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Finding a state in a haystack

Niko Donath·Karl Svozil
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Abstract

We consider the problem to single out a particular state among $2^n$ orthogonal pure states. As it turns out, in general the optimal strategy is not to measure the particles separately, but to consider joint properties of the $n$-particle system. The required number of propositions is $n$. There exist $2^n!$ equivalent operational procedures to do so. We enumerate some configurations for three particles, in particular the Greenberger-Horne-Zeilinger (GHZ)- and W-states, which are specific cases of a unitary transformation For the GHZ-case, an explicit physical meaning of the projection operators is discussed.

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Niko Donath, Karl Svozil. 2001-05-11. Finding a state in a haystack. https://doi.org/10.1103/physreva.65.044302

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