Combinations of Quantum Observables and Instruments

• URL: http://arxiv.org/abs/2010.08025v1
• Date: Thu, 15 Oct 2020 21:26:22 GMT
• Title: Combinations of Quantum Observables and Instruments
• Authors: Stan Gudder
• Abstract summary: We study parts of observables, post-processing, generalized convex combinations, sequential products and tensor products. We consider properties of observables measured by combinations of instruments. In this work, we only consider finite-dimensional quantum systems.
• Score: 0.0
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: This article points out that observables and instruments can be combined in many ways that have natural and physical interpretations. We shall mainly concentrate on the mathematical properties of these combinations. Section~1 reviews the basic definitions and observables are considered in Section~2. We study parts of observables, post-processing, generalized convex combinations, sequential products and tensor products. These combinations are extended to instruments in Section~3. We consider properties of observables measured by combinations of instruments. We introduce four special types of instruments, namely Kraus, L\"uders, trivial and semitrivial instruments. We study when these types are closed under various combinations. In this work, we only consider finite-dimensional quantum systems. A few of the results presented here have appeared in the author's previous articles.

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