Josephson

Josephson is a surname of Scottish origin. It is notably associated with Brian D. Josephson (born 1940), a Welsh theoretical physicist who, in 1962, predicted the Josephson effects in superconductivity and was awarded the Nobel Prize in Physics in 1973 for these predictions.

The Josephson effects describe the flow of superconducting current between two superconductors separated by a thin insulating barrier, known as a Josephson junction, due to tunneling of Cooper pairs. The DC Josephson effect yields a supercurrent with no voltage across the junction, while the AC Josephson effect occurs when a constant voltage is applied, producing an oscillating current at a frequency proportional to the voltage, f = (2e/h) V.

A Josephson junction is formed by two superconductors separated by a thin barrier, which can be insulating or a thin normal metal or a weak link. The barrier controls the critical current and the junction acts as a nonlinear inductive element essential in superconducting circuits. The properties of the junction enable a wide range of low-temperature quantum devices.

Applications include SQUIDs (superconducting quantum interference devices) for ultrasensitive magnetometry, and metrology where the Josephson effect defines precise voltages. In quantum computing, circuits using Josephson junctions form superconducting qubits such as transmons and phase qubits. Additional uses include rapid single flux quantum (RSFQ) logic and microwave amplification.

These concepts have driven advances in low-temperature physics and quantum technologies, with ongoing research to improve coherence, scalability, and integration of Josephson-based devices.