DC SQUID ($I_c(\Phi )=2I_0|\cos (\pi \Phi /{\Phi }_0)|$)

A SQUID with two Josephson junctions in a superconducting loop. For equal junctions, negligible self-inductance and no intrinsic phase offset, adding their sinusoidal currents gives the displayed flux-dependent critical current. An rf SQUID instead has one junction and uses loop inductance.

The 1964 report established quantum interference in superconducting tunneling. It is an experimental counterpart to the phase-sensitive current predicted for coupled superconductors.^[ref]