  This article is a short review on the concept of information. We show the
strong relation between Information Theory and Physics, beginning by the
concept of bit and its representation with classical physical systems, and then
going to the concept of quantum bit (the so-called ``qubit'') and exposing some
differences and similarities. This paper is intended to be read by
non-specialists and undergraduate students of Computer Science, Mathematics and
Physics, with knowledge of Linear Algebra and Quantum Mechanics.
