ABSTRACT
In this chapter, we will introduce different representations of
the electromagnetic (EM) field. One may ask, why do we need
different representations for the EMfield? The answer is that usually
we do not know the state of the EM field which in quantum
optics is represented by the annihilation and creation operators.
However, results of measurements of the field are given in terms
of real variables, for example, intensity. The representations allow
us to recognize the state of the field from values of the measured
quantities such as average amplitude, intensity, and correlation
functions. The nature of the state is present in terms of the
interpretation of the apparently classical (measured) variables.
We will discuss two basic types of representations often used in
quantum optics, Fock state (photon number) representation and
coherent states representation, the later one introduced by Glauber.a
We also discuss properties of fields with thermal and Poisson
distribution of photons. The photon number states are very often
used as a basis for quantum optics problems, and despite of many
difficulties have recently been generated experimentally [11-13].
