Independent Contextuality
- 2012
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 109:25, s. 250402-
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Tidskriftsartikel (refereegranskat)abstract
- Contextuality is a natural generalization of nonlocality which does not need composite systems or spacelike separation and offers a wider spectrum of interesting phenomena. Most notably, in quantum mechanics there exist scenarios where the contextual behavior is independent of the quantum state. We show that the quest for an optimal inequality separating quantum from classical noncontextual correlations in a state-independent manner admits an exact solution, as it can be formulated as a linear program. We introduce the noncontextuality polytope as a generalization of the locality polytope and apply our method to identify two different tight optimal inequalities for the most fundamental quantum scenario with state-independent contextuality.
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