Brian David Josephson
active c. 1940, Cardiff, Wales, UK
Welsh theoretical physicist who predicted the Josephson effects — coherent supercurrent tunneling — while still a graduate student at Cambridge.
A Cambridge prodigy who published important work as an undergraduate, Josephson calculated in 1962 the current through a superconducting tunnel junction and found two surprising terms: a DC supercurrent flowing at zero voltage, and an AC current whose frequency locks to the applied voltage at 2eV/h. Experimental confirmation within a year made junctions the basis of SQUID magnetometers and, decades later, superconducting qubits.
Nobel-winning work
Josephson's 1973 Nobel Prize honored 'his theoretical predictions of the properties of a supercurrent through a tunnel barrier, in particular those phenomena which are generally known as the Josephson effects'. Treating both sides of a weak link as a single macroscopic quantum system, he showed that Cooper pairs tunnel coherently: the junction current is I = I_c sin φ, where φ is the phase difference of the order parameters.
The consequences — a dissipationless current at V = 0 and microwave emission at ν = 2eV/h under bias — tied current directly to a voltage-to-frequency conversion fixed by fundamental constants. Josephson junctions became the heart of SQUIDs, the most sensitive magnetometers known, and of today's voltage standard and superconducting quantum computers.
Workplaces: University of Cambridge
United Kingdom