Constriction-Type Superconducting Quantum Device Modified by Local Thermal Effect

Abstract

We report a method to locally modify superconducting materials using nano-laser direct writing, rather than conventional ablation or etching, for the fabrication of constriction-type Josephson junctions and superconducting quantum devices. Specifically, at a fixed laser power of 120 mW, the critical current \(I_c\) can be modified from 250 \(\mu \)A to 80 \(\mu \)A by increasing the pulse width from 3.0 ms to 4.0 ms, establishing an optimal processing window prior to the onset of irreversible film degradation. The optimized SQUID operated at 4.0 K exhibited a voltage-flux modulation depth of approximately 200 \(\mu \)V, a maximum flux-to-voltage transfer coefficient \(V_{\varPhi }\) of 0.75 mV/\(\varPhi _0\), and a white flux noise spectral density of 2 \(\mu \varPhi _0\) Hz\(^{-1/2}\). With its ability to locally modify superconducting properties without material removal, this approach opens new avenues for in-situ tunable Josephson junctions and provides a flexible platform for future superconducting quantum circuits.