We experimentally demonstrate a virtual two-qubit gate and characterize it using quantum process tomography~(QPT). The virtual two-qubit gate decomposes an actual two-qubit gate into single-qubit unitary gates and projection gates in quantum circuits for expectation-value estimation. We implement projection gates via mid-circuit measurements. The deterministic sampling scheme reduces the number of experimental circuit evaluations required for decomposing a virtual two-qubit gate. We also apply quantum error mitigation to suppress the effect of measurement errors and improve the average gate fidelity of a virtual controlled-Z (CZ) gate to fav=0.9938±0.0002. Our results highlight a practical approach to implement virtual two-qubit gates with high fidelities, which are useful for simulating quantum circuits using fewer qubits and implementing two-qubit gates on a distant pair of qubits.
@article{arxiv.2307.03232,
title = {Experimental demonstration of a high-fidelity virtual two-qubit gate},
author = {Akhil Pratap Singh and Kosuke Mitarai and Yasunari Suzuki and Kentaro Heya and Yutaka Tabuchi and Keisuke Fujii and Yasunobu Nakamura},
journal= {arXiv preprint arXiv:2307.03232},
year = {2024}
}