Thursday, December 18, 2008

Freezing Coherent Field Growth in a Cavity by the Quantum Zeno Effect

This is such an outstanding experiment and a testament to ingenuity of the experimenters.

A group in France has managed to show the Quantum Zeno effect in a rather "classical" system using a microwave cavity.[1]

Abstract: We have frozen the coherent evolution of a field in a cavity by repeated measurements of its photon number. We use circular Rydberg atoms dispersively coupled to the cavity mode for an absorption-free photon counting. These measurements inhibit the growth of a field injected in the cavity by a classical source. This manifestation of the quantum Zeno effect illustrates the backaction of the photon number determination onto the field phase. The residual growth of the field can be seen as a random walk of its amplitude in the two-dimensional phase space. This experiment sheds light onto the measurement process and opens perspectives for active quantum feedback.

They showed that even if the observation is "absorption free", the very act of such an observation will disrupt the phase of the microwave photons, causing the resonant build up to either be slower, or completely destroyed, depending on how often the observation is made.

Another experimental triumph of quantum mechanics!

[1] J. Bernu et al., Phys. Rev. Lett. 101, 180402 (2008).

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