Suppressing error correlations in space and time using quantum control

We perform measurements of spatio-temporal error correlations in linear arrays of trapped ions. Experiments demonstrate that slow drifts and systematic calibration errors arising from microwave amplifiers, quasi-static magnetic field gradients, and spatial microwave inhomogeneities contribute to operational errors at the 10^-4 level over chains up to seven ions. By replacing standard "primitive" microwave gate operations on the 12.6 GHz hyperfine qubit in ¹⁷¹Yb⁺ we demonstrate an ability to reduce error correlations due to these native error sources. Measurements of randomized benchmarking on individual ions show that even when overall error rates are reduced only marginally, signatures of temporal error correlations are reduced through use of noise-filtering controls. Moreover, we demonstrate that the measured correlations between errors on neighboring qubits are reduced when appropriate control solutions are employed. These experiments demonstrate an important role for quantum control operations in the context of quantum error correction even when the added complexity of the error-suppressing controls limits the absolute suppression of error rates in the system.