To see the world as a web of information is a recent view. Humanity has contemplated the source and character of our knowledge since the dawn of time, but the present technologically oriented civilization demands a more concrete concept. Knowledge has been replaced by information. The information has to be carried by physical objects, and these are described by the theories of physics. Thus, we have to develop a theory for information coded in physical objects.
Long ago, scientists developed formal descriptions of classical information transfer and its manipulation. Only recently, however, have we encountered the information capacity carried by quantum entities. The quantum theory of information, communication, and computing is rather recent. It has grown and matured at a surprising speed. Many discussions of physical observations and quantum measurements are today phrased in terms of information-theoretic concepts. Thus, there is a need to educate students in this thinking but also a need for established researchers to get acquainted with the new way of thinking provoked by the informational aspects of physics. The present book is written to fulfill this need. We consider our readership to be mainly physicists who want to absorb the basics of quantum information within the quantum mechanical framework with which they are familiar. For people who wish to work seriously on the topic or who have a nonphysicist background, many alternative sources are already available.