Konrad Banaszek, University of Warsaw
Abstract
According to the recently developed theory of quantum privacy, the
extraction of a secure cryptographic key from certain noisy bipartite
quantum states can be carried out much more efficiently compared to the
approach based on standard entanglement distillation protocols. It is
even possible to generate the key using so-called bound-entangled states
from which no pure entanglement can be distilled. In this presentation,
we will give an elementary introduction to the theory of quantum privacy
and present experimental generation and verification of noisy entangled
four-photon states that exhibit separation between the secure key
contents and distillable entanglement. The privacy analysis, based on
the full tomographic reconstruction of the prepared states, reveals
non-trivial statistical aspects of characterising the usefulness of
photonic states for quantum information protocols. We also describe
strategies to infer the privacy of the states from few-observable
measurements