Suppression of Qubit Crosstalk between Transmons and Capacitively Shunted Flux Qubits: Part 2, Theory

We compare two-qubit superconducting circuits composed of either different-species qubits or all-transmon qubits. In the different-species case, we use qubits with the opposite sign of anharmonicity, while for the all-transmon circuit, both qubits have a negative anharmonicity. We show that there are unique features in the different-species approach that makes it attractive for use in near-term quantum computers. Circuits with different-species qubits are capable of fast two-qubit gates and they allow for complete cancellation of ZZ crosstalk interactions. Our theoretical results are in agreement with an experiment on a two-qubit device consisting of a capacitively shunted flux qubit and a transmon and show a promising way to improve two-qubit gate operations.