Experimental demonstration of coherent feedback control on optical field   squeezing
  Coherent feedback is a non-measurement based, hence a back-action free, method of control for quantum systems. A typical application of this control scheme is squeezing enhancement, a purely non-classical effect in quantum optics. In this paper we report its first experimental demonstration that well agrees with the theory taking into account time delays and losses in the coherent feedback loop. The results clarify both the benefit and the limitation of coherent feedback control in a practical situation. 
Sanae Iida, Mitsuyoshi Yukawa, Hidehiro Yonezawa, Naoki Yamamoto and   Akira Furusawa
quant-ph