Enhancement of field squeezing using coherent feedback

The theory of quantum feedback networks has recently been developed with the aim of showing how quantum input-output components may be connected together so as to control, stabilize, or enhance the performance of one of the subcomponents. In this paper, we show how the degree to which an idealized component (a degenerate parametric amplifier in the strong-coupling regime) can squeeze input fields may be enhanced by placing the component in loop in a simple feedback mechanism involving a beam splitter. We study the spectral properties of output fields, placing particular emphasis on the elastic and inelastic components of the power density.

Figure 1

(Color online) Squeezing device in a feedback loop.

Figure 2

Input-output component.

Figure 3

Feedback using a beam splitter.

Figure 4

Feedback with loss.