Tomographic characterization of quantum gates with error amplification

Characterization of gate error is a fundamental step toward improvement of gate accuracy. Quantum tomography is an attractive class of characterization protocols along with the direction because it provides several information of errors, but its standard protocol suffers from low reliability originated from state-and-measurement (SPAM) error. Advanced tomographic protocols such as gate-set tomography, idle tomography, and Hamiltonian error-amplifying tomography use an error-amplification process to overcome the low reliability. One disadvantage of the use of error-amplification is an increase in computational cost and instability of data-fitting because of its high nonlinearity with respect to fitting parameters. Here we propose a new data-processing method (estimator) for quantum tomographic protocols with error-amplification, which enables us to reduce computational cost and instability of data-fitting. We theoretically and numerically show that the method proposed has sufficiently high reliability in practical situation for development of quantum computer.