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Entangled state quantum cryptography: Eavesdropping on the Ekert protocol

D. S. Naik, C. G. Peterson, A. G. White, A. J. Berglund, P. G. Kwiat

quant-pharXiv:quant-ph/9912105

Abstract

Using polarization-entangled photons from spontaneous parametric downconversion, we have implemented Ekert's quantum cryptography protocol. The near-perfect correlations of the photons allow the sharing of a secret key between two parties. The presence of an eavesdropper is continually checked by measuring Bell's inequalities. We investigated several possible eavesdropper strategies, including pseudo-quantum non-demolition measurements. In all cases, the eavesdropper's presence was readily apparent. We discuss a procedure to increase her detectability.

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