title: Experimental Test of Residual Error-Disturbance Uncertainty Relations for Mixed Spin-½ States.
abstract: The indeterminacy inherent in quantum measurements is an outstanding character of quantum theory, which manifests itself typically in the uncertainty principle. In the last decade, several universally valid forms of error-disturbance uncertainty relations were derived for completely general quantum measurements for arbitrary states. Subsequently, Branciard established a form that is optimal for spin measurements for some pure states. However, the bound in his inequality is not stringent for mixed states. One of the present authors recently derived a new bound tight in the corresponding mixed state case. Here, a neutron-optical experiment is carried out to investigate this new relation: it is tested whether error and disturbance of quantum measurements disappear or persist in mixing up the measured ensemble. The attainability of the new bound is experimentally observed, falsifying the tightness of Branciard's bound for mixed spin states.
authors.affiliation: Atominstitut, TU Wien, Stadionallee 2, 1020 Vienna, Austria.
authors.forename: Bülent
authors.initials: B
authors.lastname: Demirel
authors.affiliation: Atominstitut, TU Wien, Stadionallee 2, 1020 Vienna, Austria.
authors.forename: Stephan
authors.initials: S
authors.lastname: Sponar
authors.affiliation: Atominstitut, TU Wien, Stadionallee 2, 1020 Vienna, Austria.
authors.forename: Georg
authors.initials: G
authors.lastname: Sulyok
authors.affiliation: Graduate School of Information Science, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan.
authors.forename: Masanao
authors.initials: M
authors.lastname: Ozawa
authors.affiliation: Atominstitut, TU Wien, Stadionallee 2, 1020 Vienna, Austria.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Hasegawa