Correlators exceeding one in continuous measurements of superconducting qubits
arXiv:1809.04222 · doi:10.1103/PhysRevLett.122.223603
Abstract
We consider the effect of phase backaction on the correlator for the output signal from continuous measurement of a qubit. We demonstrate that the interplay between informational and phase backactions in the presence of Rabi oscillations can lead to the correlator becoming larger than 1, even though . The correlators can be calculated using the generalized "collapse recipe" which we validate using the quantum Bayesian formalism. The recipe can be further generalized to the case of multi-time correlators and arbitrary number of detectors, measuring non-commuting qubit observables. The theory agrees well with experimental results for continuous measurement of a transmon qubit. The experimental correlator exceeds the bound of 1 for a sufficiently large angle between the amplified and informational quadratures, causing the phase backaction. The demonstrated effect can be used to calibrate the quadrature misalignment.
arXiv comment11 pages, 8 figures
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