Course Overview: https://youtu.be/xyF-MmGNxd0 The 20th century was known as the century of physics. In the past 120 years, concepts such as space, time, energy, entropy and particles were understood to much deeper levels. New paradigms of thinking such as relativity and quantum mechanics emerged. This course is the second course in the Understanding Modern Physics series, which covers an introduction to quantum mechanics, atomic physics and quantum information. We will find (i) How the quantum world is different from our everyday experience, and why we need quantum mechanics; (ii) How to describe atoms in fundamental physics, why atoms do not collapse, and what are the atomic states; (iii) The nature of quantum information, and why quantum information is much richer than classical information.