Narrow Results

In quantum communication, feedback may be defined in a number of distinct ways. An analysis of the effect feedback has on the rate information may be communicated is given, and a number of results and conjectures are stated.

Quantum trajectory theory is the best mathematical set up to model continual observations of a quantum system and feedback based on the observed output. Inside this framework, we study how to enhance the squeezing of the fluorescence light emitted by a two-level atom, stimulated by a coherent monochromatic laser. In the presence of a Wiseman-Milburn feedback scheme, based on the homodyne detection of a fraction of the emitted light, we analyze the squeezing dependence on the various control parameters.

We calculate the geometric phase associated to a dissipative system which is influenced by system's state (feedback). The dependence of the geometric phase on the control feedback parameters is calculated and discussed. This direct feedback procedure can overcome spontaneous emission effect and generate a fluctuation on the geometric phase.