Analysis of Multistable Superconducting Quantum Interference Devices (SQUIDs) in Keysight Advanced Design System

Superconducting Quantum Interference Devices (SQUIDs) exhibit exceptional magnetic flux sensitivity due to superconducting phase interference enforced by flux quantization in a closed loop of Josephson junctions (JJs). Under certain bias conditions, JJ nonlinearity induces multistability, creating multiple potential energy minima—critical for designing robust, tunable superconducting qubits. Locating these extrema traditionally requires brute-force searches, which are computationally expensive and poorly integrated into circuit workflows. We introduce the SQUID Extrema Analysis Tool, the first of its kind in a commercial circuit solver (Keysight ADS), implementing the approach of Miano et al. (PRX Quantum 4, 030324, 2023). The tool identifies stable states and extracts associated key physical quantities such as SQUID circulating current, potential energy, and effective inductance, enabling practical design and optimization of multistable superconducting circuits.