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High-visibility time-bin entanglement for testing chained Bell inequalities
University of Padua, Italy; UOS Padova, Italy.
University of Padua, Italy; UOS Padova, Italy.
Linköping University, Department of Electrical Engineering, Information Coding. Linköping University, Faculty of Science & Engineering.
University of Padua, Italy; UOS Padova, Italy.
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2017 (English)In: Physical Review A, ISSN 2469-9926, Vol. 95, no 3, article id 032107Article in journal (Refereed) Published
Abstract [en]

The violation of Bells inequality requires a well-designed experiment to validate the result. In experiments using energy-time and time-bin entanglement, initially proposed by Franson in 1989, there is an intrinsic loophole due to the high postselection. To obtain a violation in this type of experiment, a chained Bell inequality must be used. However, the local realism bound requires a high visibility in excess of 94.63% in the time-bin entangled state. In this work, we show how such a high visibility can be reached in order to violate a chained Bell inequality with six, eight, and ten terms.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC , 2017. Vol. 95, no 3, article id 032107
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Other Physics Topics
Identifiers
URN: urn:nbn:se:liu:diva-136599DOI: 10.1103/PhysRevA.95.032107ISI: 000395983300003OAI: oai:DiVA.org:liu-136599DiVA, id: diva2:1089969
Available from: 2017-04-21 Created: 2017-04-21 Last updated: 2017-10-20
In thesis
1. Breaking the Unbreakable: Exploiting Loopholes in Bell’s Theorem to Hack Quantum Cryptography
Open this publication in new window or tab >>Breaking the Unbreakable: Exploiting Loopholes in Bell’s Theorem to Hack Quantum Cryptography
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis we study device-independent quantum key distribution based on energy-time entanglement. This is a method for cryptography that promises not only perfect secrecy, but also to be a practical method for quantum key distribution thanks to the reduced complexity when compared to other quantum key distribution protocols. However, there still exist a number of loopholes that must be understood and eliminated in order to rule out eavesdroppers. We study several relevant loopholes and show how they can be used to break the security of energy-time entangled systems. Attack strategies are reviewed as well as their countermeasures, and we show how full security can be re-established.

Quantum key distribution is in part based on the profound no-cloning theorem, which prevents physical states to be copied at a microscopic level. This important property of quantum mechanics can be seen as Nature's own copy-protection, and can also be used to create a currency based on quantummechanics, i.e., quantum money. Here, the traditional copy-protection mechanisms of traditional coins and banknotes can be abandoned in favor of the laws of quantum physics. Previously, quantum money assumes a traditional hierarchy where a central, trusted bank controls the economy. We show how quantum money together with a blockchain allows for Quantum Bitcoin, a novel hybrid currency that promises fast transactions, extensive scalability, and full anonymity.

Abstract [sv]

En viktig konsekvens av kvantmekaniken är att okända kvanttillstånd inte kan klonas. Denna insikt har gett upphov till kvantkryptering, en metod för två parter att med perfekt säkerhet kommunicera hemligheter. Ett komplett bevis för denna säkerhet har dock låtit vänta på sig eftersom en attackerare i hemlighet kan manipulera utrustningen så att den läcker information. Som ett svar på detta utvecklades apparatsoberoende kvantkryptering som i teorin är immun mot sådana attacker.

Apparatsoberoende kvantkryptering har en mycket högre grad av säkerhet än vanlig kvantkryptering, men det finns fortfarande ett par luckor som en attackerare kan utnyttja. Dessa kryphål har tidigare inte tagits på allvar, men denna avhandling visar hur även små svagheter i säkerhetsmodellen läcker information till en attackerare. Vi demonstrerar en praktisk attack där attackeraren aldrig upptäcks trots att denne helt kontrollerar systemet. Vi visar också hur kryphålen kan förhindras med starkare säkerhetsbevis.

En annan tillämpning av kvantmekanikens förbud mot kloning är pengar som använder detta naturens egna kopieringsskydd. Dessa kvantpengar har helt andra egenskaper än vanliga mynt, sedlar eller digitala banköverföringar. Vi visar hur man kan kombinera kvantpengar med en blockkedja, och man får då man en slags "kvant-Bitcoin". Detta nya betalningsmedel har fördelar över alla andra betalsystem, men nackdelen är att det krävs en kvantdator.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017. p. 239
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1875
National Category
Atom and Molecular Physics and Optics Communication Systems
Identifiers
urn:nbn:se:liu:diva-140912 (URN)10.3384/diss.diva-140912 (DOI)9789176854600 (ISBN)
Public defence
2017-11-17, Ada Lovelace, B House, Campus Valla, Linköping, 13:00 (English)
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Available from: 2017-10-23 Created: 2017-10-20 Last updated: 2017-10-23Bibliographically approved

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