I. Introduction
Josephson junctions have been used to develop various ultralow-noise, power-efficient, and high-speed superconducting circuits [1] that are successfully applied in both the analog and digital domains. Superconducting quantum interference devices (SQUIDs) are the first type of practical Josephson junction circuits [2]; they are ultrasensitive flux-to-voltage converters widely used in magnetic field measurements [3], [4]. Single-flux-quantum (SFQ) circuits are ultrahigh-speed and low-power Josephson junction digital circuits [5], [6], promising for the next-generation signal processing and computing systems [7]. Moreover, Josephson junctions have also enabled quantum electromagnetic circuits for quantum computing [8], [9].