Real-time quantum feedback prepares and stabilizes photon number states

@article{Sayrin2011RealtimeQF,
  title={Real-time quantum feedback prepares and stabilizes photon number states},
  author={Cl{\'e}ment Sayrin and Igor Dotsenko and Xingxing Zhou and Bruno Peaudecerf and Th{\'e}o Rybarczyk and S. Gleyzes and Pierre Rouchon and Mazyar Mirrahimi and Hadis Amini and M. Brune and Jean-Michel Raimond and Serge Haroche},
  journal={Nature},
  year={2011},
  volume={477},
  pages={73-77}
}
Feedback loops are central to most classical control procedures. A controller compares the signal measured by a sensor (system output) with the target value or set-point. It then adjusts an actuator (system input) to stabilize the signal around the target value. Generalizing this scheme to stabilize a micro-system’s quantum state relies on quantum feedback, which must overcome a fundamental difficulty: the sensor measurements cause a random back-action on the system. An optimal compromise uses… 

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