DC SQUID Interferometer: Flux-Quantized Critical Current

A DC SQUID — two Josephson junctions bridging a superconducting loop — turns quantum phase coherence into the most sensitive magnetic-field detector ever built. Because the Cooper-pair wavefunction must stay single-valued around the ring, the two junctions' phase differences lock to the magnetic flux threading the loop, and the maximum lossless current the loop can carry oscillates with a period of exactly one flux quantum Φ0 = h/2e. This simulator renders the loop and its two junctions in 3D with an animated persistent current, lets you sweep the applied flux (by hand or with an auto-sweep), detune the junctions' symmetry, and push a bias current past the critical current to watch the loop switch from a dissipationless supercurrent into a real resistive voltage state — while a live interference curve plots Ic(Φ) and tracks exactly where you are on it.