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arXiv · 2111.14129

Infinite dimensionality of the post-processing order of measurements on a general state space

Yui Kuramochi
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Abstract

For a partially ordered set $(S, \mathord\preceq)$, the order (monotone) dimension is the minimum cardinality of total orders (respectively, real-valued order monotone functions) on $S$ that characterize the order $\preceq$. In this paper we consider an arbitrary generalized probabilistic theory and the set of finite-outcome measurements on it, which can be described by effect-valued measures, equipped with the classical post-processing orders. We prove that the order and order monotone dimensions of the post-processing order are (countably) infinite if the state space is not a singleton (and is separable in the norm topology). This result gives a negative answer to the open question for quantum measurements posed in [Guff T \textit{et al.\/} 2021 \textit{J.\ Phys.\ A: Math.\ Theor.} \textbf{54} 225301]. We also consider the quantum post-processing relation of channels with a fixed input quantum system described by a separable Hilbert space $\mathcal{H}$ and show that the order (monotone) dimension is countably infinite when $\dim \mathcal{H} \geq 2$.

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Yui Kuramochi. 2021-11-28. Infinite dimensionality of the post-processing order of measurements on a general state space. https://doi.org/10.1088/1751-8121%2Fac99b0

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