Direct evaluation of measurement uncertainties by feedback compensation of decoherence

It is shown that measurement uncertainties can be observed directly by evaluating the feedback compensation of the decoherence induced by the measured system on a probe qubit in a weak interaction occurring between state preparation and measurement. The uncompensated decoherence is described by the measurement uncertainties introduced by Ozawa in Phys. Rev. A 67, 042105 (2003)PLRAAN1050-294710.1103/PhysRevA.67.042105, confirming the empirical validity of measurement theories that combine the initial information of the input state with the additional information provided by each measurement outcome.