Pauli gate error amplification for sophisticated quantum gate calibration

Abstract

Improving quantum gate fidelity is one of the most important challenges for the development of quantum computers. Sophisticated calibration technique can eliminate coherent errors due to imperfection of quantum gates. To calibrate parameters of underlying pulses, we need to evaluate an error from the target unitary and optimize the parameters to minimize the error. To further improve the gate fidelity, we need to investigate smaller error terms with higher accuracy. Hamiltonian error amplifying tomography is one of techniques to investigate such smaller errors with the aid of echo sequence that selectively amplifies error terms of interest. However, the target quantum gate is restricted to specific form. In this work we demonstrate a novel echo sequence generation technique that enables us to amplify any small Pauli error term in any target Pauli gate. The presented technique was implemented using open-source software toolkits in Qiskit and we experimentally investigated small interaction terms in the cross-resonance gate of IBM Quantum devices.