Ebook: Quantum Physics: A Text for Graduate Students

The combination of quantum mechanics and quantum ?eld theory cons- tutesthemostrevolutionaryandin?uentialphysicaltheoryofthetwentieth century. Itsimpactisfeltnotonlyinalmostallothersciences,butthefruits of its application are ubiquitous in everyday life. This textbook is designed to teach graduate students the underlying quantum-physical ideas, their mathematical formulations, and the basic problem-solving techniques of the discipline. It assumes they have taken at least one introductory course in quantum mechanics as undergraduates and are familiar with the history of the subject and the basic experimental evidence that led to its adoption, as well as with many of its fundamental notions. In contrast to most other authors, I am therefore not introducing the quantum theory via an hist- ical survey of its early successes. Instead, following the models of books on classsical mechanics or electromagnetism, I develop the theory from its basic assumptions, beginning with statics, followed by the dynamics and details of its speci?c areas of use as well as the needed mathematical te- niques. Although this book, inevitably, deals largely with the behavior of point particles under various conditions, I do not regard particles as the fun- mental entities of the universe: the most basic object is the quantum ?eld, with theobserved particlesarising from the?eld asitsquanta. For thisr- son I introduce quantum ?elds right from the beginning and demonstrate, in the ?rst chapter, how particles originate.

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This text develops quantum theory from its basic assumptions, beginning with statics, followed by dynamics and details of applications and the needed computational techniques. The discussion is based on the view that the fundamental entities of the universe are not particles but fields, with the observed particles arising as their quanta. Quantum fields are thus introduced from the beginning, with a discussion of how they produce quanta that manifest themselves as particles. Most of the book, of course, deals with particle systems, as that is where most of the applications lie; the treatment of quantum field theory is confined to fundamental ideas and their consequences.
For developing quantum dynamics, the author uses the Lagrangian technique with the principle of stationary action. The roots of this approach, which includes generating the canonical commutation rules, go back to a course taught by Julian Schwinger, filtered through many years of the authors own teaching.
The text emphasizes that the wave function does not exist in physical three-dimensional space, but in configuration space, and it points out that the probabilistic features of the theory arise not from a lack of determinism but from the definition of the ''state'' of a system, so that many, though not all, of the counterintuitive aspects of quantum mechanics arise from its probabilistic nature and are shared by other probabilistic theories such as classical statistical mechanics.