Summary
In the seventh and last lesson, we described the principle of an experiment to prepare and protect a non-classical state of a harmonic oscillator from decoherence, using aquantum feedback method. The control of physical systems in our daily lives is generally based on classical feedback methods. The temperature of a building, the speed of a vehicle, the altitude of an airplane are measured by probes whose data is sent to computers which evaluate the correction needed to bring the controlled quantities back to their optimum values. Extending this principle to the microscopic world is essential for quantum information processing, which uses real or artificial atoms and photons as elementary building blocks. The fundamental difficulty with quantum feedback is that the measurement of the system itself randomly disturbs the controlled system.
