Kolloquium SoSe 2020

There are at least two socially useful quantum-cryptographic protocols that can only be realized by Einstein-Podolsky-Rosen (EPR) entangled light. Firstly, ‘one-sided device-independent quantum key distribution (QKD)’ with full security against arbitrary attacks on the channel as well on the devices at the receiver site. Secondly, ‘oblivious transfer (OT)’, which is a fundamental building-block that provides security even against malicious parties.
EPR entanglement is of higher quality than generic entanglement because EPR entanglement is the unique resource that allows the prediction of measurement outcomes of any of two non-commuting quantities with an imprecision smaller than the ground state uncertainty. The effect is also known as the EPR paradox. Both protocols were worked out in collaboration with theory groups (Reinhard Werner / Hannover und Stephanie Wehner / Delft.) The proof-of-principle experiments were done in my group. Decoherence on the entangled light limits the protocols to distances of a few kilometres if the light is distributed via commercial glass fibres. There are, however, highly relevant application examples that require just short distances, such as the communication security of government districts and industrial premises.