The robustness of robust phase estimation (RPE) relies on noise being below a particular threshold. While it is difficult or impossible to directly test the violation of this threshold, we developed a set of consistency checks that herald whether there might be violations in a data set. We tested these checks for common noise models and identified two that reliably identify the point in an RPE run beyond which further estimates cannot be trusted.
RPE is a powerful protocol for assessing the phase of a unitary without auxiliary qubits. To make use of it in the NISQ era we need methods for assessing whether experimental data meet its noise threshold requirements. We have developed and tested such methods, which will enable the adoption of RPE for quantum simulation and quantum characterization applications.
For details see “Consistency testing for robust phase estimation”, A. Russo, W. Kirby, K. Rudinger, A. Baczewski, & S. Kimmel. arXiv:2011.13442.
Also, supporting software is available on gitlab https://gitlab.com/quapack/pyrpe