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State-Independent Quantum Contextuality with Single Photons
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
Stockholm University, Faculty of Science, Department of Physics.
Departamento de Física Aplicada II, Universidad de Sevilla.
2009 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 160405Article in journal (Refereed) Published
Abstract [en]

Wepresent an experimental state-independent violation of an inequality for noncontextualtheories on single particles. We show that 20 different single-photonstates violate an inequality which involves correlations between results ofsequential compatible measurements by at least 419 standard deviations. Ourresults show that, for any physical system, even for asingle system, and independent of its state, there is auniversal set of tests whose results do not admit anoncontextual interpretation. This sheds new light on the role ofquantum mechanics in quantum information processing.

Place, publisher, year, edition, pages
2009. Vol. 103, no 160405
National Category
Natural Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-33052DOI: 10.1103/PhysRevLett.103.160405ISI: 000270899500005OAI: oai:DiVA.org:su-33052DiVA: diva2:282277
Available from: 2009-12-18 Created: 2009-12-18 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Photonic quantum information and experimental tests of foundations of quantum mechanics
Open this publication in new window or tab >>Photonic quantum information and experimental tests of foundations of quantum mechanics
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Entanglement is a key resource in many quantum information schemes and in the last years the research on multi-qubit entanglement has drawn lots of attention. In this thesis the experimental generation and characterisation of multi-qubit entanglement is presented. Specifically we have prepared entangled states of up to six qubits. The qubits were implemented in the polarisation degree of freedom of single photons. We emphasise that one type of states that we produce are rotationally invariant states, remaining unchanged under simultaneous identical unitary transformations of all their individual constituents. Such states can be applied to e.g. decoherence-free encoding, quantum communication without sharing a common reference frame, quantum telecloning, secret sharing and remote state preparation schemes. They also have properties which are interesting in studies of foundations of quantum mechanics.

In the experimental implementation we use a single source of entangled photon pairs, based on parametric down-conversion, and extract the first, second and third order events. Our experimental setup is completely free from interferometric overlaps, making it robust and contributing to a high fidelity of the generated states. To our knowledge, the achieved fidelity is the highest that has been observed for six-qubit entangled states and our measurement results are in very good agreement with predictions of quantum theory.

We have also performed another novel test of the foundations of quantum mechanics. It is based on an inequality that is fulfilled by any non-contextual hidden variable theory, but can be violated by quantum mechanics. This test is similar to Bell inequality tests, which rule out local hidden variable theories as possible completions of quantum mechanics. Here, however, we show that non-contextual hidden variable theories cannot explain certain experimental results, which are consistent with quantum mechanics. Hence, neither of these theories can be used to make quantum mechanics complete.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2010. 117 p.
Keyword
Quantum information, quantum optics, foundations of quantum mechanics, entanglement, non-contextuality, Kochen-Specker theorem, parametric down-conversion, quantum state engineering
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-37464 (URN)978-91-7447-028-4 (ISBN)
Public defence
2010-04-15, sal FB42, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2010-03-24 Created: 2010-03-05 Last updated: 2010-03-29Bibliographically approved
2. Dynamics of Quantum Correlations with Photons: Experiments on bound entanglement and contextuality for application in quantum information
Open this publication in new window or tab >>Dynamics of Quantum Correlations with Photons: Experiments on bound entanglement and contextuality for application in quantum information
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The rapidly developing interdisciplinary field of quantum information, which merges quantum and information science, studies non-classical aspects of quantum systems. These studies are motivated by the promise that the non-classicality can be used to solve tasks more efficiently than classical methods would allow. In many quantum informational studies, non-classical behaviour is attributed to the notion of entanglement.

In this thesis we use photons to experimentally investigate fundamental questions such as: What happens to the entanglement in a system when it is affected by noise? In our study of noisy entanglement we pursue the challenging task of creating bound entanglement. Bound entangled states are created through an irreversible process that requires entanglement. Once in the bound regime, entanglement cannot be distilled out through local operations assisted by classical communication. We show that it is possible to experimentally produce four-photon bound entangled states and that a violation of a Bell inequality can be achieved. Moreover, we demonstrate an entanglement-unlocking protocol by relaxing the condition of local operations.

We also explore the non-classical nature of quantum mechanics in several single-photon experiments. In these experiments, we show the violation of various inequalities that were derived under the assumption of non-contextuality. Using qutrits we construct and demonstrate the simplest possible test that offers a discrepancy between classical and quantum theory. Furthermore, we perform an experiment in the spirit of the Kochen-Specker theorem to illustrate the state-independence of this theorem. Here, we investigate whether or not measurement outcomes exhibit fully contextual correlations. That is, no part of the correlations can be attributed to the non-contextual theory. Our results show that only a small part of the experimental generated correlations are amenable to a non-contextual interpretation.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2012. 102 p.
Keyword
Quantum information, quantum optics, foundations of quantum mechanics, entanglement, non-contextuality, Kochen-Specker theorem, parametric down-conversion, quantum state engineering
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-66469 (URN)978-91-7447-421-3 (ISBN)
Public defence
2012-01-26, FA31, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 5: Submitted. Paper 6: Submitted.

Available from: 2012-01-04 Created: 2011-12-20 Last updated: 2015-04-30Bibliographically approved

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