Practical implementation of Toffoli-based qubit rotation

The Toffoli gate is an important universal quantum gate, and will alongside the Clifford gates be available in future fault-tolerant quantum computing hardware. Many quantum algorithms rely on performing arbitrarily small single-qubit rotations for their function, and these rotations may also be used to construct any unitary from a limited (but universal) gate set. How to carry out such rotations is then of significant interest. In this work, we evaluate the performance of a recently proposed single-qubit rotation algorithm using the Clifford plus Toffoli gate set by implementation of a one-shot version on both a real and a simulated quantum computer. We test the algorithm under various simulated noise levels using a per-qubit depolarizing error noise model and examine how the probabilities and process fidelities are affected. We then conduct live runs and find that the results reasonably match the simulated results. We also attempt to model the hardware noise by combining a number of noise models, matching the results to results of the live runs to approximate the hardware noise. Our results suggest that the algorithm will perform well for up to 1% noise, under the noise models we chose. We further posit the use of our algorithm as a benchmark for quantum processing units, given that it has a low complexity that is easy to fine-tune in small steps. We provide details for how to do this.

💡 Research Summary

The paper presents an experimental study of a recently proposed algorithm for approximating arbitrary single‑qubit Z‑axis rotations using only Clifford and Toffoli gates. The authors implement a “one‑shot” version of the algorithm, which succeeds with probability greater than one‑half, on both a simulated quantum processor (Qiskit AerSimulator) and a real IBM quantum processing unit (ibm torino).

The theoretical background (Ref.