Experimental demonstration of fully coherent quantum feedback

In the conventional picture of quantum feedback, control sensors make measu rements on a quantum system, a classical controller processes the results o f the measurements, and semiclassical actuators act back on the system to a lter its behavior. We describe and provide an experimental demonstration of an alternative method for quantum feedback control, in which the sensors, controller, and actuators of conventional feedback control are replaced wit h quantum systems that interact coherently with the system to be controlled . The resulting control system represents a fully coherent quantum feedback loop.