Introduction to the Tenth Anniversary Edition
Quantum mechanics has the curious distinction of being simultaneously the most suc-
cessful and the most mysterious of our scientific theories. It was developed in fits and
starts over a remarkable period from 1900 to the 1920s, maturing into its current form in
the late 1920s. In the decades following the 1920s, physicists had great success applying
quantum mechanics to understand the fundamental particles and forces of nature, cul-
minating in the development of the standard model of particle physics. Over the same
period, physicists had equally great success in applying quantum mechanics to understand
an astonishing range of phenomena in our world, from polymers to semiconductors, from
superfluids to superconductors. But, while these developments profoundly advanced our
understanding of the natural world, they did only a little to improve our understanding
of quantum mechanics.
This began to change in the 1970s and 1980s, when a few pioneers were inspired to
ask whether some of the fundamental questions of computer science and information
theory could be applied to the study of quantum systems. Instead of looking at quantum
systems purely as phenomena to be explained as they are found in nature, they looked at
them as systems that can be designed.Thisseemsasmallchangeinperspective,butthe
implications are profound. No longer is the quantum world taken merely as presented,
but instead it can be created. The result was a new perspective that inspired both a
resurgence of interest in the fundamentals of quantum mechanics, and also many new
questions combining physics, computer science, and information theory. These include
questions such as: what are the fundamental physical limitations on the space and time
required to construct a quantum state? How much time and space are required for a given
dynamical operation? What makes quantum systems difficult to understand and simulate
by conventional classical means?
Writing this book in the late 1990s, we were fortunate to be writing at a time when
these and other fundamental questions had just crystallized out. Ten years later it is
clear such questions offer a sustained force encouraging a broad research program at the
foundations of physics and computer science. Quantum information science is here to
stay. Although the theoretical foundations of the field remain similar to what we discussed
10 years ago, detailed knowledge in many areas has greatly progressed. Originally, this book
served as a comprehensive overview of the field, bringing readers near to the forefront
of research. Today, the book provides a basic foundation for understanding the field,
appropriate either for someone who desires a broad perspective on quantum information
science, or an entryway for further investigation of the latest research literature. Of course,