Fixed-Frequency Qubits Coupled via a Tunable Bus

Stefan Filipp, David C. McKay, Easwar Magesan +3 more

Ji Chu, Fei Yan

David C. McKay, Stefan Filipp, Antonio Mezzacapo +3 more

The authors address a critical scalability issue in quantum computer design by activating a resonant exchange interaction. They achieve this by coupling two fixed-frequency superconducting qubits with a bus that is modulated at the frequency difference between the qubits. This yields a high-fidelity iSWAP entangling gate, which is sought as an important component for fault-tolerant quantum circuits in the surface-code architecture. The general nature of the interaction also suggests applications in quantum simulation, annealing, and bath engineering.

J. Stehlik, D. M. Zajac, Devin Underwood +9 more

Implementation of high-fidelity 2-qubit operations is a key ingredient for scalable quantum error correction. In superconducting qubit architectures, tunable buses have been explored as a means to higher-fidelity gates. However, these buses introduce new pathways for leakage. Here we present a modified tunable bus architecture appropriate for fixed-frequency qubits in which the adiabaticity restrictions on gate speed are reduced. We characterize this coupler on a range of 2-qubit devices, achieving a maximum gate fidelity of 99.85%. We further show the calibration is stable over one day.

Radoslaw C. Bialczak, M. Ansmann, M. Hofheinz +7 more