Figure 15: Light field in a coherent quantum state . Left panel a) features a typical result
one could get measuring the (normalized) electric field strength of the light wave in a coherent state
as a function of time. Right panel b) represents a phase space picture of the results of measurement.
The red dashed line in the left panel marks the mean value . The red arrow in the right panel
features the vector of the mean values of quadrature amplitudes, i.e., , while the red dashed circle
displays the error ellipse for the state that encircles the area of single standard deviation
for a two-dimensional random vector of quadrature amplitudes. The principle radii of the error
ellipse (equal in the coherent state case) are equal to square roots of the covariance matrix ,
i.e., to .
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