Extracting Coherent and Decoherent Qubit Errors Using Folded Cycles and K-body Noise Reconstruction

The accuracy of quantum computational results from today's Noisy Intermediate Scale Quantum (NISQ) hardware platforms is limited by a combination of errors arising entirely within the evolution of the quantum system coherent errors (r_coh ) and those associated with the evolution of the quantum system and its environment decoherent errors (r_decoh ). In this paper we rigorously develop a new efficient and scalable protocol that can separately compute both the coherent and decoherent contributions to the total infidelity of any Clifford operation of interest. Using the Lindblad equation, we derive a power law relationship for the propagation of coherent errors versus circuit depth. We test this derived analytical power law relationship using a two qubit CNOT and a single qubit combination to measure a complete set of error contributions in X, Y and Z using the K-Body Noise Reconstruction (KNR). With this information a curve fitting procedure was implemented to calculate the magnitude of the coherent error in this circuit. This protocol was tested and verified on several IBM gate-based superconducting hardware platforms. This new scalable protocol for independently measuring the contributions from the coherent and decoherent errors can be applied to both improve calibration routines for today's hardware platforms and provide helpful insights for enhancing the design of existing and future quantum architectures.