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Experimental filtering of two-, four-, and six-photon singlets from a single parametric down-conversion source
Stockholm University, Faculty of Science, Department of Physics.
Institute for Theoretical Physics and Astrophysics, Uniwersytet Gdański.
Institute for Theoretical Physics and Astrophysics, Uniwersytet Gdański.
Stockholm University, Faculty of Science, Department of Physics.
2009 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 80, no 040302Article in journal (Refereed) Published
Abstract [en]

Invariant entangled states remain unchanged under simultaneous identical unitary transformations of all their subsystems. We experimentally generate and characterize such invariant two-, four-, and six-photon polarization entangled states. This is done only with a suitable filtering procedure of multiple emissions of entangled photon pairs from a single source without any interferometric overlaps. We get the desired states utilizing bosonic emission enhancement due to indistinguishability. The setup is very stable and gives high interference contrasts. Thus, the process is a very likely candidate for various photonic demonstrations of quantum information protocols.

Place, publisher, year, edition, pages
2009. Vol. 80, no 040302
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-33049DOI: 10.1103/PhysRevA.80.040302ISI: 000271351000006OAI: oai:DiVA.org:su-33049DiVA: diva2:282274
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

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