Abstract
High operation speed and low energy consumption may allow the superconducting digital single-flux-quantum circuits to outperform traditional complementary metal–oxide–semiconductor logic. The remaining major obstacle towards high element densities on-chip is a relatively large cell size necessary to hold a magnetic flux quantum Φ0. Inserting a π-type Josephson junction1,2 in the cell is equivalent to applying flux Φ0/2 and thus makes it possible to solve this problem3. Moreover, using π-junctions in superconducting qubits may help to protect them from noise4,5. Here we demonstrate the operation of three superconducting circuits—two of them are classical and one quantum—that all utilize such π-phase shifters realized using superconductor/ferromagnet/superconductor sandwich technology6. The classical circuits are based on single-flux-quantum cells, which are shown to be scalable and compatible with conventional niobium-based superconducting electronics. The quantum circuit is a π-biased phase qubit, for which we observe coherent Rabi oscillations. We find no degradation of the measured coherence time compared to that of a reference qubit without a π-junction.
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Acknowledgements
This work was supported by the EU projects EuroSQIP and MIDAS. We acknowledge support by the Deutsche Forschungsgemeinschaft (DFG), the joint grant of DFG and Russian Foundation of Basic Research, the Russian Federal Agency of Science and Innovations, and the State of Baden–Württemberg through the DFG Center for Functional Nanostructures (CFN).
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A.K.F., V.A.O., V.V.R., A.B.Z. and A.V.U. contributed with ideas for the experiments. A.K.F., V.A.O., V.V.B., J.L., M.K., D.B. and V.P.K. designed samples. V.A.O., A.N.R., M.K., D.B. and P.N.D. fabricated samples. A.K.F., V.V.B., V.A.O., J.L., S.P., M.K. and D.B. carried out experiments and analysed the experimental data. A.K.F. made theoretical estimations. A.V.U., J.L., V.V.R. and A.B.Z. did most of the writing. All of the authors discussed the results and the manuscript extensively.
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Feofanov, A., Oboznov, V., Bol’ginov, V. et al. Implementation of superconductor/ferromagnet/ superconductor π-shifters in superconducting digital and quantum circuits. Nature Phys 6, 593–597 (2010). https://doi.org/10.1038/nphys1700
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DOI: https://doi.org/10.1038/nphys1700
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