Change search
Refine search result
1 - 20 of 20
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Ahrens, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Amselem, Elias
    Stockholm University, Faculty of Science, Department of Physics.
    Cabello, Adan
    Stockholm University, Faculty of Science, Department of Physics. University of Sevilla, Spain.
    Bourennane, Mohamed
    Stockholm University, Faculty of Science, Department of Physics.
    Two Fundamental Experimental Tests of Nonclassicality with Qutrits2013In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, article id 2170Article in journal (Refereed)
    Abstract [en]

    We report two fundamental experiments on three-level quantum systems (qutrits). The first one tests the simplest task for which quantum mechanics provides an advantage with respect to classical physics. The quantum advantage is certified by the violation of Wright's inequality, the simplest classical inequality violated by quantum mechanics. In the second experiment, we obtain contextual correlations by sequentially measuring pairs of compatible observables on a qutrit, and show the violation of Klyachko et al.'s inequality, the most fundamental noncontextuality inequality violated by qutrits. Our experiment tests exactly Klyachko et al.'s inequality, uses the same measurement procedure for each observable in every context, and implements the sequential measurements in any possible order.

  • 2.
    Ahrens, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Badziag, Piotr
    Stockholm University, Faculty of Science, Department of Physics.
    Cabello, Adan
    Stockholm University, Faculty of Science, Department of Physics. University of Sevilla, Spain.
    Bourennane, Mohamed
    Stockholm University, Faculty of Science, Department of Physics.
    Experimental device independent tests of classical and quantum dimensions2012In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 8, no 8, p. 592-595Article in journal (Refereed)
    Abstract [en]

    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.

  • 3.
    Amselem, Elias
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Danielsen, Lars Eirik
    Lopez-Tarrida, Antonio J.
    Portillo, Jose R.
    Bourennane, Mohamed
    Stockholm University, Faculty of Science, Department of Physics.
    Cabello, Adan
    Stockholm University, Faculty of Science, Department of Physics. University of Sevilla, Spain .
    Experimental fully contextual correlations2012In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 108, no 20, p. 200405-Article in journal (Refereed)
    Abstract [en]

    Quantum correlations are contextual yet, in general, nothing prevents the existence of even more contextual correlations. We identify and test a noncontextuality inequality in which the quantum violation cannot be improved by any hypothetical postquantum theory, and use it to experimentally obtain correlations in which the fraction of noncontextual correlations is less than 0.06. Our correlations are experimentally generated from the results of sequential compatible tests on a four-state quantum system encoded in the polarization and path of a single photon.

  • 4. Aolita, Leandro
    et al.
    Gallego, Rodrigo
    Acin, Antonio
    Chiuri, Andrea
    Vallone, Giuseppe
    Mataloni, Paolo
    Cabello, Adan
    Stockholm University, Faculty of Science, Department of Physics.
    Fully nonlocal quantum correlations2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, no 3, p. 032107-Article in journal (Refereed)
    Abstract [en]

    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.

  • 5. Aolita, Leandro
    et al.
    Gallego, Rodrigo
    Cabello, Adan
    Stockholm University, Faculty of Science, Department of Physics.
    Acin, Antonio
    Fully Nonlocal, Monogamous, and Random Genuinely Multipartite Quantum Correlations2012In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 108, no 10, p. 100401-Article in journal (Refereed)
    Abstract [en]

    Local measurements on bipartite maximally entangled states can yield correlations that are maximally nonlocal, monogamous, and with fully random outcomes. This makes these states ideal for bipartite cryptographic tasks. Genuine-multipartite nonlocality constitutes a stronger notion of nonlocality in the multipartite case. Maximal genuine-multipartite nonlocality, monogamy, and random outcomes are thus highly desired properties for genuine-multipartite cryptographic scenarios. We prove that local measurements on any Greenberger-Horne-Zeilinger state can produce correlations that are fully genuine-multipartite nonlocal, monogamous, and with fully random outcomes. A key ingredient in our proof is a multipartite chained Bell inequality detecting genuine-multipartite nonlocality, which we introduce. Finally, we discuss applications to device-independent secret sharing.

  • 6. Araujo, Mateus
    et al.
    Quintino, Marco Tulio
    Cavalcanti, Daniel
    Santos, Marcelo Franca
    Cabello, Adan
    Stockholm University, Faculty of Science, Department of Physics.
    Cunha, Marcelo Terra
    Tests of bell inequality with arbitrarily low photodetection efficiency and homodyne measurements2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 86, no 3, p. 030101-Article in journal (Refereed)
    Abstract [en]

    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.

  • 7.
    Bengtsson, Ingemar
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Blanchfield, Kate
    Stockholm University, Faculty of Science, Department of Physics.
    Cabello, Adán
    Stockholm University, Faculty of Science, Department of Physics. Universidad de Sevilla, Spain.
    A Kochen-Specker inequality for a SIC2012In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 376, no 4, p. 374-376Article in journal (Refereed)
    Abstract [en]

    Yu and Oh (eprint) [1] have given a state-independent proof of the Kochen–Specker theorem in three dimensions using only 13 rays. The proof consists of showing that a non-contextual hidden variable theory necessarily leads to an inequality that is violated by quantum mechanics. We give a similar proof making use of 21 rays that constitute aSIC (symmetric informationally-complete positive operator-valued measure) and a complete set of MUB (mutually unbiased bases). A theory-independent inequality is also presented using the same 21 rays, as required for experimental tests of contextuality.

  • 8. Budroni, Costantino
    et al.
    Cabello, Adan
    Stockholm University, Faculty of Science, Department of Physics.
    Bell inequalities from variable-elimination methods2012In: Journal of Physics A: Mathematical and Theoretical, ISSN 1751-8113, E-ISSN 1751-8121, Vol. 45, no 38, p. 385304-Article in journal (Refereed)
    Abstract [en]

    Tight Bell inequalities are facets of Pitowsky's correlation polytope and are usually obtained from its extreme points by solving the hull problem. Here, we present an alternative method based on a combination of algebraic results on extensions of measures and variable-elimination methods, e. g., the Fourier-Motzkin method. Our method is shown to overcome some of the computational difficulties associated with the hull problem in some non-trivial cases. Moreover, it provides an explanation for the arising of only a finite number of families of Bell inequalities in measurement scenarios where one experimenter can choose between an arbitrary number of different measurements.

  • 9.
    Cabello, Adan
    Stockholm University, Faculty of Science, Department of Physics. University of Seville, Spain.
    The Contextual Computer2013In: Computable Universe: Understanding and Exploring Nature as Computation / [ed] Zenil, H., Singapore: World Scientific Publishing , 2013, p. 595-604Chapter in book (Refereed)
    Abstract [en]

    What kind of computer is the universe? Here we present three results. The first is a consequence of the Kochen-Specker theorem: If the predictions of quantum mechanics are correct, then the universe cannot be a non-contextual computer. We then show that, if we assume that the density of memory is bounded, then the universe cannot be a classical contextual computer. The third result singles out the universe among all possible contextual computers by exploiting a curious connection with graph theory: In the universe, the maximal contextuality of a set of propositions is given by the Lovasz number of the graph representing their mutual exclusiveness.

  • 10.
    Cabello, Adan
    et al.
    Stockholm University, Faculty of Science, Department of Physics. University of Sevilla, Spain.
    Amselem, Elias
    Stockholm University, Faculty of Science, Department of Physics.
    Blanchfield, Kate
    Stockholm University, Faculty of Science, Department of Physics.
    Bourennane, Mohamed
    Stockholm University, Faculty of Science, Department of Physics.
    Bengtsson, Ingemar
    Stockholm University, Faculty of Science, Department of Physics.
    Proposed experiments of qutrit state-independent contextuality and two-qutrit contextuality-based nonlocality2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, no 3, p. 032108-Article in journal (Refereed)
    Abstract [en]

    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.

  • 11.
    Cabello, Adan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    D'Ambrosio, Vincenzo
    Nagali, Eleonora
    Sciarrino, Fabio
    Hybrid ququart-encoded quantum cryptography protected by Kochen-Specker contextuality2011In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 84, no 3, p. 030302-Article in journal (Refereed)
    Abstract [en]

    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.

  • 12.
    Cabello, Adan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Danielsen, Lars Eirik
    Lopez-Tarrida, Antonio J.
    Portillo, Jose R.
    Quantum social networks2012In: Journal of Physics A: Mathematical and Theoretical, ISSN 1751-8113, E-ISSN 1751-8121, Vol. 45, no 28, p. 285101-Article in journal (Refereed)
    Abstract [en]

    We introduce a physical approach to social networks (SNs) in which each actor is characterized by a yes-no test on a physical system. This allows us to consider SNs beyond those originated by interactions based on pre-existing properties, as in a classical SN (CSN). As an example of SNs beyond CSNs, we introduce quantum SNs (QSNs) in which actor i is characterized by a test of whether or not the system is in a quantum state |psi(i)>. We show that QSNs outperform CSNs for a certain task and some graphs. We identify the simplest of these graphs and show that graphs in which QSNs outperform CSNs are increasingly frequent as the number of vertices increases. We also discuss more general SNs and identify the simplest graphs in which QSNs cannot be outperformed.

  • 13.
    Cabello, Adan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Sciarrino, Fabio
    Loophole-Free Bell Test Based on Local Precertification of Photon's Presence2012In: PHYSICAL REVIEW X, ISSN 2160-3308, Vol. 2, no 2, p. 021010-Article in journal (Refereed)
    Abstract [en]

    A loophole-free violation of Bell inequalities is of fundamental importance for demonstrating quantum nonlocality and long-distance device-independent secure communication. However, transmission losses represent a fundamental limitation for photonic loophole-free Bell tests. A local precertification of the presence of the photons immediately before the local measurements may solve this problem. We show that local precertification is feasible by integrating three current technologies: (i) enhanced single-photon down-conversion to locally create a flag photon, (ii) nanowire-based superconducting single-photon detectors for a fast flag detection, and (iii) superconducting transition-edge sensors to close the detection loophole. We carry out a precise space-time analysis of the proposed scheme, showing its viability and feasibility.

  • 14.
    Cabello, Adán
    Stockholm University, Faculty of Science, Department of Physics.
    Quantum physics: Correlations without parts2011In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 474, no 7352, p. 456-458Article in journal (Refereed)
  • 15. Chen, Jing-Ling
    et al.
    Su, Hong-Yi
    Wu, Chunfeng
    Deng, Dong-Ling
    Cabello, Adan
    Stockholm University, Faculty of Science, Department of Physics.
    Kwek, L. C.
    Oh, C. H.
    Quantum contextuality for a relativistic spin-1/2 particle2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 87, no 2, p. 022109-Article in journal (Refereed)
    Abstract [en]

    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

  • 16. D'Ambrosio, Vincenzo
    et al.
    Herbauts, Isabelle
    Stockholm University, Faculty of Science, Department of Physics.
    Amselem, Elias
    Stockholm University, Faculty of Science, Department of Physics.
    Nagali, Eleonora
    Bourennane, Mohamed
    Stockholm University, Faculty of Science, Department of Physics.
    Sciarrino, Fabio
    Cabello, Adan
    Stockholm University, Faculty of Science, Department of Physics.
    Experimental Implementation of a Kochen-Specker Set of Quantum Tests2013In: Physical Review X, ISSN 2160-3308, E-ISSN 2160-3308, Vol. 3, no 1, p. 011012-Article in journal (Refereed)
    Abstract [en]

    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

  • 17. Kleinmann, Matthias
    et al.
    Guehne, Otfried
    Portillo, Jose R.
    Larsson, Jan-Ake
    Cabello, Adan
    Stockholm University, Faculty of Science, Department of Physics.
    Memory cost of quantum contextuality2011In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 13, p. 113011-Article in journal (Refereed)
    Abstract [en]

    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.

  • 18. Kolenderski, Piotr
    et al.
    Sinha, Urbasi
    Youning, Li
    Zhao, Tong
    Volpini, Matthew
    Cabello, Adan
    Stockholm University, Faculty of Science, Department of Physics.
    Laflamme, Raymond
    Jennewein, Thomas
    Aharon-Vaidman quantum game with a Young-type photonic qutrit2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 86, no 1, p. 012321-Article in journal (Refereed)
    Abstract [en]

    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.

  • 19. Nagali, Eleonora
    et al.
    D'Ambrosio, Vincenzo
    Sciarrino, Fabio
    Cabello, Adan
    Stockholm University, Faculty of Science, Department of Physics.
    Experimental Observation of Impossible-to-Beat Quantum Advantage on a Hybrid Photonic System2012In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 108, no 9, p. 090501-Article in journal (Refereed)
    Abstract [en]

    Quantum resources outperform classical ones for certain communication and computational tasks. Remarkably, in some cases, the quantum advantage cannot be improved using hypothetical postquantum resources. A class of tasks with this property can be singled out using graph theory. Here we report the experimental observation of an impossible-to-beat quantum advantage on a four-dimensional quantum system defined by the polarization and orbital angular momentum of a single photon. The results show pristine evidence of the quantum advantage and are compatible with the maximum advantage allowed using postquantum resources.

  • 20.
    Sadiq, Muhammad
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Badziag, Piotr
    Stockholm University, Faculty of Science, Department of Physics.
    Bourennane, Mohamed
    Stockholm University, Faculty of Science, Department of Physics.
    Cabello, Adán
    Stockholm University, Faculty of Science, Department of Physics. Universidad de Sevilla, Spain.
    Bell inequalities for the simplest exclusivity graph2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 87, no 1, article id 012128Article in journal (Refereed)
    Abstract [en]

    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. DOI: 10.1103/PhysRevA.87.012128

1 - 20 of 20
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf