  This paper presents two unconventional links between quantum and classical
physics. The first link appears in the study of quantum cryptography. In the
presence of a spy, the quantum correlations shared by Alice and Bob are
imperfect. One can either process the quantum information, recover perfect
correlations and finally measure the quantum systems; or, one can perform the
measurements first and then process the classical information. These two
procedures tolerate exactly the same error rate for a wide class of attacks by
the spy. The m second link is drawn between the quantum notions of "no-cloning
theorem" and "weak-measurements with post-selection", and simple experiments
using classical polarized light and ordinary telecom devices.
