A strongly coupled two-qubit system with weak quantum crosstalk

In microwave-activated two-qubit gate schemes, a strong static exchange interaction between superconducting qubits leads to a strong hybridization between their eigenstates and thus enables fast operations. However, a larger exchange-interaction strength generally increases spurious quantum (ZZ) crosstalk, diminishing addressability for single-qubit gates. In this talk, we discuss the design of a system of transmons with multiple coupling paths between qubits, which provides a high entangling-gate rate with reduced static quantum crosstalk. We optimize the layout configuration of such a system by means of a finite-element analysis combined with the energy-participation-ratio technique [1]. This approach allows us to find the quantum Hamiltonian for a given physical layout and therefore accurately estimate the ZZ coupling magnitude as well as the rates of two-qubit gates.

[1] Z. Minev, et.al., npj Quantum Inf. 7, 131 (2021)