Realization of a minimal disturbance quantum measurement

We report the first experimental realization of an ‘‘optimal’’ quantum device able to perform a minimal disturbance measurement on polarization encoded qubits saturating the theoretical boundary established between the classical knowledge acquired of any input state, i.e., a ‘‘classical guess,’’ and the fidelity of the same state after disturbance due to measurement. The device has been physically realized by means of a linear optical qubit manipulation, postselection measurement, and a classical feed-forward process.