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Fundamental mathematical Structures of Quantum Theory

by Valter Moretti

23 luglio 2019
Versione stampabile

This textbook presents in a concise and self-contained way the advanced fundamental mathematical structures in quantum theory. It is based on lectures prepared for a 6 months course for MSc students. The reader is introduced to the beautiful interconnection between logic, lattice theory, general probability theory, and general spectral theory including the basic theory of von Neumann algebras and of the algebraic formulation, naturally arising in the study of the mathematical machinery of quantum theories. Some general results concerning hidden-variable interpretations of QM such as Gleason's and  the Kochen-Specker theorems and the related notions of realism and non-contextuality are carefully discussed. This is done also in relation  with the famous Bell (BCHSH) inequality concerning local causality.

Written in a didactic style, this book includes many examples and solved exercises.

The work is organized as follows. Chapter 1 reviews some elementary facts and properties of quantum systems. Chapter 2 and 3 present the main results of spectral analysis in complex Hilbert spaces. Chapter 4 introduces the point of view of the orthomodular lattices' theory. Quantum theory form this perspective turns out to the probability measure theory on the non-Boolean lattice of elementary observables and Gleason's theorem characterizes all these measures. Chapter 5 deals with some philosophical and interpretative aspects of quantum theory like hidden-variable formulations of QM. The Kochen-Specker theorem and its implications are analyzed also in relation BCHSH inequality, entanglement, realism, locality, and non-contextuality. Chapter 6 focuses on the algebra of observables also in the presence of superselection rules introducing the notion of von Neumann algebra. Chapter 7 offers the idea of (groups of) quantum symmetry, in particular, illustrated in terms of Wigner and Kadison theorems. Chapter 8 deals with the elementary ideas and results of the so called algebraic formulation of quantum theories in terms of both *-algebras and C*-algebras.

This book should appeal to a dual readership: on one hand mathematicians that wish to acquire the tools that unlock the physical aspects of quantum theories; on the other physicists eager to solidify their understanding of the mathematical scaffolding of quantum theories.

Valter Moretti is full professor at the University of Trento, Department of Mathematics

From Chapter 7.1 Quantum Symmetries According to Kadison and Wigner (pag.253-254)

Generally speaking, symmetries are supposed to describe mathematically certain concrete transformations acting either on the physical system or on the instruments used to analyze the system. From a very general standing a symmetry is an active transformation of either the quantum system or, by duality, the observables representing physical instruments. It is further required that

 (1) the transformation is bijective, in the sense that

(a) every state of the system or observable representing devices (according to the notion employed) can be reached by transforming the initial state or observable;

(b) every symmetry admits an inverse;

(2) the transformation should preserve some mathematical structure of the space of the states or the space of observables. This is what distinguishes between the various notions of symmetry.

Alas, there exists in the literature an intrinsically different notion of gauge symmetry. A gauge symmetry is not a symmetry in the above sense. A symmetry acts on the physical system by explicitly changing its state or the (observables representing the) instruments, whereas a gauge symmetry is a mathematical transformation that does not change anything that is directly related to measurements, hence it does not affect the system’s states nor the instruments. An example for a system with algebra of observables  ℜ is the action of elements U of commutant group  (the group of unitary operators in ℜ’ ) on quantum probability measures on L  ℜ (H) describing the states of a quantum system, see Sect. 6.3.2. Quantum states associated to two measures ρ and ρ(U · U ˉ¹) cannot be distinguished by acting on L  ℜ (H) because U P U ˉ¹=  P for every P ∈ L  ℜ (H) as we observed in Sect. 6.3.4 from a slightly different perspective.


Courtesy by Springer