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Elements of Quantum Computation and Quantum Communication by Anirban Pathak

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Chapter 1
Introduction and overview
Once upon a time there was a curious man. He knew nothing about the
subject called “Information Technology.” One day he visited a library and
suddenly saw a book entitled “Information Technology: The Art of Man-
aging Information. First, he thought: “This title is not for me. Let me
ignore it and look at the next title.” But then the curious man started
thinking: “What is it? What is information technology? What is informa-
tion? Why do I need to know how to manage it?” Since a curious man lives
in all of us, it would be tempting to follow the sequence of his thoughts
and try to answer these questions. Let us start with a simple question:
What is information technology? This question is very important as far
as this book or any other text related to information theory is concerned.
The simplest answer to this question is already provided in the title of that
book as: Information technology is the art of managing information. As
soon as we accept this particular definition, the other two questions that
appeared in his mind become extremely relevant. In this chapter, we will
try to answer those two questions and develop a quantitative perception
of classical and quantum information. Once a basic perception is built in
the first part of this chapter, we will describe a short history of quantum
computation and quantum communication at the end of this chapter.
1.1 What is information?
To a large extent, our general perception of information is qualitative. For
example, often after a lecture we say, “this talk was quite informative” or
“there was not much new information in this talk.” This type of qualita-
tive perception of information has been in existence from the beginning of
human civilization, but a clear definition of information was not present
until 1948. To begin with, we may define information as: Information is
something that we do not already know [1]. Some simple examples may
1

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