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Experiments with Entangled Photons: Bell Inequalities, Non-local Games and Bound Entanglement
Stockholm University, Faculty of Science, Department of Physics. (Kvantinformation & Kvantoptik Quantum Information & Quantum Optics)
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Quantum mechanics is undoubtedly a weird field of science, which violates many deep conceptual tenets of classical physics, requiring reconsideration of the concepts on which classical physics is based. For instance, it permits persistent correlations between classically separated systems, that are termed as entanglement. To circumvent these problems and explain entanglement, hidden variables theories--based on undiscovered parameters--have been devised. However, John S. Bell and others invented inequalities that can distinguish between the predictions of local hidden variable (LHV) theories and quantum mechanics. The CHSH-inequality (formulated by J. Clauser, M. Horne, A. Shimony and R. A. Holt), is one of the most famous among these inequalities. In the present work, we found that this inequality actually contains an even simpler logical structure, which can itself be described by an inequality and will be violated by quantum mechanics. We found 3 simpler inequalities and were able to violate them experimentally.

Furthermore, the CHSH inequality can be used to devise games that can outperform classical strategies. We explore CHSH-games for biased and unbiased cases and present their experimental realizations. We also found a remarkable application of CHSH-games in real life, namely in the card game of duplicate Bridge.  In this thesis, we have described this application along with its experimental realization. Moreover, non-local games with quantum inputs can be used to certify entanglement in a measurement device independent manner. We implemented this method and detected entanglement in a set of two-photon Werner states. Our results are in good agreement with theory.

A peculiar form of entanglement that is not distillable through local operations and classical communication (LOCC) is known as bound entanglement (BE). In the present work, we produced and studied BE in four-partite Smolin states and present an experimental violation of a Bell inequality by such states. Moreover we produced a three-qubit BE state, which is also the first experimental realization of a tripartite BE state. We also present its activation, where we experimentally demonstrate super additivity of quantum information resources.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2016. , 89 p.
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-128277ISBN: 978-91-7649-358-8 (print)OAI: oai:DiVA.org:su-128277DiVA: diva2:913824
Public defence
2016-04-28, FP41, AlbaNova universitetscentrum, Roslagstullsbacken 33, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

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

Available from: 2016-04-05 Created: 2016-03-22 Last updated: 2017-02-24Bibliographically approved
List of papers
1. Bell inequalities for the simplest exclusivity graph
Open this publication in new window or tab >>Bell inequalities for the simplest exclusivity graph
2013 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 87, no 1, 012128Article in journal (Refereed) Published
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

National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-88671 (URN)10.1103/PhysRevA.87.012128 (DOI)000314223200002 ()
Funder
Swedish Research Council
Note

AuthorCount:4;

Available from: 2013-03-26 Created: 2013-03-25 Last updated: 2017-12-06Bibliographically approved
2. Quantum Bidding in Bridge
Open this publication in new window or tab >>Quantum Bidding in Bridge
Show others...
2014 (English)In: Physical Review X, ISSN 2160-3308, E-ISSN 2160-3308, Vol. 4, no 2, 021047Article in journal (Refereed) Published
Abstract [en]

Quantum methods allow us to reduce communication complexity of some computational tasks, with several separated partners, beyond classical constraints. Nevertheless, experimental demonstrations of this have thus far been limited to some abstract problems, far away from real-life tasks. We show here, and demonstrate experimentally, that the power of reduction of communication complexity can be harnessed to gain an advantage in a famous, immensely popular, card game-bridge. The essence of a winning strategy in bridge is efficient communication between the partners. The rules of the game allow only a specific form of communication, of very low complexity (effectively, one has strong limitations on the number of exchanged bits). Surprisingly, our quantum technique does not violate the existing rules of the game (as there is no increase in information flow). We show that our quantum bridge auction corresponds to a biased nonlocal Clauser-Horne-Shimony-Holt game, which is equivalent to a 2 -> 1 quantum random access code. Thus, our experiment is also a realization of such protocols. However, this correspondence is not complete, which enables the bridge players to have efficient strategies regardless of the quality of their detectors.

Keyword
Quantum Physics, Quantum Information
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-106595 (URN)10.1103/PhysRevX.4.021047 (DOI)000338666800001 ()
Note

AuthorCount:6;

Available from: 2014-08-13 Created: 2014-08-12 Last updated: 2017-12-05Bibliographically approved
3. Experimental Measurement-Device-Independent Entanglement Detection
Open this publication in new window or tab >>Experimental Measurement-Device-Independent Entanglement Detection
2015 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, 8048Article 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. The determination whether a given state is entangled or not is one of the most challenging open problems of the field. Here we report on the experimental demonstration of measurement-device-independent (MDI) entanglement detection using witness method for general two qubits photon polarization systems. In the MDI settings, there is no requirement to assume perfect implementations or neither to trust the measurement devices. This experimental demonstration can be generalized for the investigation of properties of quantum systems and for the realization of cryptography and communication protocols.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-114346 (URN)10.1038/srep08048 (DOI)000348767200001 ()25649664 (PubMedID)
Note

AuthorCount:4;

Available from: 2015-03-09 Created: 2015-03-02 Last updated: 2017-12-04Bibliographically approved
4. 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
5. Experimental Three-Qubit Bound Entanglement
Open this publication in new window or tab >>Experimental Three-Qubit Bound Entanglement
(English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114Article in journal (Refereed) Submitted
Abstract [en]

Entanglement is one of the most puzzling features of quantum theory and of great importancefor the new eld of quantum information. A peculiar form of entanglement, which emerges inmixed quantum states, is recognized as Bound entanglement since this kind of entanglement is nondistillableby local operations and classical communication. Here we report on the rst experimentaldemonstration of a three qubits bound entangled state and fully characterize its entanglement properties.Remarkably, this is the rst experimental realization of a bound entangled state that can beused for generation of multipartite bound information.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-128273 (URN)
Available from: 2016-03-22 Created: 2016-03-22 Last updated: 2017-11-30Bibliographically approved
6. Superadditivity of two quantum information resources
Open this publication in new window or tab >>Superadditivity of two quantum information resources
(English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114Article in journal (Refereed) Submitted
Abstract [en]

Entanglement is one of the most puzzling features of quantum theory and a principal resource forquantum information processing. It is well known that in classical information theory, the additionof two classical information resources will not lead to any extra advantages. On the contrary, inquantum information a spectacular phenomenon of the super-additivity of two quantum informationresources emerges. It clearly shows that quantum entanglement, which was completely absent inany of the two resources separately, emerges as a result of combining them together. We presentthe rst experimental demonstration of this quantum phenomenon with photonic three-partite nondistillableentangled states.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-128276 (URN)
Available from: 2016-03-22 Created: 2016-03-22 Last updated: 2017-11-30Bibliographically approved

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