Quantum Interference in DC-SQUIDs Comprising Two Sub-Micron Aluminum Josephson Junctions: Deviation from Classical Model

In a small Josephson junction, the critical current is often found experimentally to be smaller than the value expected fromthe Ambegaokar-Baratoff theory because of the quantum phase fluctuations. We also observed in our previous study that the quantum interference in a dc-SQUID comprising sub-micron Al junctions deviated from the classical model. In this work, we have fabricated 13devices having different values of maximal critical currents, and evaluated their quantum interference patterns.The quantum interference of 12among 13 devices has deviated from the classical model. It is confirmed that their maximal critical currents(Icsq,max) are reduced from the values (Icsq0) predicted by the Ambegaokar-Baratofftheory. Besides, the quantum interference for Icsq,max / Icsq0< 0.4 agrees with themodified quantum-interference model.