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Phys Rev Lett. 2008 Sep 12;101(11):117005. Epub 2008 Sep 12.

Phase-locking transition in a chirped superconducting Josephson resonator.

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Quantum Nanoelectronics Laboratory, Department of Physics, University of California, Berkeley, California 94720, USA.


We observe a sharp threshold for dynamic phase locking in a high-Q transmission line resonator embedded with a Josephson tunnel junction, and driven with a purely ac, chirped microwave signal. When the drive amplitude is below a critical value, which depends on the chirp rate and is sensitive to the junction critical current I0, the resonator is only excited near its linear resonance frequency. For a larger amplitude, the resonator phase locks to the chirped drive and its amplitude grows until a deterministic maximum is reached. Near threshold, the oscillator evolves smoothly in one of two diverging trajectories, providing a way to discriminate small changes in I0 with a nonswitching detector, with potential applications in quantum state measurement.

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