Scalable Interconnection Using a Superconducting Flux Qubit

To improve the performance of quantum computers, implementation technology that guarantees the scalability of the number of qubits is essential, and increasing the degrees of freedom in routing by 2.5-dimensional implementation is important for realizing the scalability of circuits. Here, we achieve long-distance coupling using a superconducting flux qubit enabling routing on the order of millimeters. We report the design for a reliable connection qubit with a proof-of-concept demonstration of quantum annealing. We perform experiments and simulations on suppressing errors due to coupling. The coupling status is strictly controllable, enabling elimination of crosstalk from the unintentional circuit region. A low-temperature flip-chip bonding technology is introduced for the 2.5-dimensional interconnection. The superconducting flux qubit, formed across two different chips via bumps, is demonstrated for the first time to show a state transition similar to that in a conventional qubit. The connection qubit and flip-chip bonding pave the way for new interconnections between different types of qubits. The possibility of interactions between gate-type qubits is investigated in a simulation.