Efficient reconstruction, benchmarking and validation of cross-talk
  models in readout noise in near-term quantum devices
Readout errors contribute significantly to the overall noise affecting
present-day quantum computers. However, the complete characterization of
generic readout noise is infeasible for devices consisting of a large number of
qubits. Here we introduce an appropriately tailored quantum detector tomography
protocol, the so called Quantum Detector Overlapping Tomography, which enables
efficient characterization of $k-$local cross-talk effects in the readout noise
as the sample complexity of the protocol scales logarithmically with the total
number of qubits. We show that QDOT data provides information about suitably
defined reduced POVM operators, correlations and coherences in the readout
noise, as well as allows to reconstruct the correlated clusters and neighbours
readout noise model. Benchmarks are introduced to verify utility and accuracy
of the reconstructed model. We apply our method to investigate cross-talk
effects on 79 qubit Rigetti and 127 qubit IBM devices. We discuss their readout
noise characteristics, and demonstrate effectiveness of our approach by showing
superior performance of correlated clusters and neighbours over models without
cross-talk in model-based readout error mitigation applied to energy estimation
of MAX-2-SAT Hamiltonians, with the improvement on the order of 20% for both
devices.
Jan Tuziemski Filip B. Maciejewski Joanna Majsak Oskar Słowik Marcin Kotowski Katarzyna Kowalczyk-Murynka Piotr Podziemski Michał\ Oszmaniec