A First Introduction to Quantum Physics In this undergraduate textbook the author develops the quantum theory from first principles based on very simple experiments: a photon travelling through beam splitters to detectors an electron moving through a Stern Gerlach machine and an atom emitting radiation. From the physical description of these experiments follows a natural mathematical description in terms of matrices and complex numbers. The first part of the book examines how experimental facts force us to let go of some deeply held preconceptions and develops this idea into a mathematical description of states probabilities observables and time evolution using physical applications. The second part of the book explores more advanced topics including the concept of entanglement the process of decoherence and extension of the quantum theory to the situation of a particle in a one dimensional box. Here the text makes contact with more traditional treatments of quantum mechanics. The remaining chapters delve deeply into the idea of uncertainty relations and explore what the quantum theory says about the nature of reality. The book is an ideal and accessible introduction to quantum physics with modern examples and helpful end of chapter exercises Chapter 1: Three simple experiments The purpose of physical theories A laser and a detector A laser and a beam splitter A Mach Zehnder interferometer The breakdown of classical concepts Chapter 2: Photons and Interference Photon paths and superpositions The beam splitter as a matrix The phase in an interferometer How to calculate probabilities Gravitational wave detection Chapter 3: Electrons with Spin The Stern Gerlach experiment The spin observable The Bloch sphere The uncertainty principle Magnetic resonance imaging Chapter 4: Atoms and Energy The energy spectrum of atoms Changes over time The Hamiltonian Interactions Atomic clocks Chapter 5: Operators Eigenvalue problems Observables Evolution The commutator Projectors Chapter 6: Entanglement The state of two electrons Entanglement Quantum teleportation Quantum computers Chapter 7: Decoherence Classical and quantum uncertainty The density matrix Interactions with the environment Entropy and Landauer’s principle Chapter 8: The Motion of Particles A particle in a box The momentum of a particle The energy of a particle The scanning tunneling microscope Chemistry Chapter 9: Uncertainty Relations Quantum uncertainty revisited Position momentum uncertainty The energy time uncertainty relation The quantum mechanical pendulum Precision measurements Chapter 10: The Nature of Reality The emergent classical world The quantum state revisited Nonlocality Contextuality A compendium of interpretations