Feedback control of the fluorescence light squeezingA. Barchielli1, 2, M. Gregoratti1, 2 and M. Licciardo1
1 Mathematics Department, Politecnico di Milano - piazza Leonardo da Vinci 32, I-20133, Milano, Italy, EU
2 Istituto Nazionale di Fisica Nucleare - Sezione di Milano - Milano, Italy, EU
received 16 July 2008; accepted in final form 8 December 2008; published January 2009
published online 19 January 2009
We consider a trapped two-level atom stimulated by a coherent monochromatic laser and we study how to enhance the squeezing of the fluorescence light in the presence of a Wiseman-Milburn feedback mechanism, based on the homodyne detection of a fraction of the emitted light. We analyze the effect of the control parameters on the properties of the spectrum of light and we also discuss the relation between light squeezing and atomic states, which qualitatively changes when the control is present. We also show that feedback can produce sub-natural line narrowing of the fluorescence light, without the presence of squeezing in the stimulating light. The whole problem is tackled inside the framework of the quantum trajectory theory.
42.50.Dv - Quantum state engineering and measurements.
42.50.Lc - Quantum fluctuations, quantum noise, and quantum jumps.
03.65.Ta - Foundations of quantum mechanics; measurement theory.
© EPLA 2009