Advanced FLUXONICS Process CJ2 Based on Sub-µm-Sized Cross-Type Nb/AlOx/Nb Josephson Junctions for Mixed Signal Circuits

Quantum computers represent a prominent example of technology harnessing quantum phenomena for practical applications. Implementations based on superconducting solid-state qubits play a leading role. These have facilitated the implementation of the first commercially viable quantum computers through the use of well-established and scalable fabrication technologies. As the number of qubits in these systems is continuously increasing, there is an urgent need to advance wiring and integration methods. Specifically, the demand for high-frequency control and readout lines within the millikelvin coolers introduces unwanted heat load. As a scalable alternative, superconducting digital electronics has been proposed as a promising candidate for direct interfacing with superconducting quantum circuits. We, therefore, advanced our well-established cross-type, sub-micrometer-sized Nb-based Josephson junction technology for analog circuits to allow for the implementation of digital circuits. Thus, an advanced mixed signal process CJ2 hosts both, analog and digital circuits, on a single chip, using Josephson junctions of a wide critical current range. We discuss the technology and the realization of first circuits as well as results of basic logic gate and dc-SQUID operations. This advanced technology CJ2 enables the development of digital interfaces for quantum circuits by academic and industrial partners in the framework of the European FLUXONICS foundry.