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Direct observation of any two-point quantum correlation function

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arxiv 1312.4240 v1 pith:3EGZ5PVK submitted 2013-12-16 quant-ph cond-mat.stat-mech

classification quant-phcond-mat.stat-mech
keywords correlationtwo-pointquantumdirectfunctionfunctionsobservablesoperational
verification ladder T0 review T1 audit T2 compute T3 formal
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abstract

The existence of noncompatible observables in quantum theory makes a direct operational interpretation of two-point correlation functions problematic. Here we challenge such a view by explicitly constructing a measuring scheme that, independently of the input state $\rho$ and observables $A$ and $B$, performs an unbiased optimal estimation of the two-point correlation function $\operatorname{Tr}[A \ \rho \ B]$. This shows that, also in quantum theory, two-point correlation functions are as operational as any other expectation value. A very simple probabilistic implementation of our proposal is presented.

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Forward citations

Cited by 4 Pith papers

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    hep-th 2026-07 conditional novelty 7.0 of 10

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  2. Virtual Cloning of Quantum States

    quant-ph 2025-07 accept novelty 7.0 of 10

    A set of quantum states can be virtually cloned if and only if their density matrices are linearly independent, and the optimal 1-to-2 cloning cost for any pair of pure states equals sqrt(1+|⟨ψ1|ψ2⟩|²).

  3. Experimental Virtual Quantum Broadcasting

    quant-ph 2025-01 conditional novelty 5.0 of 10

    Researchers experimentally realized virtual quantum broadcasting on an NMR processor by combining a universal cloner with a universal antisymmetrizer via linear combination of unitaries and classical post-processing.

  4. Hermitian Maps: Approximations and Completely Positive Extensions

    math.FA 2025-06 reject novelty 2.0 of 10

    The paper's optimal CP approximation result is a restatement of known matrix projection facts, and its claimed minimal auxiliary dimension (the Choi rank) is false: two dimensions always suffice.

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