Predicted in 1962 by 23-year-old Cambridge graduate student Brian Josephson (1973 Nobel Prize) and experimentally confirmed by Philip Anderson and John Rowell at Bell Labs in January 1963.
A zero-voltage DC supercurrent I = I_c sin(φ) flows across the barrier, while a fixed DC voltage V drives an alternating current at frequency K_J·V where K_J = 2e/h ≈ 483.6 THz/V.
Josephson junctions form the core of SQUID magnetometers, the NIST volt standard (an array of 20,208 junctions in series), and superconducting transmon qubits (2025 Nobel Prize to Clarke, Devoret, and Martinis).