Figure 9
From: Geometric control theory for quantum back-action evasion
![Figure 9](http://media.springernature.com/full/springer-static/image/art%3A10.1140%2Fepjqt%2Fs40507-016-0053-5/MediaObjects/40507_2016_53_Fig9_HTML.gif)
Normalized power spectral densities of the noise. The black solid line represents the SQL (35), and the dot-dashed blue line does the case without feedback. The dotted green and dashed red lines show the cases for the feedback controlled system, with coherent and squeezed probe field, respectively.