1303.4821 (Erik Woodhead)

A quantum cloning bound and application to quantum key distribution    [PDF]

Erik Woodhead

We introduce a quantum cloning bound which we show can be applied to a straightforward and relatively direct security proof of the prepare-and-measure BB84 protocol against collective attacks. Unlike the vast majority of security analyses, our approach has the attractive feature that we never require the use or manipulation of "virtual" entangled states. We illustrate its versatility by applying it to a BB84 implementation where a non-ideal source emits four given but otherwise arbitrary pure states and where the detector is left largely uncharacterised. The keyrate we derive is an improvement over that predicted by the entropic uncertainty relation in the special case where the states form two orthogonal bases separated by a given angle on the Bloch sphere, and an improvement over a result reported by Mar{\o}y et. al. in the general case. We also provide a stronger result in the more limited scenario of a two-dimensional basis-independent source and two-dimensional detector.

View original: http://arxiv.org/abs/1303.4821