Enhancement in the cross-resonance gate performance

We theoretically model an experiment on a superconducting circuit made of a capacitively shunted flux qubit (CSFQ) and a transmon both capacitively coupled to a bus resonator in dispersive regime. We apply external driving microwave pulses over all energy levels and consider the transitions they impose effectively within the computational subspace. More specifically we apply entirely microwave two-qubit gate, the so called cross-resonance, on CSFQ at sweet spot and away from it. Interestingly the two-qubit fidelity is largely enhanced at certain external flux away from the sweet spot. This enhancement takes place as the result of suppressed leakage out of computational subspace.