Physics – Condensed Matter – Mesoscale and Nanoscale Physics
Scientific paper
2008-05-14
Phys. Rev. Lett. 101, 117005 (2008)
Physics
Condensed Matter
Mesoscale and Nanoscale Physics
5 pages, 4 figures
Scientific paper
10.1103/PhysRevLett.101.117005
By coupling a harmonic oscillator to a quantum system it is possible to perform a dispersive measurement that is quantum non-demolition (QND), with minimal backaction. A non-linear oscillator has the advantage of measurement gain, but what is the backaction? Experiments on superconducting quantum bits (qubits) coupled to a non-linear Josephson oscillator have thus far utilized the switching of the oscillator near a dynamical bifurcation for sensitivity, and have demonstrated partial QND measurement. The detailed backaction associated with the switching process is complex, and may ultimately limit the degree to which such a measurement can be QND. Here we demonstrate a new dynamical effect in Josephson oscillators by which the bifurcation can be accessed without switching. When energized with a frequency chirped drive with an amplitude close to a sharp, phase-locking threshold, the oscillator evolves smoothly in one of two diverging trajectories - a pointer for the state of a qubit. The observed critical behavior agrees well with theory and suggests a new modality for quantum state measurement.
Aumentado José
Friedland Lazar
Naaman O.
Siddiqi Irfan
Wurtele Jonathan S.
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