  Information-theoretic uncertainty relations formulate the joint
immeasurability of two non-commuting observables in terms of information
entropies. The trade-off of the accuracy in the outcome of two successive
measurements manifests in entropic noise-disturbance uncertainty relations.
Recent theoretical analysis predicts that projective measurements are not
optimal, with respect to the noise-disturbance trade-offs. Therefore the
results in our previous letter [PRL 115, 030401 (2015)] are outperformed by
general quantum measurements. Here, we experimentally test a tight
information-theoretic measurement uncertainty relation for three-outcome
positive-operator valued measures (POVM), using neutron spin-1/2 qubits. The
obtained results violate the lower bound for projective measurements as
theoretically predicted.
