AVS 71 Session QS2-MoM: Systems, Devices, and Manufacturing Technologies for Quantum Technology

Superconducting qubits are leading candidates in the race to build a quantum computer capable of realizing computations beyond the reach of modern supercomputers. Within this modality, the ability to robustly and reliably fabricate high-quality, quantum-compatible circuits is critical both for fundamental research efforts and for more complex and capable quantum processors.MIT Lincoln Laboratory has worked over the course of two decades to establish, and continually expand and improve, superconducting qubit fabrication capabilities.Recently, we have piloted a superconducting foundry model to enable the US quantum research and development community to leverage the most robust and reliable of these capabilities in order to accelerate research progress.This presentation will provide an overview of superconducting qubit fabrication at MIT Lincoln Laboratory, describe its transition from 50 mm prototyping tools to 200 mm fabrication to support an expanded user base, and provide perspectives on how to support and enable the broader quantum research community as the variety and complexity of questions at the research frontier continues to expand.

Voltage tunable Josephson junctions (JJs) based on planar semiconductor quantum wells have potential to realize voltage tunable qubits fabricated at scale. Josephson junctions are fabricated from undoped Germanium quantum wells (Ge-QWs), grown by Molecular Beam Epitaxy (MBE), with carrier mobility greater than 40,000 cm²/Vs and hole density less than 1x10¹² cm^-2. These junctions use epitaxial aluminum to make transparent contact to the Ge-QW and a mesa structure that is 2.5-μm tall with only the JJ on top, minimizes microwave loss from epitaxial layers, which is critical for superconducting qubits. This presentation will demonstrate gate tunable critical currents and discuss the characterization of MBE-grown Ge JJs along with the path toward integrating these JJs into gatemon qubits.

The superconducting diode effect (SDE), in which supercurrent is asymmetric in applied current bias, can be observed when time reversal and inversion symmetries are broken in a Josephson junction. Recently, changes in the sign of the SDE have been correlated with possible topological phase transitions in certain regimes of linear Josephson junctions. Here we report an even-odd SDE in Corbino-geometry Josephson junctions, where even/odd flux parity states show a SDE alternating in sign. These junctions are fabricated on a single surface of a bulk-insulating three-dimensional topological insulator and can be used for probing signatures of Majorana states that are theoretically present within the junctions under a magnetic field. We fabricate high-quality niobium Josephson junctions on tellurium-capped Sn-doped Bi_1.1Sb_0.9Te₂S (Sn-BSTS) single crystals, with junctions showing high transparency. Additionally, different Corbino-style geometries enable Josephson interferometry within a single junction, allowing us to explore the skewed current-phase relation. Our analysis attributes the flux-parity controlled SDE to a topological phase, with opposite diode polarity directly reflecting the sign change of the periodic boundary conditions for an even/odd number of Josephson vortices in the junction.