Demonstration of Robust Quantum Gate Tomography via Randomized Benchmarking

TL;DR

This paper demonstrates a robust quantum gate tomography method called randomized benchmarking tomography (RBT) in superconducting qubits, overcoming self-consistency issues and accurately reconstructing quantum gates including non-Clifford unitaries.

Contribution

The paper implements RBT with experimental improvements in superconducting qubits, enabling accurate, self-consistent quantum gate reconstruction including non-Clifford gates.

Findings

Successful implementation of RBT in superconducting qubits.

Accurate reconstruction of single-qubit gates, including non-Clifford unitaries.

Reconstructed gate fidelities consistent with randomized benchmarking results.

Abstract

Typical quantum gate tomography protocols struggle with a self-consistency problem: the gate operation cannot be reconstructed without knowledge of the initial state and final measurement, but such knowledge cannot be obtained without well-characterized gates. A recently proposed technique, known as randomized benchmarking tomography (RBT), sidesteps this self-consistency problem by designing experiments to be insensitive to preparation and measurement imperfections. We implement this proposal in a superconducting qubit system, using a number of experimental improvements including implementing each of the elements of the Clifford group in single `atomic' pulses and custom control hardware to enable large overhead protocols. We show a robust reconstruction of several single-qubit quantum gates, including a unitary outside the Clifford group. We demonstrate that RBT yields physical gate reconstructions that are consistent with fidelities obtained by randomized benchmarking.