Dr. Jean Michel Raymond
Pierre and Marie Curie University and Kastler Brossel Laboratory, Dept. of Physics (ENS, Paris)
Conference room Querzoli - LENS - via Nello Carrara 1 - Sesto Fiorentino (Florence)
Published on-line at 10:28:10 AM on Saturday, February 18th, 2012
Atoms and cavities: quantum measurement and feedback
Quantum feedback techniques allow high-quality counting of the number of photons in a box and open new perspectives for quantum information manipulations.
We perform an ideal counting of the number of photons in a photon box with an unprecedented quality. The microwave field is probed by a series of highly sensitive circular Rydberg atoms. The number of photons is finally precisely determined, and the photons are not absorbed as in standard photo-detections. This projective measurement illustrates all quantum postulates.
It naturally leads to the preparation of non-classical photon number states. Due to cavity damping, they undergo a fast decoherence. We can follow in real time the quantum jumps of light revealing this relaxation process. The photon number states can be protected against decoherence by quantum feedback. It extends the principle of classical feedback loops to the quantum realm.
We use information provided by the atoms to react in real time onto the field state and maintain a constant photon number, in spite of decoherence and in spite of the unavoidable perturbation induced by the measurement itself. Stabilizing non-classical states opens interesting perspectives for quantum information manipulations (photo credit: Michel Brune, "Quantum feedback or the art of juggling with photons").
Klein colloquium by Dr. Pietro Lombardi: "Reading the relative phase between two laser pulses with a multi-path atom interferometer".
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