Witnessing causal nonseparability
Our common understanding of the physical world deeply relies on the notion that events are ordered with respect to some time parameter, with past events serving as causes for future ones. Nonetheless, it was recently found that it is possible to formulate quantum mechanics without any reference to a...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2015-01-01
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| Series: | New Journal of Physics |
| Subjects: | |
| Online Access: | https://doi.org/10.1088/1367-2630/17/10/102001 |
| _version_ | 1797751074755444736 |
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| author | Mateus Araújo Cyril Branciard Fabio Costa Adrien Feix Christina Giarmatzi Časlav Brukner |
| author_facet | Mateus Araújo Cyril Branciard Fabio Costa Adrien Feix Christina Giarmatzi Časlav Brukner |
| author_sort | Mateus Araújo |
| collection | DOAJ |
| description | Our common understanding of the physical world deeply relies on the notion that events are ordered with respect to some time parameter, with past events serving as causes for future ones. Nonetheless, it was recently found that it is possible to formulate quantum mechanics without any reference to a global time or causal structure. The resulting framework includes new kinds of quantum resources that allow performing tasks—in particular, the violation of causal inequalities —which are impossible for events ordered according to a global causal order. However, no physical implementation of such resources is known. Here we show that a recently demonstrated resource for quantum computation—the quantum switch —is a genuine example of ‘indefinite causal order’. We do this by introducing a new tool—the causal witness —which can detect the causal nonseparability of any quantum resource that is incompatible with a definite causal order. We show however that the quantum switch does not violate any causal inequality. |
| first_indexed | 2024-03-12T16:43:09Z |
| format | Article |
| id | doaj.art-0da504adc80946d2849c66802a6368cc |
| institution | Directory Open Access Journal |
| issn | 1367-2630 |
| language | English |
| last_indexed | 2024-03-12T16:43:09Z |
| publishDate | 2015-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | New Journal of Physics |
| spelling | doaj.art-0da504adc80946d2849c66802a6368cc2023-08-08T14:21:14ZengIOP PublishingNew Journal of Physics1367-26302015-01-01171010200110.1088/1367-2630/17/10/102001Witnessing causal nonseparabilityMateus Araújo0Cyril Branciard1Fabio Costa2Adrien Feix3Christina Giarmatzi4Časlav Brukner5Faculty of Physics, University of Vienna , Boltzmanngasse 5, A-1090 Vienna, Austria; Institute for Quantum Optics and Quantum Information (IQOQI) , Boltzmanngasse 3, A-1090 Vienna, AustriaInstitut Néel, CNRS and Université Grenoble Alpes , F-38042 Grenoble Cedex 9, FranceFaculty of Physics, University of Vienna , Boltzmanngasse 5, A-1090 Vienna, Austria; Institute for Quantum Optics and Quantum Information (IQOQI) , Boltzmanngasse 3, A-1090 Vienna, Austria; Centre for Engineered Quantum Systems, School of Mathematics and Physics, The University of Queensland , St Lucia, QLD 4072, AustraliaFaculty of Physics, University of Vienna , Boltzmanngasse 5, A-1090 Vienna, Austria; Institute for Quantum Optics and Quantum Information (IQOQI) , Boltzmanngasse 3, A-1090 Vienna, AustriaCentre for Engineered Quantum Systems, School of Mathematics and Physics, The University of Queensland , St Lucia, QLD 4072, Australia; Centre for Quantum Computer and Communication Technology, School of Mathematics and Physics, University of Queensland , Brisbane, QLD 4072, AustraliaFaculty of Physics, University of Vienna , Boltzmanngasse 5, A-1090 Vienna, Austria; Institute for Quantum Optics and Quantum Information (IQOQI) , Boltzmanngasse 3, A-1090 Vienna, AustriaOur common understanding of the physical world deeply relies on the notion that events are ordered with respect to some time parameter, with past events serving as causes for future ones. Nonetheless, it was recently found that it is possible to formulate quantum mechanics without any reference to a global time or causal structure. The resulting framework includes new kinds of quantum resources that allow performing tasks—in particular, the violation of causal inequalities —which are impossible for events ordered according to a global causal order. However, no physical implementation of such resources is known. Here we show that a recently demonstrated resource for quantum computation—the quantum switch —is a genuine example of ‘indefinite causal order’. We do this by introducing a new tool—the causal witness —which can detect the causal nonseparability of any quantum resource that is incompatible with a definite causal order. We show however that the quantum switch does not violate any causal inequality.https://doi.org/10.1088/1367-2630/17/10/102001quantum informationcausalityquantum foundations |
| spellingShingle | Mateus Araújo Cyril Branciard Fabio Costa Adrien Feix Christina Giarmatzi Časlav Brukner Witnessing causal nonseparability New Journal of Physics quantum information causality quantum foundations |
| title | Witnessing causal nonseparability |
| title_full | Witnessing causal nonseparability |
| title_fullStr | Witnessing causal nonseparability |
| title_full_unstemmed | Witnessing causal nonseparability |
| title_short | Witnessing causal nonseparability |
| title_sort | witnessing causal nonseparability |
| topic | quantum information causality quantum foundations |
| url | https://doi.org/10.1088/1367-2630/17/10/102001 |
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