Context-aware fidelity estimation

Abstract

We present context-aware fidelity estimation (CAFE), a framework for benchmarking quantum operations that offers several practical advantages over existing methods such as randomized benchmarking (RB) and cross-entropy benchmarking. In CAFE, a gate or a subcircuit from some target experiment is repeated n times before being measured. By using a subcircuit, we account for effects from the spatial and temporal circuit context. Since coherent errors accumulate quadratically while incoherent errors grow linearly, we can separate them by fitting the measured fidelity as a function of n. One can additionally interleave the subcircuit with dynamical decoupling sequences to remove certain coherent error sources from the characterization when desired. We have used CAFE to experimentally validate our single- and two-qubit unitary characterizations by measuring fidelity against estimated unitaries. In numerical simulations, we find that CAFE produces fidelity estimates at least as accurate as interleaved RB while using significantly fewer resources. We also introduce a compact formulation for preparing an arbitrary two-qubit state with a single entangling operation and use it to present a concrete example using CAFE to study controlled-Z gates in parallel on a Sycamore processor.