  In the distribution of quantum states over a long distance, not only are
quantum states corrupted by interactions with an environment but also a
measurement setting should be re-aligned such that detection events can be
ensured for the resulting states. In this work, we present
measurement-protected quantum key distribution where a measurement is protected
against the interactions quantum states experience during the transmission,
without the verification of a channel. As a result, a receiver does not have to
revise the measurement that has been prepared in a noiseless scenario since it
would remain ever optimal. The measurement protection is achieved by
applications of local unitary transformations before and after the
transmission, that leads to a supermap transforming an arbitrary channel to a
depolarization one. An experimental demonstration is presented with the
polarization encoding on photonic qubits. It is shown that the security bounds
for prepare-and-measure protocols can be improved, for instance, errors up to
20.7% can be tolerated in the Bennett-Brassard 1984 protocol.
