Josephson Effect
The quantum tunneling of Cooper pairs across a thin insulating barrier separating two superconductors (a Josephson junction).
Governing formula
I = I_c sin(Δφ), V = (ℏ / 2e) (dΔφ / dt)
SI unit
mA (Current), μV (Voltage)
In depth
In the DC Josephson effect, a supercurrent flows with zero applied voltage driven by phase difference Δφ across the barrier. In the AC Josephson effect, applying DC voltage V generates high-frequency AC current oscillations at frequency ν = 2 e V / h.
Examples in the real world
Superconducting Quantum Interference Devices (SQUIDs) measuring brain magnetic fields (~10⁻¹⁵ T) and voltage standards.