ABSTRACT
In Chapter 4 we defined different representations of the elec-
tromagnetic (EM) field: the Fock, thermal and coherent state
representations, and discussed in details properties of the EM field
in these representations. We have seen that in the coherent state
the fluctuations in the two quadratures of the EM field amplitudes
are equal and minimize the uncertainty product given by the
Heisenberg’s uncertainty relation. In other words, the quantum
fluctuations of the field in a coherent state are equal to the zero-
point fluctuations and are randomly distributed in phase. These
zero-point fluctuations represent the standard quantum limit to the
reduction of noise in a signal. Even an ideal laser operating in a pure
coherent state would still possess quantum noise due to zero-point
fluctuations.
