Josephson Effect & SQUIDs
In 1962 Brian Josephson predicts that paired electrons tunnel between two superconductors; the effect gives SQUID magnetometers, the volt standard and the core of superconducting qubits.
Open in the interactive tree →Josephson, then a graduate student at Cambridge, predicted the current and voltage across a thin barrier between two superconductors in 1962; Anderson and Rowell reported its probable observation in 1963, and Josephson shared the 1973 Nobel Prize. The first DC SQUID, built at Ford in 1964, senses magnetic fields down to a few femtotesla per root hertz and is used for brain imaging, geophysics and detector read-out in astronomy. NIST's voltage standard connects 20,208 junctions in series, and a Josephson junction is the nonlinear element of the superconducting qubits in today's quantum computers.
Prerequisites
- Superconductivity1911Paired electrons of the BCS picture tunnel across the barrier
- Quantum Mechanics1925Tunnelling of electron pairs through a thin insulating gap
- Solid-State Physics & Bands1931Thin-film junctions between solid superconductors
Unlocks
- First Quantum Processors2019Superconducting qubits use Josephson junctions as their nonlinear element
- SI Units Redefined (New Kilogram)2019The volt is realised with Josephson junction arrays, whose constant 2e/h becomes exact
- Quantum Tunneling in a Circuit2025The circuits of Clarke, Devoret and Martinis are built around a Josephson junction