Sub-Micrometer Epitaxial Josephson Junctions for Quantum Circuits.

摘要

We present a fabrication scheme and testing results for epitaxial submicrometer Josephson junctions. The junctions are made using a high- temperature (1170 K) 'via process' yielding junctions as small as 0.8 microns in diameter by use of optical lithography. Sapphire (AI2O3) tunnel-barriers are grown on an epitaxial Re/Ti multilayer base-electrode. We have fabricated devices with both Re and AI top electrodes. While room-temperature (295 K) resistance versus area data are favorable for both types of top electrodes, the low-temperature (50 mK) data show that junctions with the Al top electrode have a much higher subgap resistance. The microwave loss properties of the junctions have been measured by use of superconducting Josephson junction qubits. The results show that high subgap resistance correlates to improved qubit performance.