Implementation of a conditional-phase gate by using in-situ tunable ZZ-interactions

High fidelity two-qubit gates exhibiting low crosstalk are essential building blocks for gate-based quantum information processing. In superconducting circuits two-qubit gates are typically based either on RF-controlled interactions or on the in-situ tunability of qubit frequencies. Here, we present an alternative approach using a tunable ZZ-interaction between two-qubits, mediated by a flux-tunable coupler element. By adding a direct capacitive coupling path between the qubits, we are able to control the ZZ-coupling rate over three orders of magnitude. Using this coupling mechanism we implement a conditional-phase gate without relying on resonant exchange of excitations and characterize its performance in terms of gate fidelity, leakage and residual coupling in the idle configuration.