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-qubit coupling strength, and the number of required control lines. Leading all-microwave approaches for coupling two qubits require comparatively few control lines and maintain qubit coherence during the gate, but suffer from frequency crowding and limited addressability in multi-qubit settings. Here, we overcome these limitations by realizing an all-microwave controlled-phase gate between two transmon qubits which are far detuned compared to the qubit anharmonicity [1]. The gate is activated by applying a single, strong microwave tone to one of the qubits, inducing a coupling between the two-qubit |f,g〉 and |g,e〉 states. We model the gate in presence of the strong drive field using Floquet theory. Our gate could have hardware scaling advantages in large-scale quantum processors as it neither requires additional drive lines nor tunable couplers.
[1] Krinner, Kurpiers et al., Phys. Rev. Applied 14, 044039 (2020)