Co-authors: Landry Bretheau (Ecole Normale Superieure, Paris, France), Philippe Campagne-Ibarcq (Ecole Normale Superieure, Paris, France), Emmanuel Flurin (Ecole Normale Superieure, Paris, France), Francois Mallet (Ecole Normale Superieure, Paris, France)
In the strong coupling regime of circuit-QED, a qubit can be used as a photocounter. Leading to a binary response only, it is possible to probe whether or not the cavity has N photons for any number N we choose. By repeatedly asking this question, it is possible to freeze the evolution of the cavity mode by Zeno effect into either the number state |N> or the space generated by all the other states. Allowing resonant driving and starting from the ground state of the cavity, this Zeno blockade is thus similar to a transformation of the oscillator into an N/2 spin. Interestingly, one can also produce the same blockade without any dissipation or readout by driving the qubit at the resonance frequency it exhibits when the cavity is in state |N>. We have realized this blockade using superconducting circuits and measured the photon number distribution and Wigner function of the cavity mode as a function of time, while driving the effective N/2 spin. Interesting non-classical s tates develop during the evolution.
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