Entanglement

October 25, 2016 Published by

Entanglement

occupies a peculiar position in quantum theory. It occurs in quantum systems that consist of space-like separated parts or—more generally—in systems whose observables belong to disjoint Hilbert spaces. The latter is the case for instance for spin, path and energy degree of freedom in the single-neutron systems in terms of or bipartite and tripartite entanglement. Apart from Bell’s theorem, there exists a second powerful argument against the possibility of extending QM into a more complete theory, namely the Kochen–Specker (KS) theorem. The KS theorem sets certain constraints on classes of hidden variable theories, which try to explain the apparent randomness of quantum mechanics as a deterministic model featuring hidden states.

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Bell’s Inequality Experiments

September 22, 2016 Published by

The remarkable discovery made by John S. Bell, namely that quantum mechanics cannot be counterfactual (definiteness of results prior to measurement) and local (physical objects are only influenced by its immediate surroundings) gave rise to a number of experiments probing the foundations quantum mechanics. We prepare our neutrons in a spin-path entangled state and measure correlations that arise between observables of otherwise independent degrees of freedom in the single neutron system in order to validate the presence of entanglement.

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Greenberger–Horne–Zeilinger & W State Preparation

September 21, 2016 Published by

Greenberger–Horne–Zeilinger (GHZ) and W states represent two very different kinds of tripartite entanglement. We prepare entanglement between the spin, path, and (total) energy degrees of freedom, in a single-neutron system. We implemented a triply entangled GHZ–like states, as well as W states, and coherently manipulated relative phases of two-level quantum subsystems.

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Experimental Tests of the Kochen-Specker Theorem

October 20, 2015 Published by

The Kochen-Specker (KS) Theorem sets constrains on hidden-variable theories which try to explain the randomness of quantum mechanics in terms of a as a deterministic theory. We perform experimental tests of the Kochen-Specker theorem based on an inequality derived from the Peres-Mermin proof, using spin-path (momentum) entanglement in a single neutron system. A Bell-like state was generated, and three expectation values were determined. The observed violation clearly shows that quantum mechanical predictions cannot be reproduced by noncontextual hidden- variable theories.