145 research outputs found
Experimental test of an entropic measurement uncertainty relation for arbitrary qubit observables
A tight information-theoretic measurement uncertainty relation is
experimentally tested with neutron spin-1/2 qubits. The noise associated to the
measurement of an observable is defined via conditional Shannon entropies and a
tradeoff relation between the noises for two arbitrary spin observables is
demonstrated. The optimal bound of this tradeoff is experimentally obtained for
various non-commuting spin observables. For some of these observables this
lower bound can be reached with projective measurements, but we observe that,
in other cases, the tradeoff is only saturated by general quantum measurements
(i.e., positive-operator valued measures), as predicted theoretically.Comment: 6 pages, 3 figure
Kochen-Specker theorem studied with neutron interferometer
The Kochen-Specker theorem theoretically shows evidence of the
incompatibility of noncontextual hidden variable theories with quantum
mechanics. Quantum contextuality is a more general concept than quantum
non-locality which is quite well tested in experiments by using Bell
inequalities. Within neutron interferometry we performed an experimental test
of the Kochen-Specker theorem with an inequality, which identifies quantum
contextuality, by using spin-path entanglement in a single neutron system. Here
entanglement is achieved not between different particles, but between degrees
of freedom, i.e., between spin and path degree of freedom. Appropriate
combinations of the spin analysis and the position of the phase shifter allow
an experimental verification of the violation of an inequality of the
Kochen-Specker theorem. The observed value of (2.291 +/- 0.008), which is above
the threshold of 1, clearly shows that quantum mechanical predictions cannot be
reproduced by noncontextual hidden variable theories.Comment: 5 pages, 3 figure
Energy entanglement in neutron interferometry
Entanglement between degrees of freedom, namely between the spin, path and
(total) energy degrees of freedom, for single neutrons is exploited. We
implemented a triply entangled Greenberger-Horne-Zeilinger(GHZ)-like state and
coherently manipulated relative phases of two-level quantum subsystems. An
inequality derived by Mermin was applied to analyze the generated GHZ-like
state: we determined the four expectation values and finally obtained M=2.558
+/- 0.004 which is clearly above the threshold of 2. This demonstrates the
violation of a Mermin-like inequality for triply entangled GHZ-like state in a
single-particle system, which, in turn, exhibits a clear inconsistency between
noncontextual assumptions and quantum mechanics and confirms quantum
contextuality.Comment: 4 pages, 3 figure
Violation of Bell-like Inequality for spin-energy entanglement in neutron polarimetry
Violation of a Bell-like inequality for a spin-energy entangled neutron state
has been confirmed in a polarimetric experiment. The proposed inequality, in
Clauser-Horne-Shimony-Holt (CHSH) formalism, relies on correlations between the
spin and energy degree of freedom in a single-neutron system. The entangled
states are generated utilizing a suitable combination of two radio-frequency
fields in a neutron polarimeter setup. The correlation function S is determined
to be 2.333+/-0.005, which violates the Bell-like CHSH inequality by more than
66 standard deviations.Comment: 4 pages 2 figure
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