Cross-resonance interactions between superconducting qubits with variable detuning

The cross-resonance effect is a promising route for generating two-qubit gates in an all-microwave architecture based on superconducting qubits. Because the strength of the cross-resonance effect, and hence the speed of a two-qubit gate, depends sensitively on the detuning between the qubits and the anharmonicity of each qubit, we are performing experiments with some fixed-frequency transmon qubits and others with some tunability. By using asymmetric transmon qubits, we are able to vary this detuning over a moderate range. This allows us to study the cross-resonance effect while varying the magnetic flux to generate different qubit-qubit detunings.