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This book is intended as a text for a core graduate course on quantum physics. The modern form of quantum mechanics emerged in a remarkable burst of activity from 1924 to 1930. In the subsequent century, there have been many excellent textbooks written on the topic, and one might well wonder why someone would decide to create another. The short answer is this: I’ve attempted to imagine, and then write, the book that would have made me happiest to read, if I were a graduate student today. Whether my choices of topics, explanations, and derivations work well for someone else is an entirely different and personal question, of course! Although this book aims to be a self-contained discussion, starting from the basics, it will probably be more readily accessible for those who have already taken undergraduate courses in classical mechanics, electromagnetism, and quantum mechanics. It is also assumed that the reader is already familiar with matrices and linear algebra, multivariable calculus, simple differential equations, the algebra of complex numbers, and basic concepts of probability. Quantum mechanics is a big subject, and it is not possible to cover everything. So I didn’t. Even so, there is more material in this book than can be reasonably covered in a typical academic year of lectures. This is intentional, because every course and every student will have different priorities. I did consider it essential to include certain modern subjects that are not always covered in o lder books at this level, notably the hidden-variables alternative, Bell inequalities, entangled subsystems and open systems, generalized measurements, decoherence, and quantum information. The instructor will likely have to make some hard choices of what to leave out, informed by the interests and preparation of the students. It would be impossible to draw up a universal plan for a course based on this book, appropriate for everyone. But at least I can offer the instructor and student a guide to those chapters and sections that are not prerequisites for later parts of the text. These can therefore be covered as topics of special interest, or not at all. In order of appearance: • Sections 5.7 and 8.8 on motion reversal (the transformation) and time reversal (the corresponding symmetry), which require antilinear and antiunitary operators • Section 9.3 on Landau levels for a charged particle in a magnetic field • Section 11.2 on the unbound states of Coulomb potentials • Section 15.4 on Brillouin–Wigner perturbation theory • Section 15.8 on almost-degenerate perturbation theory • Section 18.4 on multi-electron atoms • Chapter 19 on periodic potentials, Bloch waves, the Kronig–Penney model, and electronic band structure • Chapter 20 on the Born–Oppenheimer approximation, simple molecules, and quantization of rigid bodies • Chapter 23 on absorption and emission of light • Chapters 25 and 26 on the related topics of entanglement, subsystems and open systems, dynamical maps, the Lindblad equation, decoherence, and the emergence of classical behavior • Chapter 27, which is an invitation to the ideas of quantum information • Chapter 28 on relativistic quantum mechanics and the Dirac equation • Chapter 29 on the Feynman path integral approach, including the Ehrenberg– • Siday–Aharono v–Bohm effect and Dirac magnetic monopoles