Figure 13

Figure 13: Light field in a vacuum quantum state |vac⟩. Left panel (a) features a typical result one could get measuring the (normalized) electric field strength of the light wave in a vacuum state as a function of time. Right panel (b) represents a phase space picture of the results of measurement. A red dashed circle displays the error ellipse for the state |vac⟩ that encircles the area of single standard deviation for a two-dimensional random vector ˆa of measured light quadrature amplitudes. The principal radii of the error ellipse (equal in vacuum state case) are equal to square roots of the covariance matrix 𝕍vac eigenvalues, i.e., to √ -- 1∕ 2.