High-Density Qubit Wiring: Pin-Chip Bonding for Fully Vertical Interconnects

Abstract: Large-scale quantum computers with more than $10^5$ qubits will likely be built within the next decade. Trapped ions, semiconductor devices, and superconducting qubits among other physical implementations are still confined in the realm of medium-scale quantum integration ($\sim 100$ qubits); however, they show promise toward large-scale quantum integration. Building large-scale quantum processing units will require truly scalable control and measurement classical coprocessors as well as suitable wiring methods. In this blue paper, we introduce a fully vertical interconnect that will make it possible to address $\sim 10^5$ superconducting qubits fabricated on a single silicon or sapphire chip: Pin-chip bonding. This method permits signal transmission from DC to $\sim 10$ GHz, both at room temperature and at cryogenic temperatures down to $\sim 10$ mK. At temperatures below $\sim 1$ K, the on-chip wiring contact resistance is close to zero and all signal lines are in the superconducting state. High-density wiring is achieved by means of a fully vertical interconnect that interfaces the qubit array with a network of rectangular coaxial ribbon cables. Pin-chip bonding is fully compatible with classical high-density test board applications as well as with other qubit implementations.