Demonstration of an All-Microwave Controlled-Phase Gate between Far-Detuned Qubits

A challenge in building large-scale superconducting quantum processors is to find the right balance between coherence, qubit addressability, qubit-qubit coupling strength, circuit complexity, and the number of required control lines. Leading all-microwave approaches for coupling two qubits require comparatively few control lines and benefit from high coherence but suffer from frequency crowding and limited addressability in multiqubit settings. Here, we overcome these limitations by realizing an all-microwave controlled-phase gate between two transversely coupled transmon qubits that are far detuned compared to the qubit anharmonicity. The gate is activated by applying a single strong microwave tone to one of the qubits, inducing a coupling between the two-qubit vertical bar f, g > and vertical bar g, e > states, with vertical bar g >, vertical bar e >, and vertical bar f > denoting the lowest energy states of a transmon qubit. Interleaved randomized benchmarking yields a gate fidelity of 97.5 +/- 0.3% at a gate duration of 126 ns, with the dominant error source being decoherence. We model the gate in presence of the strong drive field using Floquet theory and find good agreement with our data. Our gate constitutes a promising alternative to present two-qubit gates and could have hardware scaling advantages in large-scale quantum processors as it requires neither additional drive lines nor tunable couplers.