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International Journal of Quantum Information: Vol. 09, No. 07n08
Print ISSN: 0219-7499
Online ISSN: 1793-6918

 
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QUANTUM LOCKING OF CLASSICAL CORRELATIONS AND QUANTUM DISCORD OF CLASSICAL-QUANTUM STATES

S. BOIXO

Department of Chemistry and Chemical Biology, Harvard University, Cambridge MA, USA

L. AOLITA

ICFO-Institut de Ciències Fotòniques, Av. Carl Friedrich Gauss 3,08860 Castelldefels (Barcelona), Spain

D. CAVALCANTI

Centre for Quantum Technologies, National University of Singapore, Singapore

K. MODI

Centre for Quantum Technologies, National University of Singapore, Singapore

A. WINTER

Department of Mathematics, University of Bristol, Bristol, UK

Centre for Quantum Technologies, National University of Singapore, Singapore

Received: 15 May 2011

A locking protocol between two parties is as follows: Alice gives an encrypted classical message to Bob which she does not want Bob to be able to read until she gives him the key. If Alice is using classical resources, and she wants to approach unconditional security, then the key and the message must have comparable sizes. But if Alice prepares a quantum state, the size of the key can be comparatively negligible. This effect is called quantum locking. Entanglement does not play a role in this quantum advantage. We show that, in this scenario, the quantum discord quantifies the advantage of the quantum protocol over the corresponding classical one for any classical-quantum state.

Keywords: Quantum discord; entanglement; quantum locking
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