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Dynamics of Quantum Correlations with Photons: Experiments on bound entanglement and contextuality for application in quantum information
Stockholm University, Faculty of Science, Department of Physics. (Kondenserad materia och kvantoptik)
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 [en]
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: urn:nbn:se:su:diva-66469ISBN: 978-91-7447-421-3 (print)OAI: oai:DiVA.org:su-66469DiVA: diva2:468021
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
List of papers
1. Experimental four-qubit bound entanglement
Open this publication in new window or tab >>Experimental four-qubit bound entanglement
2009 (English)In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 5, no 10, 748-752 p.Article in journal (Refereed) Published
Abstract [en]

Entanglement is one of the most puzzling features of quantum theory and of great importance for the new field of quantum information. Being a peculiar form of entanglement, bound entanglement emerges in certain mixed quantum states. This form of entanglement is not distillable by local operators and classical communication. Bound-entangled states are different from both the free entangled (distillable) and separable states. Here we report on the first experimental demonstration of a four-qubit polarization bound-entangled state, the so-called Smolin state. We have fully characterized its entanglement properties. Moreover, we have realized unlocking of the entanglement protocol for this state. The special properties of the Smolin state constitute a useful quantum resource for new multiparty communication schemes.

Keyword
mixed states, separability criterion, density-matrices, quantum
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-59659 (URN)10.1038/NPHYS1372 (DOI)000271185400016 ()
Note
authorCount :2Available from: 2011-08-01 Created: 2011-07-05 Last updated: 2017-12-08Bibliographically approved
2. Reply to 'Experimental bound entanglement?'
Open this publication in new window or tab >>Reply to 'Experimental bound entanglement?'
2010 (English)In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 6, 827-827 p.Article in journal (Other (popular science, discussion, etc.)) Published
Place, publisher, year, edition, pages
Macmillan Publishers Ltd., 2010
Keyword
quantum physics entanglement photon
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-66449 (URN)10.1038/nphys1833 (DOI)
Note
correspondence about experimental bound entanglement. Available from: 2011-12-20 Created: 2011-12-20 Last updated: 2017-12-08Bibliographically approved
3. Experimental bound entanglement through a Pauli channel
Open this publication in new window or tab >>Experimental bound entanglement through a Pauli channel
2013 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, 1966Article in journal (Refereed) Published
Abstract [en]

Understanding the characteristics of a quantum systems when affected by noise is one of the biggest challenges for quantum technologies. The general Pauli error channel is an important lossless channel for quantum communication. In this work we consider the effects of a Pauli channel on a pure four-qubit state and simulate the Pauli channel experimentally by studying the action on polarization encoded entangled photons. When the noise channel acting on the photons is correlated, a set spanned by four orthogonal bound entangled states can be generated. We study this interesting case experimentally and demonstrate that products of Bell states can be brought into a bound entangled regime. We find states in the set of bound entangled states which experimentally violate the CHSH inequality while still possessing a positive partial transpose.

National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-66457 (URN)10.1038/srep01966 (DOI)000320130300005 ()
Available from: 2011-12-20 Created: 2011-12-20 Last updated: 2017-12-08Bibliographically approved
4. State-Independent Quantum Contextuality with Single Photons
Open this publication in new window or tab >>State-Independent Quantum Contextuality with Single Photons
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.

National Category
Natural Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-33052 (URN)10.1103/PhysRevLett.103.160405 (DOI)000270899500005 ()
Available from: 2009-12-18 Created: 2009-12-18 Last updated: 2017-12-12Bibliographically approved
5. Two Fundamental Experimental Tests of Nonclassicality with Qutrits
Open this publication in new window or tab >>Two Fundamental Experimental Tests of Nonclassicality with Qutrits
2013 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, 2170Article in journal (Refereed) Published
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.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-92626 (URN)10.1038/srep02170 (DOI)000321548300001 ()
Note

AuthorCount:4;

Available from: 2013-08-19 Created: 2013-08-14 Last updated: 2017-12-06Bibliographically approved
6. Experimental fully contextual correlations
Open this publication in new window or tab >>Experimental fully contextual correlations
Show others...
(English)Article in journal (Refereed) Submitted
Abstract [en]

Quantum correlations are contextual yet, in general, nothing prevents the existence of even morecontextual correlations. We identify and test a simple noncontextual inequality in which the quantumviolation cannot be improved by any hypothetical post-quantum resource, and use it to experimentally obtain correlations in which the maximum noncontextual content, defined as the maximumfraction of noncontextual correlations, is less than 0.06. Our correlations are experimentally generated from the outcomes of sequential compatible measurements on a four-state quantum system encoded in the polarization and path of a single photon.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:su:diva-66460 (URN)
Available from: 2011-12-20 Created: 2011-12-20 Last updated: 2011-12-20Bibliographically approved

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