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Breaking Bad: Quantum Verification in Correlated Noise Environments

Thursday March 30, 2017
3:30 pm

 Presenter:  Michael J. Biercuk, University of Sydney
 Series:  CQuIC Seminars
 Abstract:  Growth in the complexity and capabilities of quantum information hardware requires the availability of practical techniques for performance verification which function under realistic laboratory conditions. In this work we experimentally characterize the impact of common temporally correlated noise processes on both randomized benchmarking and gate-set tomography (GST). We study these protocols using a unified analytic toolkit based on an input-output formalism mapping (input) noise to (output) aggregate errors for arbitrary sequences of Clifford operations [1]. Our analysis highlights the role of sequence structure in enhancing or suppressing the sensitivity of quantum verification protocols to noise processes exhibiting strong temporal correlations; this sensitivity is absent when noise is uncorrelated, in line with standard assumptions underlying QCVV theory. We perform experiments with single trapped ions and inject tunable engineered noise, validating the central prediction that the distribution of measured fidelities over sequences in randomized benchmarking is described by a long-tailed gamma distribution across a wide range of noise models. The same analytic framework is then applied to GST to reveal the relative insensitivity of this procedure to strongly correlated noise proportional to $sigma_{z}$; we use GST's in-built numeric toolkits and experiments to demonstrate that GST systematically underestimates reported diamond norms by factors of up to 100x in the presence of such errors. Finally, we use these insights to experimentally demonstrate, for the first time, that dynamically corrected gate protocols suppress not only error rates in single gates, but also the correlation between residual errors in sequentially applied gates.

[1] Harrison Ball, Thomas M. Stace, Steven T. Flammia, and Michael J. Biercuk, "Effect of noise correlations on randomized benchmarking," Phys. Rev. A 93, 022303 (2016)
 Location:  Room 190, Physics & Astronomy

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