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Abellán, C., Acín, A., Alarcón, A., Alibart, O., Andersen, C. K., Andreoli, F., . . . Zhong, J. (2018). Challenging Local Realism with Human Choices. Nature, 557, 212-216
Open this publication in new window or tab >>Challenging Local Realism with Human Choices
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2018 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 557, p. 212-216Article in journal (Refereed) Published
Abstract [en]

A Bell test is a randomized trial that compares experimental observations against the philosophical worldview of local realism , in which the properties of the physical world are independent of our observation of them and no signal travels faster than light. A Bell test requires spatially distributed entanglement, fast and high-efficiency detection and unpredictable measurement settings. Although technology can satisfy the first two of these requirements, the use of physical devices to choose settings in a Bell test involves making assumptions about the physics that one aims to test. Bell himself noted this weakness in using physical setting choices and argued that human ‘free will’ could be used rigorously to ensure unpredictability in Bell tests. Here we report a set of local-realism tests using human choices, which avoids assumptions about predictability in physics. We recruited about 100,000 human participants to play an online video game that incentivizes fast, sustained input of unpredictable selections and illustrates Bell-test methodology. The participants generated 97,347,490 binary choices, which were directed via a scalable web platform to 12 laboratories on five continents, where 13 experiments tested local realism using photons, single atoms, atomic ensembles and superconducting devices. Over a 12-hour period on 30 November 2016, participants worldwide provided a sustained data flow of over 1,000 bits per second to the experiments, which used different human-generated data to choose each measurement setting. The observed correlations strongly contradict local realism and other realistic positions in bi-partite and tri-partite 12 scenarios. Project outcomes include closing the ‘freedom-of-choice loophole’ (the possibility that the setting choices are influenced by ‘hidden variables’ to correlate with the particle properties), the utilization of video-game methods for rapid collection of human-generated randomness, and the use of networking techniques for global participation in experimental science.

Place, publisher, year, edition, pages
Nature Publishing Group, 2018
National Category
Natural Sciences Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-147999 (URN)10.1038/s41586-018-0085-3 (DOI)000431775100044 ()29743691 (PubMedID)2-s2.0-85046623429 (Scopus ID)
Available from: 2018-05-23 Created: 2018-05-23 Last updated: 2018-05-30Bibliographically approved
Jogenfors, J., Adán, C. & Larsson, J.-Å. (2017). Comment on "Franson Interference Generated by a Two-Level System". Ithaca, New York, USA: Cornell University Press
Open this publication in new window or tab >>Comment on "Franson Interference Generated by a Two-Level System"
2017 (English)Other (Other academic)
Abstract [en]

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.

Place, publisher, year, pages
Ithaca, New York, USA: Cornell University Press, 2017. p. 1
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:liu:diva-142073 (URN)
Available from: 2017-10-20 Created: 2017-10-20 Last updated: 2017-10-20
Pacher, C., Abidin, A., Lorünser, T., Peev, M., Ursin, R., Zeilinger, A. & Larsson, J.-Å. (2016). Attacks on quantum key distribution protocols that employ non-ITS authentication. Quantum Information Processing, 15(1), 327-362
Open this publication in new window or tab >>Attacks on quantum key distribution protocols that employ non-ITS authentication
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2016 (English)In: Quantum Information Processing, ISSN 1570-0755, E-ISSN 1573-1332, Vol. 15, no 1, p. 327-362Article in journal (Refereed) Published
Abstract [en]

We demonstrate how adversaries with unbounded computing resources can break Quantum Key Distribution (QKD) protocols which employ a particular message authentication code suggested previously. This authentication code, featuring low key consumption, is not Information-Theoretically Secure (ITS) since for each message the eavesdropper has intercepted she is able to send a different message from a set of messages that she can calculate by finding collisions of a cryptographic hash function. However, when this authentication code was introduced it was shown to prevent straightforward Man-In-The-Middle (MITM) attacks against QKD protocols.

In this paper, we prove that the set of messages that collide with any given message under this authentication code contains with high probability a message that has small Hamming distance to any other given message. Based on this fact we present extended MITM attacks against different versions of BB84 QKD protocols using the addressed authentication code; for three protocols we describe every single action taken by the adversary. For all protocols the adversary can obtain complete knowledge of the key, and for most protocols her success probability in doing so approaches unity.

Since the attacks work against all authentication methods which allow to calculate colliding messages, the underlying building blocks of the presented attacks expose the potential pitfalls arising as a consequence of non-ITS authentication in QKDpostprocessing. We propose countermeasures, increasing the eavesdroppers demand for computational power, and also prove necessary and sufficient conditions for upgrading the discussed authentication code to the ITS level.

Place, publisher, year, edition, pages
Springer Publishing Company, 2016
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-91260 (URN)10.1007/s11128-015-1160-4 (DOI)000372876800020 ()
Projects
ICG QC
Note

Vid tiden för disputation förelåg publikationen som manuskript

Funding agencies: Vienna Science and Technology Fund (WWTF) [ICT10-067]; Austrian Research Promotion Agency (FFG) [Bridge-2364544]

Available from: 2013-04-18 Created: 2013-04-18 Last updated: 2017-12-06Bibliographically approved
Hiesmayr, B. C. & Larsson, J.-Å. (2016). Contextuality and nonlocality in decaying multipartite systems. Physical Review A. Atomic, Molecular, and Optical Physics, 93(2), 020106
Open this publication in new window or tab >>Contextuality and nonlocality in decaying multipartite systems
2016 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 93, no 2, p. 020106-Article in journal (Refereed) Published
Abstract [en]

Everyday experience supports the existence of physical properties independent of observation in strong contrast to the predictions of quantum theory. In particular, the existence of physical properties that are independent of the measurement context is prohibited for certain quantum systems. This property is known as contextuality. This Rapid Communication studies whether the process of decay in space-time generally destroys the ability of revealing contextuality. We find that in the most general situation the decay property does not diminish this ability. However, applying certain constraints due to the space-time structure either on the time evolution of the decaying system or on the measurement procedure, the criteria revealing contextuality become inherently dependent on the decay property or an impossibility. In particular, we derive how the context-revealing setup known as Bells nonlocality tests changes for decaying quantum systems. Our findings illustrate the interdependence between hidden and local hidden parameter theories and the role of time.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2016
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-126838 (URN)10.1103/PhysRevA.93.020106 (DOI)000371389100001 ()
Note

Funding Agencies|Austrian Science Fund [FWF-P26783]

Available from: 2016-04-05 Created: 2016-04-05 Last updated: 2017-11-30
Kofler, J., Giustina, M., Larsson, J.-Å. & Mitchell, M. W. (2016). Requirements for a loophole-free photonic Bell test using imperfect setting generators. Physical Review A. Atomic, Molecular, and Optical Physics, 93(3), 032115
Open this publication in new window or tab >>Requirements for a loophole-free photonic Bell test using imperfect setting generators
2016 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 93, no 3, p. 032115-Article in journal (Refereed) Published
Abstract [en]

Experimental violations of Bell inequalities are in general vulnerable to so-called loopholes. In this work, we analyze the characteristics of a loophole-free Bell test with photons, closing simultaneously the locality, freedom-of-choice, fair-sampling (i.e., detection), coincidence-time, and memory loopholes. We pay special attention to the effect of excess predictability in the setting choices due to nonideal random-number generators. We discuss necessary adaptations of the Clauser-Horne and Eberhard inequality when using such imperfect devices and-using Hoeffdings inequality and Doobs optional stopping theorem-the statistical analysis in such Bell tests.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2016
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-126806 (URN)10.1103/PhysRevA.93.032115 (DOI)000371726700001 ()
Note

Funding Agencies|EU Integrated Project SIQS; SFB; CoQuS program of the FWF (Austrian Science Fund); Austrian Ministry of Science, Research and Economy through the program QUESS; European Research Council [280169]; European Union [641122]; Spanish MINECO [SEV-2015-0522]; MAGO [FIS2011-23520]; EPEC [FIS2014-62181-EXP]; Catalan AGAUR SGR Grant [1295]; Fundacio Privada CELLEX

Available from: 2016-04-07 Created: 2016-04-05 Last updated: 2017-11-30
Dzhafarov, E. N., Kujala, J. V. & Larsson, J.-Å. (2015). Contextuality in Three Types of Quantum-Mechanical Systems. Foundations of physics, 45(7), 762-782
Open this publication in new window or tab >>Contextuality in Three Types of Quantum-Mechanical Systems
2015 (English)In: Foundations of physics, ISSN 0015-9018, E-ISSN 1572-9516, Vol. 45, no 7, p. 762-782Article in journal (Refereed) Published
Abstract [en]

We present a formal theory of contextuality for a set of random variables grouped into different subsets (contexts) corresponding to different, mutually incompatible conditions. Within each context the random variables are jointly distributed, but across different contexts they are stochastically unrelated. The theory of contextuality is based on the analysis of the extent to which some of these random variables can be viewed as preserving their identity across different contexts when one considers all possible joint distributions imposed on the entire set of the random variables. We illustrate the theory on three systems of traditional interest in quantum physics (and also in non-physical, e.g., behavioral studies). These are systems of the Klyachko-Can-Binicioglu-Shumovsky-type, Einstein-Podolsky-Rosen-Bell-type, and Suppes-Zanotti-Leggett-Garg-type. Listed in this order, each of them is formally a special case of the previous one. For each of them we derive necessary and sufficient conditions for contextuality while allowing for experimental errors and contextual biases or signaling. Based on the same principles that underly these derivations we also propose a measure for the degree of contextuality and compute it for the three systems in question.

Place, publisher, year, edition, pages
Springer Verlag (Germany), 2015
Keywords
CHSH inequalities; Contextuality; Klyachko inequalities; Leggett-Garg inequalities; Probabilistic couplings; Signaling
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-120035 (URN)10.1007/s10701-015-9882-9 (DOI)000356263600006 ()
Note

Funding Agencies|NSF [SES-1155956]; AFOSR [FA9550-14-1-0318]

Available from: 2015-07-06 Created: 2015-07-06 Last updated: 2017-12-04
Jogenfors, J., Elhassan, A. M., Ahrens, J., Bourennane, M. & Larsson, J.-Å. (2015). Hacking the Bell test using classical light in energy-time entanglement–based quantum key distribution. Science Advances, 1(11), 1-7, Article ID e1500793.
Open this publication in new window or tab >>Hacking the Bell test using classical light in energy-time entanglement–based quantum key distribution
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2015 (English)In: Science Advances, ISSN 2375-2548, Vol. 1, no 11, p. 1-7, article id e1500793Article in journal (Refereed) Published
Abstract [en]

Photonic systems based on energy-time entanglement have been proposed to test local realism using the Bell inequality. A violation of this inequality normally also certifies security of device-independent quantum key distribution (QKD) so that an attacker cannot eavesdrop or control the system. We show how this security test can be circumvented in energy-time entangled systems when using standard avalanche photodetectors, allowing an attacker to compromise the system without leaving a trace. We reach Bell values up to 3.63 at 97.6% faked detector efficiency using tailored pulses of classical light, which exceeds even the quantum prediction. This is the first demonstration of a violation-faking source that gives both tunable violation and high faked detector efficiency. The implications are severe: the standard Clauser-Horne-Shimony-Holt inequality cannot be used to show device-independent security for energy-time entanglement setups based on Franson’s configuration. However, device-independent security can be reestablished, and we conclude by listing a number of improved tests and experimental setups that would protect against all current and future attacks of this type.

Place, publisher, year, edition, pages
American Association for the Advancement of Science, 2015
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-114210 (URN)10.1126/sciadv.1500793 (DOI)000216604200020 ()
Note

At the time for thesis presentation publication was in status: Manuscript

At the time for thesis presentation name of publication was: A Classical-Light Attack on Energy-Time Entangled Quantum Key Distribution, and Countermeasures

Available from: 2015-02-13 Created: 2015-02-13 Last updated: 2018-03-09Bibliographically approved
Kujala, J. V., Dzhafarov, E. N. & Larsson, J.-Å. (2015). Necessary and Sufficient Conditions for an Extended Noncontextuality in a Broad Class of Quantum Mechanical Systems. Physical Review Letters, 115(15), 150401
Open this publication in new window or tab >>Necessary and Sufficient Conditions for an Extended Noncontextuality in a Broad Class of Quantum Mechanical Systems
2015 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 115, no 15, p. 150401-Article in journal (Refereed) Published
Abstract [en]

The notion of (non) contextuality pertains to sets of properties measured one subset (context) at a time. We extend this notion to include so-called inconsistently connected systems, in which the measurements of a given property in different contexts may have different distributions, due to contextual biases in experimental design or physical interactions (signaling): a system of measurements has a maximally noncontextual description if they can be imposed a joint distribution on in which the measurements of any one property in different contexts are equal to each other with the maximal probability allowed by their different distributions. We derive necessary and sufficient conditions for the existence of such a description in a broad class of systems including Klyachko-Can-Binicioglu-Shumvosky-type (KCBS), EPR-Bell-type, and Leggett-Garg-type systems. Because these conditions allow for inconsistent connectedness, they are applicable to real experiments. We illustrate this by analyzing an experiment by Lapkiewicz and colleagues aimed at testing contextuality in a KCBS-type system.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2015
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-122195 (URN)10.1103/PhysRevLett.115.150401 (DOI)000362337200001 ()
Note

Funding Agencies|NSF [SES-1155956]; AFOSR [FA9550-14-1-0318]; A. von Humboldt Foundation; FQXi through the Silicon Valley Community Foundation

Available from: 2015-10-26 Created: 2015-10-23 Last updated: 2017-12-01
Carvacho, G., Carine, J., Saavedra, G., Cuevas, A., Fuenzalida, J., Toledo, F., . . . Xavier, G. B. (2015). Postselection-Loophole-Free Bell Test Over an Installed Optical Fiber Network. Physical Review Letters, 115(3), 030503
Open this publication in new window or tab >>Postselection-Loophole-Free Bell Test Over an Installed Optical Fiber Network
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2015 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 115, no 3, p. 030503-Article in journal (Refereed) Published
Abstract [en]

Device-independent quantum communication will require a loophole-free violation of Bell inequalities. In typical scenarios where line of sight between the communicating parties is not available, it is convenient to use energy-time entangled photons due to intrinsic robustness while propagating over optical fibers. Here we show an energy-time Clauser-Horne-Shimony-Holt Bell inequality violation with two parties separated by 3.7 km over the deployed optical fiber network belonging to the University of Concepcion in Chile. Remarkably, this is the first Bell violation with spatially separated parties that is free of the postselection loophole, which affected all previous in-field long-distance energy-time experiments. Our work takes a further step towards a fiber-based loophole-free Bell test, which is highly desired for secure quantum communication due to the widespread existing telecommunication infrastructure.

Place, publisher, year, edition, pages
American Physical Society, 2015
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-120450 (URN)10.1103/PhysRevLett.115.030503 (DOI)000357864800002 ()
Note

Funding Agencies|CONICYT [PFB08-024]; Milenio [RC130001]; FONDECYT [11110115, 1150101, 1120067, 1151278]; MINECO, Spain [FIS2011-29400]; FEDER funds; FQXi large grant; CENIIT at Linkoping University; CONICYT; program Science without Borders (CAPES); program Science without Borders (CNPq, Brazil); QWAD-Quantum Waveguides Application and Development [FP7-ICT-2011-9- 600838]

Available from: 2015-08-12 Created: 2015-08-11 Last updated: 2017-12-04
Giustina, M., Versteegh, M. A. M., Wengerowsky, S., Handsteiner, J., Hochrainer, A., Phelan, K., . . . Zeilinger, A. (2015). Significant-Loophole-Free Test of Bells Theorem with Entangled Photons. Physical Review Letters, 115(25), 250401
Open this publication in new window or tab >>Significant-Loophole-Free Test of Bells Theorem with Entangled Photons
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2015 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 115, no 25, p. 250401-Article in journal (Refereed) Published
Abstract [en]

Local realism is the worldview in which physical properties of objects exist independently of measurement and where physical influences cannot travel faster than the speed of light. Bells theorem states that this worldview is incompatible with the predictions of quantum mechanics, as is expressed in Bells inequalities. Previous experiments convincingly supported the quantum predictions. Yet, every experiment requires assumptions that provide loopholes for a local realist explanation. Here, we report a Bell test that closes the most significant of these loopholes simultaneously. Using a well-optimized source of entangled photons, rapid setting generation, and highly efficient superconducting detectors, we observe a violation of a Bell inequality with high statistical significance. The purely statistical probability of our results to occur under local realism does not exceed 3.74 x 10(-31), corresponding to an 11.5 standard deviation effect.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2015
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-123747 (URN)10.1103/PhysRevLett.115.250401 (DOI)000366486600001 ()26722905 (PubMedID)
Note

Funding Agencies|program CoQuS of the FWF (Austrian Science Fund); EU Integrated Project SIQS; European Union Project QUIC [641122]; Spanish MINECO under the Severo Ochoa programme [SEV-2015-0522]; Project MAGO [FIS2011-23520]; Project EPEC [FIS2014-62181-EXP]; Catalan AGAUR SGR Grants [129, 1623]; European Regional Development Fund (FEDER) Grant [TEC2013-46168-R]; Fundacio Privada CELLEX; NIST Quantum Information Science Initiative; Austrian Academy of Sciences (OAW); European Research Council (SIQS) [600645 EU-FP7-ICT]; Austrian Science Fund (FWF) [SFB F40]; European Research Council Project AQUMET

Available from: 2016-01-11 Created: 2016-01-11 Last updated: 2017-11-30
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-1082-8325

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