ZZ Amplification Using A Fluxonium Coupler With A Large ON/OFF Ratio

A system and method provide a configurable quantum logic gate. The system includes two fixed-frequency transmon qubits that are capacitively coupled to each other and to a tunable fluxonium coupler. Applying a magnetic flux to the coupler results in a controlled decrease in the ZZ interaction between the two transmon qubits. When the two transmon qubits have a small, positive ZZ interaction without any field present, applying a particular flux to the coupler effectively eliminates the interaction. Applying a larger flux produces a large, negative ZZ interaction that results in an avoided level crossing at an operational frequency. Appropriate choice of the applied flux permits implementation of, among other things, an adiabatic controlled Z (CZ) gate having high fidelity and low complexity.