30-Second Quantum Theory
Brian Clegg
(Icon Books, 2014)
Offers a more in-depth treatment of quantum physics without the in-depth mathematics.
Above and Below
Modern Physics for Everyone
Jack Challoner
(Explaining Science Publishing, 2017)
A wide-ranging tour of modern physics. It does not have the depth of The Atom, but it covers more ground, including relativity and cosmology.
The Cambridge Guide to the Material World
Rodney Cotterill
(Cambridge University Press, 1989)
This is an old book, and there are parts of it that are a little out of date—but it is a wonderful, intimate, comprehensive look at matter at the atomic scale. It is out of print, but secondhand copies are available online.
The Cell
A Visual Tour of the Building Block of Life
Jack Challoner
(Chicago University Press, 2016)
A sister publication to The Atom. Like this book, The Cell is a comprehensive but accessible tour of its subject.
QED
The Strange Theory of Light and Matter
Richard Feynman
(Penguin, 1990)
Adapted from a series of lectures on quantum electrodynamics, a theory of physics of which Feynman was a pioneer, this book explains clearly how light and electrons interact. It is the definitive introduction to QED.
Seven Brief Lessons on Physics
Carlo Rovelli
(Penguin, 2016)
This beautifully written book makes a range of complex subjects accessible, in seven easy “lessons.” The author is a working theoretical physicist.
A free, open, online course presented by the Massachusetts Institute of Technology. A series of in-depth video lectures that require some prior understanding of algebra.
https://ocw.mit.edu/courses/physics/8-04-quantum-physics-i-spring-2013/
or
by The Khan Academy
A free, online course that explains the principles of quantum physics clearly in a series of videos. Courses on many other areas of science are also available. Highly recommended. https://www.khanacademy.org/science/physics/quantum-physics
A free, open online course by the University of Edinburgh, Scotland, 2018. Only high-school physics understanding is required for this course, which takes the viewer through the steps that led to the discovery of the so-called "God particle."
https://www.class-central.com/course/futurelearn-the-discovery-of-the-higgs-boson-1259 or https://goo.gl/srsU6F