An Empirical Method for Predicting the Critical Current of Unshunted Josephson Junctions in a Shielded Room from Measurements in an Unshielded Room

The critical current (Ic) of a Josephson junction (JJ) is a significant physical parameter that plays a crucial role in the design of subsequent devices and circuits, as well as in the optimization of manufacturing processes. To ensure accurate measurements, testing should ideally be conducted in a magnetically shielded room. However, due to laboratory constraints, tests are often performed in unshielded environments, where they are inevitably influenced by various environmental noises. This introduces significant uncertainty into the measured Ic values, thereby impacting the design of subsequent superconducting circuits. This study examines the impact of conductive, radiated, and flux noise on the repeatability of Ic measurements in an unshielded environment and establishes an empirical formula for predicting Ic values in shielded environments based on unshielded data. The deviation between the empirically predicted Ic and the experimentally measured value is less than 1%, verifying the effectiveness of the proposed formula. This approach offers a relatively accurate and cost-effective method for testing the critical current (Ic) of Josephson junctions (JJs) under unshielded conditions.