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Implementation of a generalized controlled-NOT gate between fixed-frequency transmons

TitleImplementation of a generalized controlled-NOT gate between fixed-frequency transmons
Publication TypeJournal Article
Year of Publication2019
AuthorsS. P. Premaratne, J-H. Yeh, F.. C. Wellstood, and B.. S. Palmer
JournalPhys. Rev. A
Date PublishedJAN 11
Type of ArticleArticle

We have embedded two fixed-frequency Al/AlOx/Al transmons, with ground-to-excited transition frequencies at 6.0714 and 6.7543 GHz, in a single three-dimensional Al cavity with a fundamental mode at 7.7463 GHz. Strong coupling between the cavity and each transmon results in an effective qubit-qubit coupling strength of 26 MHz and a -1 MHz dispersive shift in each qubit's transition frequency, depending on the state of the other qubit. Using the all-microwave SWIPHT (speeding up wave forms by inducing phases to harmful transitions) technique {[}Economou and Barnes, Phys. Rev. B 91, 161405 (2015)], we demonstrate the operation of a generalized controlled-NOT gate between the two qubits, with a gate time of tau(g) = 907 ns optimized for this device. Using quantum process tomography we find that the gate fidelity is 83-84%, somewhat less than the 87% fidelity expected from relaxation and dephasing in the transmons during the gate time.