Efthimios Kaxiras is the John Hasbrouck Van Vleck Professor of Pure and Applied Physics at Harvard University, Massachusetts. He holds joint appointments in the Department of Physics and the School of Engineering and Applied Sciences, and is an affiliate of the Department of Chemistry and Chemical Biology. He is the Founding Director of the Institute for Applied Computational Science, a Fellow of the American Physical Society and a Chartered Physicist and Fellow of the Institute of Physics, London. John D. Joannopoulos is the Francis Wright Davis Professor of Physics at Massachusetts Institute of Technology (MIT), where he is Director of the Institute for Soldier Nanotechnologies. He is a member of the National Academy of Sciences and American Academy of Arts and Sciences, a Fellow of the American Association for the Advancement of Science, a Fellow of the American Physical Society, and a Fellow of the World Technology Network. His awards include the MIT School of Science Graduate Teaching Award (1991), the William Buechner Teaching Prize of the MIT Department of Physics (1996), the David Adler Award (1997) and Aneesur Rahman Prize (2015) of the American Physical Society, and the Max Born Award of the Optical Society of America.