The Algebra of Microscopic Measurement

Masanao Ozawa

In the algebraic approach to the quantum physics, the notion of a macroscopic observable has been well established. This paper examines a program for the unification of classical mechanics and quantum mechanics based on the macroscopic observable and the algebraic description of a dynamical system such as a C*-dynamical system. It is proved quite generally that in this approach we cannot describe the measuring interaction between a microscopic system and a macroscopic apparatus by a C*-dynamical system, or any similar frameworks, as long as the time reversibility of the dynamics of isolated systems is assumed.

Masanao Ozawa

In the algebraic approach to the quantum physics, the notion of a macroscopic observable has been well established. This paper examines a program for the unification of classical mechanics and quantum mechanics based on the macroscopic observable and the algebraic description of a dynamical system such as a C*-dynamical system. It is proved quite generally that in this approach we cannot describe the measuring interaction between a microscopic system and a macroscopic apparatus by a C*-dynamical system, or any similar frameworks, as long as the time reversibility of the dynamics of isolated systems is assumed.

N. G. van Kampen

Włodzimierz M. Tulczyjew

It is widely believed that statistical interpretation of quantum mechanics requires that density operators representing quantum states be normalized. We present a description of selective measurements in terms of density operators. The description is inspired by Schwinger's Algebra of Microscopic Measurements. Density operators used are not normalized. We do not know applications of density operators requiring normalization.

Song He

A variational principle for quantum-state distinguishability is established in many-body systems with generalized symmetries, including noninvertible cases described by fusion categories. Standard fidelity and symmetry-resolved diagnostics emerge as coarse-grained limits of a more refined operational structure. When symmetry actions terminate at entanglement cuts, distinguishability is governed by boundary tube algebras within a symmetry-constrained measurement resource theory. The physically admissible instruments are characterized by complete positivity, entanglement-cut locality, boundary-module covariance, and sequential stability. The resulting optimal measurement structure is uniquely fixed by the center of the boundary tube algebra, $\mathcal{A}_{\mathrm{phys}} = Z\!\left(\mathrm{Tube}_{\mathcal{C}}(\mathcal{M}_A)\right)$, whose primitive dempotents define tube-sector probabilities that refine fidelity-based and symmetry-resolved descriptions. The associated tube positive-operator-valued measures (POVMs) are extremal and yield optimal one-shot hypothesis-testing distinguishability under symmetry constraints. The categorical selection rule is universal across fusion categories and independent of microscopic realization; microscopic models enter by choosing the boundary module and the protocol family used to witness a nontrivial tube fiber.