Experimental demonstration of a high-fidelity virtual two-qubit gate
Akhil Pratap Singh, Kosuke Mitarai, Yasunari Suzuki, Kentaro Heya, Yutaka Tabuchi, Keisuke Fujii, Yasunobu Nakamura
Abstract
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 midcircuit 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-<a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mi>Z</a:mi></a:math> (CZ) gate to <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mrow><b:msub><b:mi>f</b:mi><b:mi>av</b:mi></b:msub><b:mo>=</b:mo><b:mn>0.9938</b:mn><b:mo>±</b:mo><b:mn>0.0002</b:mn></b:mrow></b:math>. 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. Published by the American Physical Society 2024